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DEC-08-E50UA-A-D

August 1975

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OCR Text

EDUsystem - 50
USERS GUIDE
DEC-08-E50UA-A-D

digital equipment corporation

EDUsystem - 50
USERS GUIDE
DEC-08-E50UA-A-D

August 1975

DIGITAL EQUIPMENT CORPORATION

MAYNARD, MASSACHUSETTS 01754

The information in this document is subject to change without notice
and should not be construed as a commitment by Digital Equipment
Corporation. Digital Equipment Corporation assumes no responsibility
for any errors that may appear in this document.
The software described in this document is furnished under a license
and may only be used or copied in accordance to the terms of such
license.
Digital Equipment Corporation assumes no responsibility for the use
or reliability of its software on equipment that is not supplied by
Digital.

The HOW TO OBTAIN SOFTWARE INFORMATION pages, located at the back of
this document, explain the various services available to Digital software users.
The postage prepaid READER'S COMMENTS form on the last page of this
document requests the user's critical evaluation to assist us in
preparing future documentation.
The following are trademarks of Digital Equipment Corporation:

DIGITAL
DEC
PDP
DECUS
UNIBUS
COMPUTER LABS
COMTEX
DDT
DECCOMM

DECsystem-lO
DECtape
DIBOL
EDUSYSTEM
FLIP CHIP
FOCAL
INDAC

LAB-8

MASSBUS
OMNIBUS
OS/8
PHA
RSTS
RSX
TYPESET-8
TYPESET-ll

LIMITED RIGHTS LEGEND
Contract No.
Contractor or Subcontractor:

Digital Equipment Corporation

All the material contained herein is considered limited rights data
under such contract.

CONTENTS

PREFACE
CHAPTER 1

I~~RODUCTION

1-1

l..l.

USER PROGRAMS

1-2

1.2

USER FILES

1-2

1.3

TSS/8 HARDWARE CONFIGURATION

1-3

EDUSYSTEM 50 MONITOR

2-1

2.1

CALLING THE MONITOR

2-6

2.2

LOGGING INTO EDSYSTEM 50

2-8

2.3

LOGGING OUT OF EDUSYSTEM 50

2-10

2.4

SYSTEM LIBRARY PROGRAM CONTROL

2-13

2.5

TYPING MONITOR COMMANDS

2-13

2.6 '

CONTROLLING OUTPUT

2-13

2.7

COMMUNICATING WITH OTHER USERS

2~14

2.8

HUNG OUTPUT DEVICES

2~15

2.9

SYSTEM STATUS REPORTS

2-15

2.10

RESOURCE SHARING

2-16

2.11

ERROR MESSAGES

2-20

, ,

CHAPTER 2

CHAPTER 3

SYSTEM LIBRARY PROGRAMS

3.1

GENERAL FILE CHARACTERISTICS

3~2

3.2

CONTROLLING THE EXECUTION OF SYSTEM
LIBRARY PROGRAMS

3-5

3.3

RETURNING TO THE MONITOR

3-6

- ii -

CHAPTER 4

CALL ING AND US ING BAS IC

4.1

BASIC

4-1

4.2

LANGUAGE FEATURES

4-2

4.2.1

Trunc"ation Function, FIX (X)

4-2

4.2.2

ON GOTO Statement

4-2

4.2.3

SLEEP statement

4-3

4.2.4

Comments

4-4

4.2.5

Blank Lines

4-4

4.2.6

Multiple Statements per Line

4-5

4.2.7

Editing BASIC Statements

4-5

4.2.8

Saving Comp1i1ed Programs

4-6

4.2.9

File Protection

4-7

4.2.10

Project-programmer Numbers

4-7

4.2.11

Restricted Accounts

4-8

4.2.12

Catalog Format

4-8

4.2.13

Strings in BASIC

4-8

4.2.13.1

Reading string Data

4-9

4.2.13.2

Printing Strings

4-11

4.2.13.3

Inputting Strings

4-11

4.2.13.4

Line Input

4-12

4.2.13.5

Working with Strings

4-13

4.2.13.6

The CHANGE statement

4-14

4.2.13.7

The CHR$ Function

4-16

4.2.14

Program Chaining

4-17

4.3

DISK DATA FILES

4-19

4.3.1

File Records

4-19

4.3.2

Opening a Disk File

4-21

4.3.3

Reading/Writing Disk Files

4-21

4.3.4

Closing/Deleting Disk Files

4-24

4.4

DECTAPE DATA FILES

4-24

4.4.1

DECtape File Records

4-25

4.4.2

Opening a DECtape File

4-26

4.4.3

Reading/Writing DECtape Files

4-27

4.4.4

Closing DECtape Files

4-29

4.4.5

using DECtape Data Files with OS/8
FORTRAN

4-29

4.5

LINE PRINTER OUTPUT

4-29

4.6

INTERNAL DATA CODES

4-30

4.6.1

Numeric Data

4-30

4.6.2

String Data

4-31

4.7

ERROR MESSAGES

4-32

CHAPTER 5

FOCAL

5.1

USING FOCAL COMMANDS

5-1

5-.2

FOCAL OVER VIEW

5-2

5.3

NUMBERS

5-3

5.4

VARIABLE NAMES

5-4

5.5

ARITHMETIC OPERATIONS

5-5

5.5.1

priority of Arithmetic Operations

5-5

5.5.2

Enclosures

5-6

5.6

INPUT/OUTPUT COMMANDS

5-7

5.6.1

TYPE Command

5-7

5.6.2

ASK Command

5-8

5.6.2.1 Text Output with ASK

5-9

5.7

COMMPUTATIONAL COMMAND (SET)

5-9

5.8

CONTROL COMMAND

5-10

5.8.1

GO or GOTO Command

5-10

5.8.2

IF Command

5-11

5.8.2.1

IF with Less Than Three Line
Numbers

5-11

5.8.2.2.

Arithmetic Comparison with IF
Command

5-12

5.8.3

DO Command

5~13

5.8.3.1

Nested DO

5-13

5.8.4

RETURN Command

5-14

5.8.5

QUIT Command

5-14

5.8.6

FOR Command

5-14

5.8.6.1

FOR with a DO

5-15

5.8.6.2

Nested FOR and DO

5-15

5.8.6.3

subscript variables

5-16

5.8.7

COMMENT or CONTINUE Command

5-17

5.9

EDIT COMMAND

5-17

5.9.1

WRITE OR WRITE ALL Command

5-17

5.9.2

ERASE and ERASE ALL Command

5-18

5.9.3

MODIFY Command

5-19

5.10

LIBRARY COMMANDS

5-21

5.10.1

LIBRARY SAVE Command

5-21

5.10.2

LIBRARY CALL Command

5-22

5.10.3

Error Messages with Library Commands

5-22

5.11

ESTIMATING PROGRAM LENGTH

5-23

5-12

DEBUGGING

5-24

- iv -

5.12.1

Using the Error Diagnostics

5-24

5'.12.2

using the Trace Feature

5-25

5.13

FOCAL FUNCTIONS

5-25

5.13.1

Sine Function (FSIN)

5-26

5.13.2

Cosine Function (FCOS)

5-26

5.13.3

Exponential Function (FEXP)

5-27

5.13.4

Logarithm Function (FLOG)

5-27

5.13.5

Arctangent Function (FATN)

5-28

5.13.6

Square Root Function (FSQT)

5-28

5.13.7

Absolute Value Function (FABS)

5-28

5.13.8

sign Part Function (FSGN)

5-29

5.13.9

Integer Part Function (FITR)

5-29

5.13.10

Random Number Function (FRAN)

5-30

5.14

FOCAL OUTPUT OPERATIONS

5.:.;.30

5.15

CONTROL CHARACTERS

5-31

FORTRAN

6-1

6.1

CALLING FORTRAN-D

6-1

6.2

USING FORTRAN-D

6-2

6.3

LINE FORMAT

6-4

6.3.1

Statement Numbers

6-5

6.3.2

statement Continuation Character

6-5

6.4

FORTRAN STATEMENTS

6-6

6.4.1

Comment Statements

6-6

6.4.2

Character set

6-7

6.4.3

Constants

6-7

CHAPTER 6

- v -

5.13

FOCAL FUNCTIONS

5.13.1

Sine Function (FSIN)

5.13.2

Cosine Function (FCOS)

5.13.3

Exponential Function (FEXP)

5.13.4

Logarithm Function (FLOG)

5.13.5

Arctangent Function (FATN)

5.13.6

Square Root Function (FSQT)

5.13.7

Absolute Value Function (FABS)

5.13.8

Sign Part Function (FSGN)

5.13.9

Integer Part Function (FITR)

5.13.10

Random Number Function (FRAN)

5.14

FOCAL OUTPUT OPERATIONS

5.15

CONTROL CHARACTERS

CHAPTER 6

FORTRAN

6.1

CALLING FORTRAN-D

6.2

USING FORTRAN-D

6.3

LINE FORMAT

6.3.1

Statement Numbers

6.3.2

Statement Continuation Character

6.4

FORTRAN STATEMENTS

6.4.1

Comment Statements

6.4.2

Character Set

6.4.3

Constants

6.4.3.1

Integer Constants

6.4.3.2

Real Constants

6.4.3.3

Fixed and Floating-Point
Representation
- vi -

- vii 6.4.3.1

Integer Constants

6-7

6.4.3.2

Real Constants

6-8

6.4.3.3

Fixed and Floating-Point

6-8

Representation
6.4.4

Variables

,.
, n
O-.L.U

6.4.4.1

Integer variables

6.4.4.2

Real Variables

6-11

6.4.4.3

Scalar Variables

6-11

6.4.4.4

Array Variables

6-11

6.4.5

DIMENSION Statement

6-12

6.5

FORTRAN ARITHMETIC

6-13

6.5.1

Arithmetic operators

6-13

6.5.1.1

Use of Parentheses

6-15

6.5.2

Arithmetic Expressions

6-16

6.5.3

Arithmetic Statements

6-17

6.5.3.1

Multiple Replacement

6-18

6.5.4

Functions

6-20

6.6<.

PROGRAM CONTROL STATEMENTS

6-21

6.6.1

END Statement

6-21

6.6.2

STOP Statement

6-21

6.6.3

PAUSE Statement

6-22

6.6.4

GO TO Statement

6-22

6.6.5

Example of Integer Summation

6-23

6.6.6

IF Statement

6-23

6.6.7

00 LOOps

6-25

6.6.7.1
6.6.8

CONTINUE Statement
Computed GO TO

6-28
6-28

6.7
6.7.1

FORTRAN INPUT/OUTPUT

6-29
6-30

Data Formats

6.7.1.1

ASCII Coded Data

6-30

6.7.1.2

Binary Coded Data

6-30

6.7.2

Input/Output Statements

6-30

6.7.2.1

ACCEPT and TYPE Statements

6-31 .

6.7.2.2

Read and write Statements

6-32

6.7.3

Variable Specification in I/O
Statements

6-33

6.7.4

FORMAT Statements

6.7.5

The A Format specification

6-36

6.7.6

Input Format

6-37

6.7.6.1

Integer Values --the I Format

6-37

6.7.6.2

Real Values

6-38

6.7.7

the E Format

output Formats

6-38

6.7.7.1

E and I Formats

6-38

6.7.7.2

FORMATS Control specifications'

6-39

6.7.7.3

Hollerith Output

6-40

6.8

INPLEMENTATION NOTES

6-40

6.8.1

Double Subscripts

6-40

6.8.2

Substatement Feature

6-42

6.8.3

Error Checking

6~43

6.8.4

FORTRAN-D Source program Restrictions

6-44

6.8.5

FORTRAN-D Compiler and operating system 6-44
Core Map

- viii -

- ix 6.9

FORTRAN-D ERROR DIAGNOSTICS

6-45

6 .. 9 .. 1

compiler Compilation Diagnostics

6-45

compiler Systems Diagnostics

6-49

operating system Diagnostics

6-50

PAL-D ASSEMBLER

7-1

7.1

INTRODUCTION

7-1

7.2

EDUSYSTEM 50 PAL-D

7-2

7.3

SYNTAX

7-2

6.9.3
CHAPTER 7

7.3.1

Legal Characters

7-3

7.3.2

Illegal Characters

7-4

7.3.3

Format Effectors

7-4

7.4

NUMBERS

7-6

7.4.1

Arithmetic and Logical Operators

7-6

7.4.2

Evaluating Expressions

7-7

7.5

STATEMENTS

7-7

7.5.1

Labels

7-8

7.5.2

operators

7-8

7.5.3

Operands

7-8

7.5.4

Comments

7-9

7.6
7.6.1

SYMBOLS

7-9

Symbol Distinction

7-9

7.6.1.1

permanent Symbols

7-9

7.6.1.2

User-Defined Symbols

7-10

7.6.2

Symbolic Address

7-11

7.6.3

Symbolic Operators

7-12

7.6.4

Symbolic operands

7-12

7.6.5

Symbol Table

7-12

7.6.6

Direct Assignment Statements

7-13

7.7

ADDRESS ASSIGNMENTS

7-14

7.7.1

Current Address Indicator

7-17

7.7.2

Indirect Address

7-18

7.7.3

Auto indexing

7-20

7.7.4

Literals

7-21

INSTRUCTIONS

7-23

7.8
7.8.1

Memory Reference Instructions

7-23

7.8.1.1

Paging

7-24

7.8.1.2

Off-Page Referencing

7-25

7.8.2

Augmented Instructions

7-25

7.8.2.1

Operate Microinstructions

7-25

7.8.2.2

Input-Output Transfer
Microinstructions

7-27

7-9

PSEUDO-OPE-RATORS

7-31

7.9.1

Current Location Counter

7-31

7.9.2

Extended Memory

7-31

7.9.3

RADIX Control

7-32

7.9.4

Listing Control

7-32

7.9.5

TEXT Facility

7-32

7.9.6

End of Program

7-33

7.9.7

End of Fi~e

7-33

7.9.8

Altering the Symbol Table

7-34

7.9.9

Internal Representation

7-34

- x -

7.10

PROGRAM PREPARATION AND ASSEMBLER
OUTPUT

7-35

7 .. 10.1

Program File

7-35

n ?
....1 "".,...

Assernbly

7-37

7.10.3

Pass 1

7-37

7.10.4

Pass 2

7-38

7.10.5

Pass 3

7-38

7.11

OPERATING THE PALD ASSEMBLER

7-39

7.12

ERROR DIAGNOSTICS

7-42

UTILITY PROGRAMS

8-1

8.1

SYMBOLIC EDITOR

8-1

8.2

LOADER

8-2

8.3

OCTAL DEBUGGING TECHNIQUE (ODTHI)

8-6

8.4

CATALOG (CAT)

8-7

8.5

SYSTEM STATUS (SYSTAT)

8-9

PROGRAMS FOR HANDLING DATA

9-1

PERIPHERAL UTILITY TRANSFER ROUTINES
(PUTR)

9-1

CHAPTER 8

CHAPTER 9
9.1

9.1.1

PUTR Commands

9-1

9.1.1.1

ZERO Commands

9-10

9.1.1.2

DELETE Commands

9-11

9.1.1.3

DIRECTORY Commands

9-11

9.1.1.4

LIST Command

9-12

9.1.1.5

TYPE command

9-12

9.1.1.6

PUNCH Command

9~13

9.1.1.7

TAPE Command

9-13

- xi -

9.1.1.8

EXIT Command

9-13

9.1.1.9

special Notes

9-13

9.1.1.10

Default Propagation

9-15

9.1.1.11

DECtape and RK~5 Disks

9-16

9.1.2

TSS/8 File Extensions

9-17

9.1.3

PUTR Switches

9-17

9.2

PERIPHERAL INTERCHANGE PROGRAM (PIP)

9-18

9.2.1

PIP Conventions

9-18

9.2.2

Paper Tape to Disk Transfers

9-19

9.2.3

Disk to Paper Tape Transfers

9-19

9.2.4

High-Speed Reader/Punch Assignments 9-20

9.2.5

BIN Format File Transfers

9-21

9.2.6

Moving Disk Files

9-21

9.2.7

Deleting Disk Files

9-21

9.3

COPY PROGRAM

9-22

9.3.1

using and calling COPY

9-22

9.3.2

Loading Files from DECtape

9-23

9.3.3

saving Disk Files on DECtape

9-23

9.3.4

Listing Directories

9-24

9.3.5

Deleting Files

9-25

9.3.5.1

Deleting All Existing Files on a
Device

9-25

9.3.6

Example of COPY usage

9-26

9.3.7

BASIC File Transfers

9-28

9.3.8

Save Format File Transfers

9-28

- xii -

CHAPTER 10

ADVANCED MONITOR COMMANDS

10-1

10.1

INTRODUCTION

10-1

10.2

CONTROL OF USER PROGRAMS

10-3

10.3

DEFINING DISK FILES

10-4

10 .. 3 .. 1

Creating a Disk File

10-5

10.3.2

opening and Closing a File

10-5

10.3-.3

Extending, Reducing, and Renaming
a Disk File

10-6

10.3.4

Protection Codes

10-7

10.3.5

Error Conditions

10-10

10.4

SAVING AND RESTORING USER PROGRAMS

10-10

10.5

UTILITY COMMANDS

10-14

WRITING ASSEMBLY LANGUAGE PROGRAMS

11-1

11.1

INTRODUCTION

11-1

11.2

CONSOLE I/O

11-2

11.3

FILES AND DISK I/O

11-6

11.4

ASSIGNABLE DEVICES

11-14

11.5

PROGRAM CONTROL

11-21

11.6

PROGRAM AND SYSTEM STATUS

11-23

11.7

PDP-8 COMPATIBILITY

11-28

CHAPTER 11

- xiii -

APPENDIX A
A.l

MONITOR COMMAND SUMMARY

A-I

MONITOR COMMANDS

A-I

A.l.l

Logging In and Out

A-I

A.l.2

Device Allocation

A-2

A.I.3

File Handling

A-2

A.l.4

Control of user Programs

A-3

A.l.S

utility Commands

A-4

APPENDIX B

CHARACTER CODES

B-1

APPENDIX C

STORAGE ALLOCATION

C-l

C.l

STORAGE MAP

c-l

C.2

FILE DIRECTORIES

C-l

ERROR MESSAGES

D-l

APPENDIX D*
D.I

BASIC ERROR MESSAGES

D.2

CAT ERROR MESSAGES

D.3

COPY ERROR MESSAGES

D.4

DECODE ERROR MESSAGES

D.S

FOCAL ERROR MESSAGES

D.6

FORTRAN-D COMPILER COMPIIJATION DIGNOSTICS

D.7

FORTRAN-D COMPILER SYSTEMS DIAGNOSTICS

D.S

FORTRAN-D OPERATING SYSTEM DIAGNOSTICS

D.9

LOADER ERROR MESSAGES

*NOTE: Information on the above can be found from page D-l through D-27.

- xiv -

NOTE:

D.IO

LOGID ERROR MESSAGES

D.II

MONITOR ERROR MESSAGES

D.12

NON-FATAL

D.13

PAL-D ERROR DIAGNOSTICS

D.14

PERIPHERAL INTERCHANGE PROGRAM (PIP)
ERROR MESSAGES

D.15

PERIPHERAL UTILITY TRANSFER ROUTINES
(PUTR) ERROR MESSAGES

EXECu~ION

ERROR MESSAGES

Information on the above can be found from page D-l through D-27.

- xv -

CHAPTER 1

INTRODUCTION

EduSystem SO is a general purpose, time-sharing system for PDP-8
computers· that offers up to 20 users a comprehensive library of System
Programs. These programs provide facilities for editing, assembling,
compiling, debugging, loading, saving, calling, and executing user
programs on-line. An extended BASIC language provides users with the
ability to use strings, files, and program chaining. Two higher-level
languages, FOCAL and FORTRAN, are also provided. All languages and
utilities may be used simultaneously. One group of users may be
working in BASIC while another is using assembly language. EduSystem
SO serves all levels of users simultaneously.
By separating the central processing operations from timeconsuming interactions with human users, the computer can, in effect,
work on a number of programs simultaneously. Cycling between programs
and giving only a fraction of a second at a time to each program or
task, the computer can deal with many users seemingly at once. The
appearance is created that each user has the computer to himself. The
execution of various programs is done without their interfering with
each other and without lengthy delays in the response to individual
users.
The heart of EduSystem SO is a complex of subprograms called the
Monitor. The Monitor coordinates the operations of the various programs and user consoles, ensuring that the user is always in contact
with his program. The EduSystem 50 Monitor allocates the time and
services of the computer to the various users; it grants a slice of
processing time to each job, and schedules jobs in sequential order
to make most efficient use of the system disk. The Monitor handles
user requests for hardware operations (reader, punch, etc), swaps
(moves) programs between memory and disk, and manages the user's
private files.
1-1

1.1

USER PROGRAMS
When the user is working with EduSystem 50, it appears to him as

though he had his own 4K (4096 word) PDP-8 computer.

He then has the

capability of doing anything which can be done in a 4K computer plus
the capabilities of the Monitor.

Several users can run different

programs at virtually the same time because the Monitor controls the
scheduling of execution times.

The Monitor brings a program into

core from the disk, allows it to execute for a short time, and takes
note of the state at which execution is stopped.

The user is allotted

a 4K block of core that contains his particular program; this 4K block
is swapped (moved) from core onto a 4K area of disk when the Monitor
needs to bring another user program into core to be executed.
After the user's program has been executed for a period of time,
it is placed at the end of the queue (line) of user programs waiting
to be run.

If only one program is ready to run, it is allowed to do

so without interruption until another program is ready.

If a user

wishes to maintain a permanent copy of his program, he can save a
copy within the file area of the disk (an area separate from the
swapping area) or on DECtape or paper tape.
1.2

USER FILES
A user is any person logged into EduSystem 50.

Each user has an

account number and password assigned to him by the System Manager.
The account number and password allow the user to gain access to the
computer.

The account number is also used to identify whatever files

the user may own within the EduSystem 50 file system.
The system disk is divided into logical areas called files.
user can store programs or data in files on the system disk.

The user

can further specify which users may access his files and for what
purpose (read, write, or both).

Parts of the disk are used to store

system files, those programs which are accessible to anyone using

1-2

the system.

A major portion of this manual deals with how to use

the system files, generally called System Library Programs.
With the appropriate Monitor commands, the user can create new
files and manipulate old files (extend, reduce, or delete them).
These commands are summarized in Table

~l.

Most individual System

Library Programs are able to handle user files as input or output
with commands issued from the user's console.

Such commands are

described under the section on the appropriate System Library Program.
1.3

TSS/8 HARDWARE CONFIGURATIONS
A minimum configuration for TSS/8 includes:
a)

PDP-8, 8I, or 8E, with at least 12K words of memory and the
time-share option.
(All are referred to in the following
text as PDP-8.)
For efficient operation, 16K minimum is
highly recommended.

RF08 disk with at least one RS08 (can use DF32 with at least
two platters, but this is not recommended because of very
little area and slow speed).

Multi-terminal capability - one or more KL8Es or PT08s or
a DC08A.

All, except 81 with DC08A, require a real-time clock.
Optional hardware supported:
a)

Up to 32K words of memory.

DC08A - may be used only on a PDP-81 and may be used in
addition to PT08s.

689AG modem controller - for use with DC08A only.

EAE - all instructions of any standard EAE are supported
with the exception of the traditional PDP-8 step counter:
which is not saved or restored.

High-Speed Reader - a paper tape reader is required to
build TSS/8. A low-speed reader may be used, however the
build procedure will be very time consuming.

High-Speed Punch.
1-3

Line Printer - LP08/LE8 or LSOS/LS8E.

DEC tape - TCOl or TC08 and up to eight drives (NOT TDSE).

Up to four disks (three additional RSOSs).

Card Reader.

RK-SE disk (up to four drives).

Power failure protection.

MISEF or MISEG hardware bootstrap.

Software provided with the Standard EduSystem 50 includes the
following:
•

General-purpose time-sharing Monitor System.

•

Time-shared BASIC language processor.

•

Time-shared assembly language package including text editor,
symbolic assembler, loader, and utility debugging program.

•

Time-shared FORTRAN-D and FOCAL language processors.

•

System-utility programs, including PUTR, PIP COPY, etc.

•

Library of sample programs, textbooks, and curriculum
guides.

1-4

CHAPTER 2
EDUSYSTEM 50 l'-lONITOR

EduSystem 50 Monitor controls the allocation and use of hardware
resources". Many of these functions of the Monitor are invisible, and
of no concern to the user, for example; the way it allows many users
to run programs on a single computer. In other instances, the user
explicitly tells the Monitor what he would like to do by typing one
or more of the Monitor commands described in this chapter.
The Monitor commands described in the first half of this chapter
are those needed to log into the system, to utilize the System
Library Programs, and to log out of the system. All users must be
familiar with these commands. The commands described in the last
half of this chapter are not needed to run System Library Programs
such as BASIC or FOCAL but are frequently useful. The Advanced
Monitor commands described in Chapter 10 are primarily useful for
creating assembly language programs and files. Table 2-1 contains a
summary of the Monitor commands.
TABLE 2-1.
Monitor Commands

Explanation

Logging In and Out
LOGIN Cl Sl

LOGOUT

Request to login:
Cl = user's account number
51 = user's password
Request to logout: processing and
console time are printed.

2-1

Table 2-1. (Cont.)
Monitor Commands
TIME C1

Explanation
Request printout of processing time:
C1 = job number
If C1 is omitted and the user is
logged i~ the processing time of the
current job is printed. If C1 = ~,
or if the user is not logged in and
C1 is omitted the time of day is
printed.

Device Allocation
ASSIGN L1

Reserve device:
L1 = R for paper tape reader
P for paper tape punch
L for line printer
C for card reader
D for any DECtape unit
K for any RK~5 unit

ASSIGN Ll C1

Reserve specific unit
L1 = D for DECtape
K for RK~5
C1 = unit number

RELEASE Ll

Release device:
L1 = R, P, L, or C (see ASSIGN L1)

RELEASE L1 C1

L1 = D for DECtape
K for RK~5
C1 = unit number

File Handling
CLOSE S1

Close files:
81 = list of internal file numbers

CREATE Sl

Create new file:
S1 = name of new file

EXTEND Cl D1

Extend length of file:
Cl = internal file number
Dl = number of segments to be
added to end of file

F Cl

Print information about an open file.
Cl = internal file number
2-2

Table 2-1.
Monitor Conunands
OPEN C1 S1 C2

(Cont.)
Explanation

Establish association between internal
file number and file:
Cl = internal file number
Sl = file name
C2 = account n~~her.
If C2 is omitted, the user's account
is assumed.

PROTECT C1 C2

Protect a file:
Cl = internal file number
C2 = new file protection mask
(see 10.3.4)

REDUCE C1 Dl

Reduce length of file:
Cl = internal file number
D1 = number of segments to be
removed from end of file

RENAME Cl Sl

Rename a file:
C1 = internal file number
S1 = new name of file

Control of User programs
DEPOSIT Cl C2 ••• Cn

Store in core memory:
C1 = location
C2 = contents to be stored in
Location C1
C3 = contents to be stored in
Location C1+1, etc.

EXAMINE Cl Dl

List specified contents:
Cl = first location
Dl = number of location to be listed
D1<10 decimal

RESTART

Print the program restart address.

RESTART Cl

Set program restart address.

START

Restart user program.

2-3

Table 2-1.
Monitor Commands
START C1

(Cont.)
Explanation

Execute user program:
Cl = starting location

utility Commands
BREAK

Print current keyboard break mask

BREAK C1

Set keyboard break mask:
Cl = new mask

DUPLEX

Echo typed characters on printer.

LOAD Cl Sl
LOAD C1 Sl C2
LOAD Cl Sl C2 C3
LOAD C1 Sl C2 C3 C4
LOAD Sl
LOAD Sl C2
LOAD Sl C2 C3
LOAD S1 C2 C3 C4

Load core image:
Cl = owner's account number; if
not specified the user's
account is assumed.
Sl = name of file
C2 = file address of first word to
be loaded; if not specified,
¢ is assumed.
C3 = core address of first word to
be loaded; if not specified,
¢ is assumed.
C4 = core address of last word to
be loaded; if not specified,
the highest possible value is
assumed.

R Sl

Run system file:
Sl = name of file
Cl = starting address; if omitted,
¢ is assumed

R S1 C1

RUN Sl
RTJN Cl Sl
RUN Sl C2
RUN Cl Sl C2

RUN USER FILE:

STOP execution

Sl = name of file
Cl = owner's account number; if
omitted the user's account is
assumed.
C2 = starting address; if omitted,
¢ is assumed.

2-4

Table 2-1.

(Cont.)
Explanation

Monitor Commands
SAVE Cl Sl

SAVE core image:
Cl = owner's account number; if not
specified, the user's account
is assumed.

SAVE C1 Sl C2

SAVE C1 S1 C2 C3

SAVE Cl S1 C2 C3 C4
Sl = name of file

SAVE Sl
SAVE Sl C2
SAVE Sl C2 C3
SAVE Sl C2 C3 C4

C2 = file address of first word to
be saved; if not specified, ¢
is assumed.
C3 = core address of first word to
be saved; if not specified, %
is assumed.
C4 = core address of last word to
be saved; if not specified, the
highest possible value is
assumed.

SWITCH

Print the value of the user's switch
register.

SWITCH Cl

Set switch register:
Cl = word to be set

TALK Cl Sl

Send a message to console Cl:
Cl = destination console
Sl = message

UNDUPLEX

Inhibit echo of characters typed to a
user program.

USER

Print the user's job number, account
number, and console number.

USER Cl

Print the job number, account number and console number of job CIa

WHERE

Print the current value of the user's
switch register, PC, Link, AC, and EAE
registers.

2-5

NOTE
All Monitor commands must be terminated
by typing the RETURN key. All words
within a Monitor command line are separated by one or more spaces.

2.1

CALLING THE MONITOR
The user enters commands to system programs, such as BASIC and

FOCAL, in exactly the same way that he enters commands to the Monitor
(i.e., by typing them at the keyboard); therefore, the system must
have some way of distinguishing between the two cases.
defining two modes of console operation:
mode.

It does so by

Monitor mode and program

When a user's console is in Monitor mode, all input is inter-

preted as being commands to the Monitor.

Otherwise, all input is

assumed to be to the user program or system program· which is being
run by the user.

2-6

A special character, CTRL/B (obtained by pressing B with the
CTRL key held down, and echoed on the terminal as tB), is used to
unconditionally place the user's console in the Monitor mode.
Typing CTRL/B tells the system that the command to follow is a
Monitor command, regardless of the current console mode. Generally,
the command which follows the CTRL/B will be the S command.

tB
tBt BS

Return to Monitor mode.
Return to Monitor mode from a program which is
printing.
(The two CTRL/B's stop the printout,
allowing the S command to be typed.)

It is not necessary to precede each Monitor command with CTRL/B.
Once in the Monitor mode, a console stays in that mode until a command is entered to start a system program. To signify that the
console is in the Monitor mode, the system prints a dot (.) at the
left margin of the console printer paper. This dot indicates that
the characters entered next are to be treated as a Monitor command.
Thus, the CTRL/B capability is important when a user is running a
program and wishes to issue a Monitor command. He may, for example,
be using one language (or system program) and want to change to
another, as shown below:
NOTE
Characters typed by the user are underlined
to eliminate confusion with characters
printed by the system .
• R FOCAL
SHALL I RETAIN LOG, EXP. ATN ?:NO
SHALL I RETAIN SINE. COSINE ?:NO
PROCEED.
*TYPE 6+10-3-1
•
12.0100*TYPE 25+5*2+5
•
41.1"'.'85

2-7

.R BASIC
NEW OR OLD--NEW
.ZV PROGRAM NAME-Notice that the Monitor responds to CTRL/B followed by S, by printing
a dot at the left-hand margin.
2.2

LOGGING INTO EDUSYSTEM 50
To prevent unauthorized usage and to allow the Monitor to main-

tain a record of system usage, EduSystem 50 requires that each user
identify himself to the system before using it.

Before attempting to

log into the system, the user should ensure that the console LINE/OFF/
LOCAL knob is set to LINE and then press the RETURN key.

If the con-

sole is connected to EduSystem 50 and is not already in use, the
Monitor rolls the console paper up two lines and prints a dot at the
left margin of the paper.

The dot indicates that the system is in

Monitor mode and that the Monitor is waiting for a command.

The

LOGIN command allows the user to gain access to EduSystem 50.
The user types LOGIN followed by an account number and password.
Providing the console is free (not already logged in), the command,
account number, and password are not printed on the console paper as
the keys are typed.

If the command name letters are being printed,

stop typing the command; instead, strike the RETURN key, log out
using the LOGOUT command (see Logging out of EduSystem 50).
point, a successful LOGIN can be accomplished.

At this

The LOGIN command is

formatted as shown below:

.LOGIN 1234 ABCD

(only the dot appears)

The dot (.) is printed by the Monitor, LOGIN is the command name,
1234 represents the user account number, and ABCD represents the
password.

2-8

NOTE
A command word and each parameter
(except the last) is always followed
by a _spac~.· _Command lines are always
terminated with the RETURN key. The
RETURN key enters the full command
line to the system.
When. a user types something other than a val .;d
. . LOGIN
. ..... ~omm
~
. and ,
the Monitor responds in one of the following ways:

•

ILLEGAL REQUEST

(user typed LOGIN ABCD ABCD)

.LOGIN 4771 DEMO
ALREADY LOGGED IN

(user typed valid LOGIN on an already
logged in console)

•

(user typed ASSIGN D 3)

•

(user typed an incorrect account
number or password)

UNAUTHORIZED ACCOUNT

In the third example, ASSIGN D 3 is a valid command but is not
appropriate until the user is logged into the system.

In the first

example, the Monitor finds that the LOGIN command is improperly formatted (the first parameter must be a 1- to 4- digit number): the
console print out tells the user that he has made an ILLEGAL REQUEST.
When the console is already logged in and the user types the LOGIN
command, the characters typed echo at the console and the Monitor
informs the user that the console is occupied with the message
ALREADY LOGGED IN.
If the user attempts to use an incorrect account number or password, the Monitor replies UNAUTHORIZED ACCOUNT. Thus the Monitor can
distinguish an invalid command from a valid command: it can also distinguish whether the valid command is appropriate when issued,

2-9

whether the command is properly formatted, and whether the account
number and password are acceptable.

In all the preceding examples,

Monitor ignores the command and prints another dot.
When the Monitor finds the LOGIN command properly formatted and
the account number and password acceptable, it responds by identifying the version of the system being used, the job number assigned to
the user, the number of the console being used, and the time-of-day

in hours, minutes, and seconds.

This information is usually followed

by a note from the System Manager concerning the system.

•

T55/8.24

JOB 01

[00,03]

K04

For example:

15126113

YOU ARE NOW LOGGED INTO THE BHS EDU5VSTEM 50
PROCEED AT YOUR OWN SPEED

The Monitor then prints another dot and waits for the user to
issue the next command.

The job number assigned is an internal num-

ber by which the system identifies each on-line user; the user need
not remember this number.
2.3

LOGGING OUT OF EDUSYSTEM 50
The LOGOUT command indicates to the Monitor that the user is

finished and ready to leave his terminal.

When Monitor receives a

LOGOUT command, it disconnects the user terminal from the system and
records the amount of computer time used during the session and the
total real time of the session.
or saved.

It also notes any user files deleted

For example:

.LOGOUT
JOB 1, USER [12,34] LOGGED OFF K00
AT 19:20:19 ON 27 NOV 74
DELETED 1 FILES ( 1. DISK BLOCKS>
SAVED 11 FILES ( 38. DISK BLOCKS)
RUNTIME 00100&24 ( 7. CPU UNITS)
ELAPSED TIME 02:14&39

2-10

computer processing time used in this example was 24 seconds, while
the elapsed time between LOGIN and LOGOUT was 2 hours, 14 minutes,
and 39 seconds.
When

ty~ing

the LOGOUT command, the user may follow it with a

colon and an option to initiate some action by the system.
To specify
an option, the user types, for example:
.LOGOUT:K
If no option is specified, the S option is assumed: similarly if a
user is simultaneously logged in at two (or more) consoles, no files
will be deleted until he logs off his last
• LOGOUTI?

job~

For example:

TYPE tBS TO ABORT LOG-OUT; OR
TYPE ONE OF THE FOLLOWING (AND CAR RET):
K
L
S
I

TO KILL JOB AND DELETE ALL UNPROTECTED FILES;
TO LIST YOUR DISK DIRECTORY;
TO SAVE ALL (NON-TEMPORARY) FILES; OR
TO INDIVIDUALLY SAVE AND DELETE FILES AS FOLLOWS:
AFTER EACH FILE NAME IS LISTED. TYPE:
P TO SAVE AND PROTECT.
S TO SAVE WITHOUT PROTECTING. OR
CAR RET ONLY TO DELETE.

CONFIRM: L
.BIN
FIE
BAS000.TMP
BAS100.TMP
INTER .BAS
.FCL
PROC

<17>
<17>
<17>
<17>
<12>

1 • BLOCKS
1 • BLOCKS
1 • BLOCKS
1 • BLOCKS
2. BLOCKS

CONFIRM: I
.BIN
FIE
BAS000.TMP
BAS100.TMP
INTER • BAS
.FCL
PROC

<17>
<17>
<17>
<17>
<12>

1 • BLOCKS
1 • BLOCKS
1 • BLOCKS
1 • BLOCKS
2. BLOCKS

: S
: DELETED
I DELETED
:
: S

JOB I. USER [ 3.13] LOGGED OFF K00 AT 10:46:07 ON 27 NOV 74
DELETED
3 FILES (
3. DISK BLOCKS)
SAVED 2 FILES (
3. DISK BLOCKS)
RUNTIME 00100125 ( 2. CPU UNITS)
ELAPSED TIME 00106:12

2-11

JOB 1, USER (3,13) LOGGED OFF K¢¢ AT l¢: 46:¢7 ON 11-27-74
DELETED
3 FILES (
3. DISK BLOCKS)
SAVED 2 FILES (
3. DISK BLOCKS)
RUNTIME ¢¢:¢¢:25 ( 2. CPU UNITS)
ELAPSED TIME ¢¢:¢6:12
In the previous example, the user typed a question mark to check
the LOGOUT options.

When LOGOUT completed the printed explanation,

it printed CONFIRM: and waited for a user reply.

In this case, the

user requested a listing of his files, LOGOUT followed this listing
with a second CONFIRM: to which the user replied I.

When using the I

option, the user is advised not to type his reply to individual entries
until printing stops.

DELETED is printed automatically by the system

to show that the temporary files are deleted without user intervention.
The user saved binary file FIE and the FOCAL file PROG.

The BASIC

file INTER was deleted by typing the RETURN key.
An optional method of logging out of the system is to type K in
response to the Monitor dot or K followed by a colon and an option
designation.

For example:

JOB 1. USER [12.34] LOGGED OFF K00 AT 19120:19 ON 27 NOV 74
SAVED 3 FILES (
4. DISK BLOCKS>
RUNTIME 08100107 ( 1. CPU UNITS>
ELAPSED TIME 11113:57
A complete list of the logout option can be found in table 2-2
on pag~ 2-13.6
~.

. . ..

2-12

2.4

SYSTEM LIBRARY PROGRAM CONTROL

Once logged into the system, the user can call any EduSystem 50
system Library program.

To call a library program, the user types

the command R (meaning run) followed by one or more spaces and the
program name.

For example:

.R BASIC
NEW OR OLD-2.5

TYPING MONITOR

COMMANDS

When typing a command to the Monitor,

it is possible to correct a

letter without retyping the entire line.
(or DELETE) key.

To do this, press the RUBOUT

This will remove characters from the end of the line

one by one, and print the deleted characters.

When the incorrect

characters have been removed, continue typing the correct line.
To erase an entire command line and start over, type CTRL/B and
then the desired command.

2.6

CONTROLLING OUTPUT

An optional feature of the Monitor allows the user to suspend
terminal output from the Monitor.

If, for example, he is running a

program which causes much output, he may type a CTRL/S (t S).
signals the Monitor to stop sending to the terminal.
wishes to see more output, he types a CTRL/Q (tQ)
from where it left off.
sned the

~ Sand

This

When the user

, and output continues

Users with a'VT50 can cause the terminal to

fQ automatically.

2-13

2.6.1 System Library Program Control
Once logged into the system, the user can call any EDUsystem
50 System Library Program. To call a library program, the user

types the command R (meaning run)

followed by one or more spaces

and the program name. For example:
.R BASIC
NEW OR OLD

TABLE 2-2
LOGOUT OPTIONS
Function

Option
:I

Allow the user to individually decide which files to
save or delete. Temporary files are deleted
automatically.

Delete all unprotected files from piske

List the user's file directory. After listing the
files, the system prints CONFIRM: and the user replies
with one of the options.

LOGOUT without any printed message.

Save all nontemporary files.
one of the following:

A temporary file is

BASOnn
BASlnn
TEMPnn
where nn is the console number at which the user is
logged into the system. A temporary file is created
by a System Library Program and listed in CATALOG
listings. A temporary file is also considered to
be any file with a .TMP extension.
If no option is
specified in the LOGOUT command, :S is the default.

Print a listing of the available options and their
functions.

The Monitor fetches the BASIC language processor from the
System Library and starts it.

BASIC begins its dialog by asking if

2-13.5

the user wishes to work on a new program or retrieve an old one
from disk storage.

Notice that once BASIC begins, the console is

no longer in Monitor mode.

Dots are no longer printed at the margin.

All input is now processed'by the BASIC language processor.
If the user types a program name which cannot be found in the
System Library, the Monitor responds with an error message and
returns the console to the Monitor mode, as follows:

2-13.6

.R BASICK

FILE NOT FOUND
The exact contents of a System Library may vary from installation to installation.

The System Manager may choose to make any

number of programs available to all users.
2.7 COMMUNICATION WITH OTHER USERS
Although EduSystem 50 gives each system user the impression that
he is the only user of the system, it is actually supporting many
users at a time.

Often it is useful to communicate with another

user, or with the system operator: this is done with the TALK command.

The TALK command requests the Monitor to print a message on

another system terminal.

For example, a user at terminal 7 can ask

the system operator to turn on the high-speed punch by typing the
following command (the initial dot is printed by the Monitor) :
.TA 0 PLEASE TURN ON THE HIGH·SPEED PUNCH.
The above command causes the following to be printed at console O •
•• K07

[12~34J

••

PLEASE TURN ON THE HIGH·SPEED PUNCH.
K07 indicates that terminal 7 sent the message.
can initiate a message to any other terminal.

Any terminal

However, if the

destination terminal is printing at that time, the message will not
be sent.

The initiating terminal would, in this case, receive the

message BUSY as a response.

2-14

2.8

HUNG OUTPUT DEVICES
When the paper tape punch or line printer is off line or
hung, the Monitor takes special action so that it is usually
possible to continue with little or no data loss.

When these

devices are hung, the output buffer is not cleared.

A system

error is generated, and regenerated every few seconds until the
condition is cleared.

If the user program has not enabled

errors, the result will be a printed "HUNG DEVICE" message,
and then the terminal bell will ring, trying to persuade the
user to do something.

There are only two things the user may

do to remove himself from this condition.

If he is not interes-

ted in continuing, he may release the hung device.

If he does

wish to continue he should put the device on line, and it should
take off.
2.9

He may now type ItSTART" to continue program execution.

SYSTEM STATUS REPORTS
The command SYSTAT initiates a printout of the full status
of EduSystem 50, how many users are on-line, what they are
doing, etc.
SYSTAT.

The command SYSTAT is equivalent to typing R

The format of the status report is described in the

section on Utility Programs.
The user can obtain information on the amount of computer
time used by him, the amount used by another user, or obtain
the time of day with the TIME command.

The TIME command can be

issued in one of the following three forms:

2-15

TIME

Returns the elapsed processor time of the user
issuing the TIME command since he logged into
the system. If the user is not logged in, the
time of day is returned.
--

TIME 0

Returns the time of day_

TIME n

Returns the amount or processor time used by
job n since logging into the system.

For example:

.TIME
00:00:00

.TIME "
15:31'18
.TIME 10
"0:00'34

2.10

RESOURCE SHARING
All system users, when logged into the system, have access
to the System Library, disk storage, a virtual 4K PDP-B, and
the EduSystem 50 Monitor.

The Monitor handles disk resource

requests automatically.

The Monitor also maintains a pool of

available devices which are assigned to users upon request on
a first-come, first-served basis.

Devices such as the high-

speed paper-tape reader cannot, by their very nature, be assigned
to several programs simultaneously.

Therefore, the Monitor

grants individual users exclusive access to these devices when
needed.

The system disk is not assigned since it can be used

by more than one user simultaneously.

2.-16.

All systems include a high-speed paper-tape reader in the pool
of available devices.

Many systems also include a high-speed paper-

tape punch, a high-speed line printer, a card reader, RK8E, and/or
one or more DECtapes.

These assignable devices are normally used

with the System Library Program PUTR to store programs or data for
later use.
When a device is assignable (present on the system) and available
(not being used), the ASSIGN command may be used to reserve the
desired unit or units for exclusive use by the console issuing the
command.

The valid ASSIGN commands are formatted as shown below:

ASSIGN C

Assign the card reader.

ASSIGN D

Assign a DEC tape unit.

ASSIGN K

Assign a RKf,3'S unit.

ASSIGN L

Assign the line printer.

ASSIGN P

Assign the high-speed paper-tape punch.

ASSIGN R

Assign the high-speed paper-tape reader.

If other devices are assignable, the System Manager will inform
the user of the appropriate device designator.

The following is an

example of using an invalid device designator:
.ASSIGN X

ILLEGAL REQUEST

The Monitor ignores the request, responds with the appropriate
message, and prints another dot.

When a valid ASSIGN command is

issued, the Monitor checks the availability of the device and
responds accordingly.

For example:

-ASSIGN R
R ASSIGNED

-ASSIGN P

JOB 0e

[12.34]

KnS
l?

HAS . P

•
2-17

When the system contains multiple units of a device, the user
simply specifies the device; the Monitor assigns an available unit
and responds with the ~~it n~~ber. For example:
.ASSIGN D
D 0 ASSIGNED

If all DECtape units are busy, the Monitor prints the message
shown below:
.ASSIGN D
DEVICE NOT AVAILABLE

A specific unit can be requested by leaving a space between the
device designator and the device number.

For example:

.ASSIGN D 4
D 4 ASSIGNED

The ASSIGN command assigns only one device at a time. Therefore,
when multiple devices are to be assigned, each must be assigned
separately. The following will not accomplish the desired assignments,
either with or without the illegal commas .
• ASSIGN R ~ D a~ D 1
R ASSIGNED

The Monitor accepted the first device designator and ignored the
rest of the command. If device R is unavailable, the Monitor prints
the appropriate message. The following commands complete the desired
assignments (assuming available devices):
.ASSIGN D 2
D 2 ASSIGNED

.ASSIGN D 1
D 1 ASSIGNED

2-18

When the user has finished working with an assigned device, he
should use the RELEASE command to terminate the assignment and allow
other users access to the device.
(When a user logs out of the
system, any devices still assigned to him are automatically released.)
A particular device is released when the user enters the RELEASE
command, a space, and the device designator (and unit number if
required), as shown below:
.RELEASE R
.RELEASE D 3

In the previous example, the high-speed reader and DEC tape unit
3 are released. The Monitor prints a dot on the next line if the
release is accomplished; otherwise, it prints a message. If, for
example, a request is made to release a device which has not been
assigned to the issuing console, the following happens:

.RELEASE D 2
ILLEGAL REQUEST

The Monitor printed ILLEGAL REQUEST after it checked and found that
the specified device was not assigned to the console issuing the
command.
NOTE
All commands must be formatted properly;
ILLEGAL REQUEST is printed if the user
fails to separate the device designator
and unit number with a space.
When multiple device units were reserved by a user, each must
be individually released. For example:
.RELEASE D 1
.RELEASE D 2
.RELEASE R

•

_2-19

The Monitor does not perform checking when releasing a device
as it does when assigning a device.

The user may have two device

units (e.g., two DECtape units) assigned and Monitor would not know
which to release; therefore, device numbers. are necessary with a

RELEASE cOITmand.

~~en

only one unit of a specific device (one high-

speed reader or punch, etc.) is on the system, the device designator
alone is sufficient.
2.11 ERROR MESSAGES
An appropriate error message is printed whenever:

a Monitor

command cannot be performed at the time it is requested, a typing
error is made, or the command is illegal (or nonexistent).

Following

each error message, the Monitor ignores the command and prints
another dot, after which the user can issue another command.

Table

2-3 is a list of the Monitor error messages.
TABLE 2-3
MONITOR ERROR MESSAGES
Message

Explanation

ALREADY LOGGED IN

The user tried to log in on a console
which is already in use.

BUSY

The user attempted to talk to a console
which is currently printing or on which
another user is typing.

DEVICE NOT AVAILABLE

An ASSIGN command has been entered for
either:

FULL

a device which is not present on
the system, or

a device which is temporarily busy
and should be available in a few
seconds.

The system is full.
Another user cannot
log in until one of the present users
logs out.

2-20

Table 2-3.
Message

(Cont.)
Explanation

ILLEGAL REQUEST

The user requested an illegal command. This error usually results
when some parameter has been given
an incorrect value or the request
refers to a facility not owned by
the user.

The user attempted to use a console
which is not logged into the system.

Sl??

The System Interpreter does not
understand the command. Sl=command.

TYPE tBS FIRST

The user attempted to use a system
command which cannot presently be
honored due to the status of the
user's program.

UNAUTHORIZED ACCOUNT

The user 'attempted to log into the
system with an invalid account
number or password.

WAIT FOR I/O

A request cannot be honored because
a device is busy. Try typing the
command again.

2-21

CHAPTER 3
SYSTEM LIBRARY PROG~~
The System Library contains a comprehensive set of user programs
for a wide range of applications.

Language processors; such as BASIC

and FOCAL, allow the user to code and run programs in interactive
languages.

FORT'

FORTRAN language.

compiles and executes programs written in
A complete assembly language system allows programs

to be written in PALO, assembled, and run.
perform special functions.

Various utility programs

The DEC-supplied System Library consists

of the following programs.

•

BASIC - an easily learned interactive language originally
developed at Dartmouth College.

•

CAT - used to list all the files which a user has stored in
his library.

•

COpy - a utility program used to transfer files between the
system disk and DECtape.

•

EDIT - a line-oriented text editor, used to create and
modify source programs (such as FORTRAN) and data files.

•

FOCAL - DEC·s own interactive language for on-line problem
solving, designed especially for use on mini-computers.

•

FORT

•

LOADER - a binary loader used to load assembled programs
for execution.

•

ODTHI - Octal Debugging Technique for testing and modifying
assembly language programs.

•

PALD - a 2-pass symbolic assembler.

•

PIP - Peripheral Interchange Program for transferring files
between the system disk, paper tape, and line printer.

•

Pu~R - a utility program used to transfer files between all
EduSystem 50 devices.

•

SYSTAT - (System Status) a utility program that prints a
brief description of the system status.

- a modified version of FORTRAN II.

3-1

A more detailed description of each of the above System Library
Programs is presented in the following sections.
3.1

GENERAL FILE CHARACTERISTICS

A fundamental feature of the Monitor is its ability to save
programs or other data for each user in his own private library.
These individual user libraries are maintained on the system disk.
Individual entries in the library are called files, whether they
contain programs or data. Within the library itself, there is no
distinction between types of files by their contents. Each file is
identified with a file name by which it is known and called into use.
The user does not directly create and update the files in his
library. He uses the System Library Programs for this purpose. For
example, he can use the SAVE command in BASIC. The SAVE command
takes the BASIC program named and saves it as a file in the user's
library for future use. Similarly, EDIT can be used to modify an
existing file, resulting in the creation of a new file. Therefore,
although the Monitor provides the actual file storage capability,
most file manipulation is done while System Library Programs are
being run.
The System Library Programs which operate on these files must
know which file to use, when to create a new file, and what to call
it. Each Library Program has its own method of determining whether a
user wishes to use an old file or create a new one; this is explained
in the sections on individual library programs.
Example 1:
.R BASIC

NEW OR OLD--OLD
OLD PROGRAM NAME--PRIME
R~~

3-2

Example 2:
.ft

FORT

INPUTtTYPE
OUTPUT.BTYPE
For most of his work, the user requires access to only his own
library. However, it is often a useful feature to be able to obtain
a program from another user's library, allowing a single file to be
shared by several users. To access a program from another user's
library, the user must tell the system in which individual library
the file is stored. The user tells the system by entering the account
number of the library's owner.
(In the absence of an account number,
the user's own library is the assumed source.) To get a file from the
System Library, type an asterisk immediately after the file name.
Example 1:

.R BASIC
NEW OR OLD--OLD
OLD PROGRAM NAME--HOSSR*
READY
.ft PALD

INPUTINOTPIP 5440
OUTPUT. BINI
NOTE
Most examples in the discussions of individual System Library Programs use file
names within the user's own library. The
user is free (file protect permitting) to
use files from other user's libraries.
Access to another user's files is gained only with his permission.
A user may "protect" his files against other users, i.e., prevent them
from gaining access to his files, even though they know his program

3-3

name and account number.

Library Programs never permit a user to

write in another user's files.

Specifying a file which is protected,

or specifying a nonexistent file, is an error that is detected
immediately.

An error message is printed and the file name is

requested again.
The user places his output in a single file; however, it is
often useful to input several files together.

(For example, the user

may wish to assemble two parts of a PAL-D program together.)

specify more than one input file, separate the file names by commas.
No Library Program (except PUTR) allows more than three input files.
FORTRAN is limited to two; BASIC allows only one.
BASIC is a self-contained programming system, with an editor,
compiler, and run-time system.

It also has a distinctive file format.

Files created by BASIC are not compatible with files created by other
Library Programs.

All other Library Programs depend on each other;

therefore, all other Library Programs use the same format for their
disk files.

Consequently, files created by the Editor can be used

as input to PAL-D or FORTRAN programs as data files.
The Monitor includes a disk quota system, which limits the
amount of file space that each account can have.

A user can find

out what his own quota is by running the program CAT.

Any time an

account exceeds this disk quota, the Monitor will print a message such
as [MYFILE EXCEEDING DISK QUOTA] warning the user that he is about to
run out of disk space.

The amount by which he may exceed his disk

quota is called the grace quota, and is defined by the System Manager.

3-4

Up to this point, only files that exist within the time-sharing
system, i.e., on the system disk, have been described; however,
EduSystam 50 provides other means of file storage such as paper tape,
RK~5

cartridge disk/and DECtape.

The Library Progr~us PIP, COPY,

and PUTR can be used to transfer data between any devices which are
present on the System.
3.2

CONTROLLING THE EXECUTION OF SYSTEM LIBRARY PROGRAMS
EduSystem 50 provides the user with two options for stopping the

system.

CTRL/C (C with the CTRL key held down) allows the user to

stop his BASIC program and return to the beginning of that program
without returning to the Monitor.

For example, if the user begins

to run a BASIC program that has an endless loop, he can type CTRL/C
to stop it.

BASIC responds to tc with READY.

All other Library

Programs respond in a similar manner.
CTRL/B is used to stop the Library Program most recently called.
CTRL/B followed by S and the RETURN key unconditionally returns the
user to the Monitor mode; the user can then call another Library
Program.

If the system is printing, two CTRL/B's and the S (tBtBS)

are required to stop the system.
RUBOUT is another useful character that deletes the last typed
character.

Some Library Programs respond by printing \

others print the deleted character.

or -

while

If the RUBOUT key is typed while

entering file names for input or output to a Library Program, RUBOUT
deletes the whole line.

The request for input or output is then

repeated.

3-5

3.3

RETURNING TO THE MONITOR

The user can stop the execution of a System Library Program at
any time by typing CTRL/B followed by S and the RETURN key. The
System Library Programs can also initiate a return to the Monitor.
When the System Library Programs initiate a return, tBS is printed
just as though the user had terminated the program. For example,
BASIC returns to the Monitor when the user types the BYE command:
READY

BYE
tSS

•
FORTRAN returns to the Monitor after completing execution of a
program. CAT and SYSTAT return after printing their particular data
output. PAL-D returns after completion of an assembly, LOADER at
the end of a normal load, and EDIT after completion of an EDIT.
FOCAL, ODT, and PIP never return to the Monitor; these programs must
be terminated by the user with CTRL/B followed by S. Some System
Library Programs return to the Monitor when a fatal error condition
is detected.

3-6

CHAPTER 4
CALLING AND USING BAS.IC

4.1

BASIC

EduSystem 50 BASIC is a time-sharing version of the BASIC
language. It allows even the beginning computer user to write and
run meaningful programs. In addition, EduSystem 50 BASIC has advanced language features such as strings, files, and program chaining.
This section describes the BASIC language capabilities riot discussed in
Chapter 1 of the EduSystem Handbook. Table 4-4 contains a complete
summary of the EduSystem 50 BASIC language.
To call BASIC, the user types:
.R BASIC
After the user logs into EduSystem 50; and calls BASIC in the above
manner, BASIC prints NEW OR OLD--. The user then types the appropriate adjective: NEW (if he wants to enter a new program) or OLD (if
he wants to retrieve a program that was previously filed).
BASIC then asks NEW PROGRAM NAME-- (or OLD PROGRAM NAME--) and
the user types any combination of six letters or less. If the user
is recalling an old program file from the disk, he must use exactly
the same name as when he originally instructed BASIC to save it.
BASIC prints READY to signal the start of the editing phase;
the user then begins to type the new program. If the user types a
line consisting of only a line number followed by the RETURN key,
that line is deleted. Each line must begin with a line number
greater than 0 and less than 2047 and which contains no non-digit

4-1

characters.

To enter an entire line to the computer, the user must

press the RETURN key.
If the user makes a typing error while typing a statement and
notices it immediately, he can correct it by typing the RUBOUT (or
DELETE) key (right-hand side of the keyboard), or the back arrow key.
Typing either key deletes the character in the preceding space and
prints a backarrow

(~)

character for each character erased.

user can then type the correct characters.

The

Typing the RUBOUT key a

number of times erases one character from the current line (spaces
are characters) to the left for each RUBOUT typed.
While BASIC is in the editing phase, certain additional commands
(which must not have line numbers) are available.

The commands are

described in Table 4-4 under Edit/Control Commands.
4.2

LANGUAGE FEATURES

4.2.1

Truncation Function, FIX (X)
The truncation function returns the integer part of X.

For

example:
10 PRINT "FIX(10.2)." FIXC10.2)
20 END

RUN
FIX(ll.2)· I I

FIX is like INT for positive arguments, and can be defined as:
FIX(X)
4.2.2

= SGN(X) * INT(ABS(X»

ON GOTO Statement
The ON ..• GOTO statement may be used to provide a many-way branch.

The general form of the ON •.• GOTO is:

4-2

ON expression GOTO line number, line number ...
If the value of the integer part of the expression is 1, a GOTO is
performed to the first statement.

If the value of the integer part

of the expression is 2, a GOTO to the second statement number is
performed, etca

If the value is less than one, or greater than the

number of statement numbers, the program terminates and an error
message is printed.

999 ON N GOTO

Examples of ON GOTO are shown below:

100~400~200~600~499

872 ON A+SQRCS*C) GOTO
4.2.3

108~200

SLEEP Statement
The SLEEP statement causes a BASIC program to pause for a

specified interval, then continue running.

SLEEP is followed by the

number of seconds the program is to pause.

For example:

222 SLEEP 38
or
228 LET N-1S

222 SLEEP 2*N

causes a 30 second delay in the program.
The SLEEP statement is a useful way for a program to wait for a
device (DECtape or line printer) which is busy.

The ELSE clause in

the OPEN statement can go to a routine which pauses for a while, then
retries the OPEN.

When the current user finishes with the device and

releases it, the program may then proceed to OPEN and use it.

This

capability is especially useful when many users may be looking up
information on a single DECtape file.

It may also be used to allow

two programs to communicate with each other.

Each writes information

on a tape file for the other, or others, to read.

4-3

SLEEP should always be used when waiting for a device. While
the program is sleeping it is not using any processor time. A SLEEP
time of 30 to 60 seconds is recommended. It is particularly important
that the program not wait by repetitively retrying the OPEN. To do
so wastes computer time and slows down other users. The integer part
of the argument is used to determine the number of seconds to delay.
This value must be between 0 and 4095.
4.2.4

Comments
An entire statement of comments may be included in the BASIC

program by means of the REM statement. Often comments are easier to
read if they are placed on the same line with an executable statement
rather than in a separate REMARK statement. This can be accomplished
by ending an executable statement with an apostrophe. Everything to
the right of the apostrophe up to the statement terminator (carriage
return or backslash) is ignored (unless the apostrophe occurs within
a print literal or string constant.) For example:
10 LET X=Y 'THIS IS A COMMENT'
28 PRINT "SUT THIS IS NOT A COMMENT"
38 LET XS·flA'S"

Thus, a comment is added to line 10 with an apostrophe, but in lines
20 and 30 the apostrophe is treated as a valid character.
4.2.5

Blank Lines

To make BASIC programs easier to read, blank lines can be inserted anywhere in a BASIC program. These can be used to break a
program into logical sections, or (as is often done) to insert
remarks with the apostrophe feature. For example:
1"'PROGRAM WRITTEN BY SAM JONEX-S
18"

4-4

Note that to insert a blank line, you must type one or more spaces
after the line number; typing the line number alone will just delete
that line from the program.
4.2.6

Multiple Statements Per Line
As many statements as will fit may be typed on a single program

line.

Each statement must be separated by the backslash character

"~'e

The only statement requiring a line nQmber is the initial one.
For example:

10 FOR 1=1 TO 10\PRINT I\NEXT I
Note that the backs lash character acts as a statement terminator and
thus cannot be included in a comment statement.
4.2.7

Editing BASIC Statements
If a program line is incorrect, it can be corrected by retyping

it.

Minor errors in statements can be corrected by using the EDIT

command.

The user types EDIT followed by the line number of the

statement to be edited.
([).

BASIC responds by printing a left bracket

The user then types a search character.

BASIC prints a close

bracket and prints the statement through the first occurrence of the
specified search character.

The user may then:

Type new characters which are inserted at that point in the
statement.

Type one or more back arrows (-) to delete characters to
the left of the search character.

Type the ALT MODE key to delete the entire line up to that
point (but not the line number)e

Type CTRL/L to continue to the next occurrence of the
search character.

Type CTRL/G to specify a new search character.

4-5

6.
7.

4.2.8

Type LINE FEED to finish the edit, keeping the remainder
of the line unchanged.
Type RETURN to finish the edit, deleting the remainder of
the line.
Saving Compiled Programs

BASIC compiles the current program each time it is run. If,
however, a program will be used frequently without being changed, it
may be stored in its compiled form. A compiled program can be retrieved and executed faster than a BASIC source program. To save a
compiled program, the user types, for example:
COMPILE FAME
The program is saved on the disk under the specified name (FAM& in this cas4
If a file by that name exists, BASIC prints DUPLICATE FILE NAME and
does not compile that program.
Once a program has been compiled, it may be retrieved and run
just like an ordinary BASIC source program. It may not, however, be
listed, saved, or changed. If an attempt is made to do any of these
things, the message EXECUTE ONLY is printed. The compile capability
may therefore be used to protect programs from unauthorized listing
or changing. Since only BASIC source programs can be edited, the
user may wish to store both a source and a compiled version of a
given program.
Compiled files are distinguished from regular BASIC programs by
their file extensions. BASIC source programs have an extension of
.BAS. Compiled files have an extension of .BAC. These extensions
are printed along with the file name when a catalog is requested.

4-6

4.2.9

File Protection
EduSystem 50 permits a user to specify a protection code for

each file.
(See Chapter 10 for a full description of protection
codes.) The commands which write disk files (SAVE, REPLACE,
COMPILE) also permit the user to specify what protection is to be
given to a file. This is done by following the file name with the
protection code in angle brackets. For example:
SAVE DEMO <10>
will create and save a file named DEMO.BAS having a protection code
of 10. When no protection is specified, a protection of 12 is automatically assumed.
4.2.10

Project-Programmer Numbers

In specifying the Account Number prior to requesting an OLD file,
the user may optionally type a Project-Programmer number (giving the
Account Number as two 2-digit numbers separated by commas instead of
a single 4-digit number). In this way, the user may RUN files from
another user's disk area. For example, both of the following are
acceptable:
OLD PROGRAM NAME--FILE 13.3
where 13 is the Project Number and 3 is the Programmer Number, or:
OLD PROGRAM NAME--FILE 1303
where 1303 is the account numbere

The two file name indications are

equivalent.

4-7

4.2.11

Restricted Accounts

As an added system protection, BASIC checks to see if an
attempt is being made to run BASIC under Accounts 1 or 2. If so,
BASIC prints the error message:
IMPROPER ACCOUNT ,
ABORT
IBS
thus preventing BASIC from interfering with the System Directories
or the System Library.
4.2.12

Catalog Format

The CATALOG command prints the user's directory, file names
and file extensions, file size, and file protection codes. For
example:
CATALOG
NAME
SIZE PROT
TEMP00
1 12
DEMO • BAS
1 10
IBOLD .SAC
1
10
BAS000.TMP
1 17
BAS100.TMP
1
17
4.2.13

Strings in BASIC

EduSystem 50 BASIC has the ability to manipulate alphabetic
information (or strings). A string is a sequence of characters,
each of which is a printing ASCII character (see Appendix B) .
EduSystem 50 strings consist of one to six characters; strings of
more than six characters are truncated on input to six characters.

4-8

Variables can be introduced for simple strings, string arrays,
and string matrices. A string variable is denoted by following the
variable name with the dollar sign character ($). For example:
Al$
V$(7)
M$(l,l)

A simple string of up to six characters.
The seventh string in the array V$(n).
An element of a string matrix M$(n,m).

When string arrays or matrices are used, a DIM statement is
required. For example:

reserves space for eleven 6-character strings for the array V$, and
space for 36 6-character strings for the matrix M$.
4.2.13.1 Reading String Data -- Strings of characters may be read
into string variables from DATA statements. Each string data element
is a string of one to six characters enclosed in quotation marks.
The quotation marks are not part of the actual string. For example:
10 READ AS .. BS .. CS
200 DATA ·-JONES" .. "SMI TH .... "HOWE"
The string JONES is read into A$, SMITH into B$, and HOWE into C$.
If the string contains more than six characters, the excess characters
are ignored.

The following program:

10 READ AS
20 PRINT AS
30 DATA "TIME-SHARING"
40 END
RUN
causes only
TIME-S

4-9

to be printed.
String and numeric elements may be intermixed in DATA statements.
A READ operation always fetches the next element of the appropriate
type. In the following example:

10 READ A.lAS.lB
20 DATA '"tES".I2.S.I"NO".I1

2.5 is read into A, YES into A$, and 1 into B.
The standard RESTORE statement (as described in Chapter 4) resets
the data pointers f~r both string and numeric elements. Two special
forms of the RESTORE command, RESTORE· and RESTORE$, may be used to
reset just the numeric or string data list pointers, respectively.
For example:

10 READ A.lAS.lB
20 DATA "YES".I2.5.1"NO",,1

30 PRINT A.lAS"B
40 RESTORE*
50 READ A"AS"B
60 PRINT A"AS"B

70 END

RUN

would print:
YES
NO

1
1

If line 40 were changed to RESTORE, this program would print:

YES
YES

1
1

since the numeric as well as string data lists would be reset.

4-10

4.2.13.2 Printing Strings -- The BASIC PRINT statement may be used
to print string information. If the semicolon character is used to
separate string variables in a PRINT command, the strings are printed
with no intervening spaces. For example, the program:
10 READ AS .. aS"Cs
20 PRINT CSJBSJAS
30 DATA "ING""ttSHAR",,"TIME- 1t

lI0·END
RUN

causes the following to be printed:

TIME-SHARING
4.2.13.3

Inputting Strings -- String information may be entered into

a BASIC program by means of the INPUT command.

Strings typed at the

keyboard may contain any of the standard ASCII characters on the user
terminal except back arrow (-) and quotation mark ("). Back arrow is
used in BASIC to delete the last character typed. Commas are used as
terminators just as with numeric input. If a string contains a comma,
the entire string must be enclosed in quotation marks.
program demonstrates string input.

The following

10 INPUT AS"BS"CS
20 PRINT CS"BS"AS

30 END
RUN

? JONES"SMITH"HOWE
HOWE
SMITH

JONES

READY

Strings and numeric information may be combined in the same
INPUT statement as in the following example. Note that if an input
string contains more than six characters, only the first six are
retained.

4-11

10 INPUT A"AS"BS
20 PRINT AS"BS"A
30 END
RUN
? 01754"MAYNARD"MASS.
MAYNAR
MASS.

1754

The numeric variable A is set to 1754 (leading zeros are deleted),
the string MAYNAR is put in the string variable A$, and the string
MASS. is put into the string variable B$.

To print the number 01754,

the number could be input and output as a character string.
4.2.13.4

Line Input -- Strings of more than six characters may be

entered by means of the LINPUT (line input) statement.

A LINPUT

statement is followed by one or more string variables.

For example:

The first six characters to by typed are stored in the first string
variable, the next six in the second, and so until the line of input
is terminated by a carriage return.
Commas and quotes are treated as ordinary characters and hence
are stored in the string variables.

For example, if the following

line were typed in response to the above LINPUT command:
?MAYNARD" MASS. 01754
then the values of the string variables would be as follows:
A$ (1) = IlMAYNAR"
A$ (2) = liD, MAS
A$ (3) = liS. 017"
A$ (4) = 115411
A$ (5) = 11111
IStrings may consist of zero characters. Such a string is empty (or
null). If printed, it causes nothing to be output. The null string
is usually represented by a pair of quotes with nothing between ("11).
The null string should not be confused with a string of one or more
spaces.
II

4-12

In the above example, the maximum number of characters which
could be typed would be 30.
ignored.

Any additional characters would be

In all cases, the maximum number of characters which may

be typed in response to LINPUT is 50.
message LINE TOO LONG is printed.

If a longer line is typed, the

The input line is ignored and

must be reentered.
It is possible to mix numeric and string variables in a LINPUT
statement, but this practice is not

recorr~ended.

As an illustration

of how this might be done, consider the example given earlier:
18 LINPUT

A~AS~BS

where the user might type:

11754~MAYNARD~

This still sets the numeric variable A to 1754 (when used in LINPUT
statements, numeric input remains unchanged).

However, the string

variable A$ would now be MAYNAR, and the. string variable B$ would
be D, MA.
When inputting strings with LINPUT, the error messages:

MORE?

and TOO MUCH INPUT, EXCESS IGNORED cannot occur.
4.2.13.5

Working With Strings -- Strings may be used in both LET

and IF statements.

For example:

10 LET YS-"YES"
20 IF ZS-"NO" THEN lIe
The first statement stores the string YES in the string variable Y$.
The second branches to statement 100 if Z$ contains the string NO.
For two strings to be equal, they must contain the same characters
in the same order and be the same length.

4-13

In particular, trailing

blanks are significant since they change the length of the string.
"YES" is not equal to "YES "
The relational operators < and> may also be used with string
variables. When used with strings, these operators mean "earlier
in alphabetic order" or "later in alphabetic order", respectively.
They may. be used to alphabetize a list of strings, for example. The
relation operators >=, < =, and < > may be used in a similar manner.
The arithmetic operations (+, -, *, I,t) are not defined for strings.
Thus statements such as LET A$ = 3*5 and LET C$ = A$+B$ have no
meaning, and should not be used in a BASIC program. They will not
cause a diagnostic to be printed; however, the results of such
operations are undefined.
4.2.13.6 The CHANGE Statement -- The CHANGE statement may be used to
access and alter individual characters within a string. Every string
character has a numeric ASCII code (see Appendix B), a number which
is used to indicate that particular character. The CHANGE statement
converts a string into an array of numbers, or vice versa. The
CHANGE statement has the form:
18e CHANGE A TO AS

or
181 CHANGE AS TO A

where A$ is any string variable (or an element of a subscripted
string variable) and A is an array variable with at least six elements.
Any array variables used in CHANGE statements must have appeared in a
DIM statement with a dimension of at least six.
The following program illustrates the use of the CHANGE statement by changing a string variable into an array of numbers.

4-14

II DIll A(6)
20 READ AS

30 CHANGE AS TO A
40 PRINT A(0)lAC1)lA(2)JA(3)JAC4)JA(5)JA(6)
50 DATA "ABeD"
60 END

RUN
4

The CHANGE statement takes each character of the string and stores
its corresponding numeric (ASCII) code in elements one to six of the
array. Remaining array elements are set to zero. The length of the
string (0-6 characters) is stored in the zero element of the array.
In the example above, the character codes for A, B, C, and Dare
stored in A(l) to A(4). A(S) and A(6) are set to zero. The number

4 is stored in A(O) since the string A$ is four characters long.
CHANGE may also be used to change an array of numeric codes into
a character string as in the following ·program:
10 DIM A(6)

20 FOR I-e TO 5
30 READ ACI>
40 NEXT I
50 CHANGE A TO AS
60 PRINT AS
70 DATA 5~69~68~85~53~48
80 END

RUN
EDU50
The length of the resulting string is determined by the zero element of the array. In the previous example, the string is five
characters long. The elements of the array, starting at subscript 1,
are assumed to be numeric character codes; these are converted to
characters and are stored in the string. If any codes encountered
are not valid character codes, or if an invalid string length is
given, the message BAD VALUE IN CHANGE STATEMENT AT LINE n is printed,
and execution is stopped.

4-15

A BASIC string of less than six characters always has the remaining character positions filled with zeros. For this reason, when
such a string is changed to an array, the first six array elements
are set to zero. The CHANGE statement always fills six array elements, even though the strings may not be six characters long. The
user should be careful to dimension the array used in a CHANGE statement to at least six. If a string of characters is transformed into
an array of less than six elements, an undetected error will occur.
The CHANGE statement is usable with strings not created by
BASIC. It may, for example, be used to access files other than
BASIC data files. Each string variable corresponds to three PDP-8
words. The CHANGE statement treats these three words as six 6-bit
bytes, converts each 6-bit byte to its numeric character code
equivalent and stores it in the corresponding array element. The
zero element of the array, the string length, is set equal to the
number of bytes (characters) before the first zero byte. When reading unspecified data, there may be non-zero bytes following this zero
byte. If so, they will be transferred to the array as well.
4.2.13.7 The CHR$ Function -- Occasionally, it is desirable to type
a character other than those in the printing ASCII set, or to compute
the value of a character to be printed. For this purpose, the CHR$
function can be used in a PRINT statement. The argument of the CHR$
function is sent as an ASCII character to the Teletype. For example:
10 FOR 1=0 TO 9
20 PRINT CHRS(I+48)J
30 NEXT I
40 END

prints 0123456789, since 48 to 57 are the ASCII values for the
characters 0 to 9. The following special characters can also be
printed using the CHR$ function:

4-16

Bell
Line feed
Carriage return
Quote (")
Back arrow (-)
Form feed

CHR$(7)
CHR$ (10)
CHR$(13)
CHR$(95)
CHR$(12)

The Teletype will accept characters from 0 to 255 (decimal),
many of which do nothing on most kinds of teletypes. Some of the
special (non-printing) characters should not be used. For example,
CHR$(4) causes a Dataphone to disconnect.
For each ASCII code there is a second acceptable form permitted
in CHANGE and CHR$. The second code is obtained by adding 128 to
the code given in the table in Appendix Ba For example, CHR$ would
type A in response to either 65 or 193 as an argument.
4.2.14

Program Chaining

Most programs are easily accommodated by EduSystem 50 BASIC. If
a program becomes very long, however, it may be necessary to break it
into several segments. Typically, programs of more than two to three
hundred statements must be split into more than one file. A program
that has been broken into more than one piece is commonly called a
chained program.
Each part of a chained program is saved on the disk as a separate
file. The last statement of each part to be executed is a CHAIN
statement specifying the name of the next part of the program. The
next file is then loaded and executed. It may in turn chain to still
another part of the program. The general form of the chain co~uand is:
1&14 CHAIN "NAME"

or
414 CHAIN AS

4-17

where NAME is the name of the next segment to be executed (one to
six characters enclosed in quotation marks). The name of the next
segment may also be contained in a string variable. In either case,
the file of that name is loaded and run. Thus, the statement:
999 CHAIN "SEG2··

is equivalent to:

OLD
OLD PROGRAM NAME-·SEG2
READY

RUN
except that it happens automatically. Each separate part of the
program automatically links to the next part of the program chain.
The individual sections of a chained program may be either
regular source files (.BAS) or compiled files (.BAC). If the sections
are source files, they must be compiled before they are run. A
chained program runs more efficiently if all its sections have been
compiled. Source and compiled files cannot be mixed in program files.
If an error occurs while compiling or running a chained program,
the name of the section containing the error is printed as part of the
error message. In all cases, whether a program terminates by an error
or a STOP or END, BASIC returns to the first program in the chain.
This is the one which is available for editing and rerunning when
BASIC prints READY.
Most chained programs require that information from one section
be passed to the next. The first section may, for example, accept
input values and perform some preliminary calculations. The intermediate results must then be passed to the next section of the programs. This passing of values is done by means of data files which
are explained in the next section. Whenever a CHAIN operation is
performed, program data which has not been saved in a file is lost.

4-18

Variable and array values are not automatically passed to the next
program.'

4e3

DISK DATA FILES
The standard BASIC language provides two ways of handling pro-

gram data items.

They may be stored within the program (in DATA

statements) or they may be typed from the terminal.
however, allow for only a limited amount of data.

DATA statements,
Also, the data is

accessible only to the program in which it is embedded.

Typing data

from the terminal allows it to be entered into any program, but this
is a time-consuming process.

In either case, the data or results of

calculations cannot be conveniently stored for future use.

All these

limitations may be overcome by the use of disk data files.
A data file is separate from the program or programs which use
it.

It is a file on the disk similar to a saved program, but it

contains numbers or strings rather than program statements.
information may be read or written by a BASIC program.

This

(Information

in a data file is stored in a coded format; therefore, it cannot be
listed by the BASIC Editor or EDIT.)

(The maximum size of a data file

is about 350,000 characters.)

String and numeric information may be

combined in a single data file.

The number of data files a user may

have is limited to about 100, space allowing.

When a file is first

created, its contents are undefined.
4.3.1

File Records
A data file is made up of logical units called records.

record may be as small as a single numeric or string variable.
typically, it is a group of variables or arrays.

The design of the

program usually dictates the most efficient size of the record.

If,

for example, the program manipulates a series of 5 by 5 matrices,
each record could contain one such matrix.

If the 'program operates

on SO-character alphanumeric records, 14 string variables might
comprise a record.
4-19

The size and composition of a record are defined with a RECORD
statement. Like the DIM statement, RECORD is followed by a series of
variables. They may, however, be unsubscripted as well as subscripted.
For example:

10 RECORD A(5~S)
10 RECORD 81(14)

10 RECORD A~B~CS(8)~D~E(5)
The set of variables mentioned in a RECORD statement, taken
together, constitute a record. Each element within the record is a
field. Numeric and string information may be mixed to comprise a
more convenient record.
Variables mentioned in a RECORD statement should not appear in
a DIM statement. The RECORD statement reserves variable space
exactly as a DIM statement does. The difference is that the variables
are also identified as being used for file input and output. Nonsubscripted variables appearing in RECORD statements must not have
been used previously in a p~ogram; therefore RECORD statements should
always be the first statements in a program.
Records may be any length. A long record is typically more
efficient since more information is transferred in a single operation.
Records should, however, be only as long as necessary since excess
variables lengthen the file. In particular, it is important to
remember that all arrays and matrices have zero elements. The array
A(5,5) has 36 elements, not 25. If A appears as part of a record,
all 36 elements should be used.
It is also useful to try to make record sizes 43 variables long,
or a multiple of 43. Each RECORD statement reserves program variable
space in units of 43 whether or not the record is that big. Unless
the record fills this area, some program variable space is wasted.
It is not worthwhile, however, to make an inherently small record 43
variables long just to conform to this convention; this would make
the file unnecessarily large.
4-20

4.13.2

Opening a Disk File

Disk data files are completely separate from the programs which
use them.

Therefore, the program must specify which file or files

it will use.

The OPEN command is used for this purpose.

OPENing a

disk data file associates it with an internal file number, either 8 or
9.

(A program may have two disk data files open at one time.)

For

example:

II. OPEN 9 .. "DATAII"
OPEN 8 .. AS
I

The name of the file to be opened may be explicitly stated in
the OPEN command.

If it is, it must be contained in quotation marks.

The file name may also be contained in a string variable, allowing
the program to decide which file to open, perhaps on the basis of
input from the program's user.

In either case, the name of the file

is preceded by the internal file number, either 8 or 9.

This argu-

ment may also be an expression whose value is either 8 or 9.
When a file is opened on an internal file nwuber which has a
file already open, the previously opened file is closed and the new
file opened.
If no file of that name exists, the file is created.

In either

case, once the file is open, it is available for both reading and
writing.

BASIC disk data files are assigned an extension of .DAT

which need not be specified as part of the file name in the OPEN
statement.
4.13.3

Reading/Writing Disk Files

Once open, files may be read and written, one record at a time,
using the GET and PUT statements.

GET statements read one record

of information directly into the variable in the RECORD statement.

4-21

PUT statements write the present values of the variables in the
RECORD ·statement. Both GET and PUT statements are followed by the
internal file number (8 or 9 or an expression), the line number of
the RECORD statement containing the variables to be transferred, and
the name of a control variable. For example:

II' RECORD A.B.CS(30).DCS)
110 OPEN S."FILE1"

120 LET 1-0
131 GET 8.111.1

The control variable specifies the file record to be transferred.
In the example above, FILEl is opened as in~ernal file 8. The value
of the control variable, I, is zero. The GET statement in line 130
reads the first record (record 0) of FILEl into A, B, and the arrays
C$ and D. Single numeric values are read into A and B. 31 strings
are read in C$, and 9 numeric values are read into D. After each
transfer, whether it is a GET or a PUT, the value of the control
variable is automatically incremented. Successive GET's or PUT's
automatically proceed to the next record of the file.
The PUT statement has a similar format.
130 of the preceding program had been:

For example, if line

131 PUT 8.180.1

the present values of A, B, C$ and D would have been written to the
first record of FILE1.
File records may be accessed randomly by setting the control
variable to the desired record number before doing the GET or PUT.
Single records may be read, changed, and then written without processing the entire file. When reading a file, the record referenced
in the GET statement must, of course, be the same as the record
referenced in the PUT statement which wrote the data onto the file.
The total length of the record and the relationship of string and

4-22

numeric fields within the records used for the GET's and PUT's must
be the same. If they are not, improper information will be read and
written.
New files may be created by opening a file which does not already
exist. As successive records are written onto the file, its length
is extended as necessary. When a new file is created, it is useful
to immediately write an end-of-file code in the last record. Writing
the last record first forces the entire file to be allocated; making
sure that enough disk space is available. It also provides an endof-file mark. Programs which read this file may then check for this
end-of-file mark to avoid reading past the end of the data file which
results in an error.
Existing files may be enlarged by writing a new record farther
out. If the program does not know how big the file will be, it may
simply write records to the file in sequence. The file will be
automatically extended. When all the records have been written, one
final end-of-file mark can be added.
In general, all records read or written on a specific file should
be the same length, i.e., contain the same number of variables.
However, if the user is careful he may intermix records of different
lengths in a file. Suppose the following statement is executed:

and the value of N is n and the record specified by statement 100 is
of length m. The PUT statement will write m variables in the file
starting at the m*n variable. The simple rule for computing the
first variable in the file to be accessed is the record length times
(Remember the first record is record number
number.
the record
zero.)

4-23

4.3.4

Closing/Deleting Disk Files

When all work has been completed on a data file, it should be
closed with a CLOSE statement. Once the file is closed, it may not
be read or written unless it is reopened. The file does, however,
remain on the disk and is available for future use. The CLOSE
statement is followed by the internal file number to be closed (8 or
9). For example:
958 CLOSE 8

If the disk file was just created for temporary scratch use (to
pass parameters during a CHAIN, for example), it should be deleted
at the end of the program instead of closed. The UN SAVE statement is
used to delete files. For example:
1090

UNSAVE 9

The file opened on internal file number 9 is deleted from the disk.
Both CLOSE and UNSAVE may be followed by an expression equating to
8 or 9 instead of a constant.
Open disk data files are automatically closed at the end of the
program, unless the program CHAINs to another program. In this case,
all open files remain open and the new program may access them without executing an OPEN statement.
4.4

DECTAPE DATA FILES

Large permanent data files are best stored on DECtape rather
than on disk. Each DECtape holds up to 380,000 characters of information. DECtape data files may be dismounted for safekeeping,
thereby insuring their privacy. Data files on DECtape are similar
to files on disk except that they do NOT have filenames. Each reel
of DEC tape is treated as a discrete data file. When the tape is

4-24

mounted on a DECtape drive, records may be read and written directly
onto the tape.
A DECtape data file may be used by only one user at a time.

Once

a DECtape unit is assigned, a single user has exclusive access to it
until he releases it.

Each DECtape drive has a WRITE LOCK switch

which physically prevents any write operations to that unit.

If the

WRITE LOCK switch is set, programs may not write on the tape even if
the unit is assigned.
DEC tape data files may be used in a variety of ways.

Programs

which need large data files should use DECtape to avoid consuming
large disk areas.

Administrative files, such as student or employee

records, are best stored on DECtape.

Since they are removable and

can be write-locked when mounted, their use can be tightly
DECtapes are also useful for information retrieval.
be kept permanently mounted but write-locked.

controlled~

A data tape may

Individual users may

run programs which assign and query that file, then release it for
others to use.
4.4.1

DECtape File Records
Records for DEC tape data files are specified the same way as

for disk data files:

with a RECORD statement.

records apply to DECtape records.

All rules for disk

In fact, the same RECORD statement

may be used for both a DECtape and disk file.

(This is useful when

transferring a tape file to a disk file for processing.

Access to

disk data files is considerably faster than to DECtape data files.)
It is possible to specify any record length for a DECtape data
file, but a size of 43 variables is suggested, even more strongly
than for disk data files.

DECtapes are physically structured into

blocks, each of which holds exactly 43 variables.

If the record

specified by the program is, for example, 44 variables, it requires
two full blocks on the tape.

4-25

Records which are multiples of 43 variables are efficient in
utilizing DECtape space but are not efficient in speed. Such records are written in consecutive DECtape blocks. The tape unit
cannot read or write consecutive blocks without stopping the tape and
rewinding it slightly (rocking). This tape rocking also occurs when
single block records (43 variables or less) are read or written as
consecutive DECtape records.
(In this case, each DECtape file record
corresponds to a physical tape block.)
The most efficient way to utilize DECtape is to make records
43 variables in length and write them onto every tenth record in
the file (records 0,10,20, etc.). When the entire length of the
tape has been traversed (the last block of the tape is number 1473),
write next into records 1, 11, 21, etc. In this way, every record
is eventually filled. Programs which will be used repeatedly should
access the tape in this manner.
4.4.2

Opening a DECtape File

DECtape data files, like disk files, are completely separate from
the programs which use them. Therefore, the program may specify
which tape, or tapes, it will use. The OPEN statement is used for
this purpose. Since DECtape files do not have names,2 the OPEN
statement specifies the DECtape unit number to be used. It is assumed
that the proper tape reel has been mounted. If the file is to be
updated, the unit should be write-enabled. If not, it should be
write-locked. The OPEN statement is followed by the unit number to
be used (0-7).
118 OPEN a
118 OPEN 7

2It is important to note that BASIC data file DECtapes are not the
same as the file-oriented DECtapes used by COPY. There is no
directory on a BASIC DECtape file. Each tape is considered to be
one file of data.

4-26

The unit number could be an expression. Making the unit number
a variable is very useful since it is hard to predict which units
will be available at the time the program is run. When the unit
specification is a variable, the user may mount the file on any free
unit, then INPUT the number into the program.
When the OPEN statement is executed, the indicated DECtape unit
is automatically assigned to the user. It cannot subsequently be
assigned to any other user. Thus, it is possible to try to open,
hence assign, a unit which is already assigned. If, in the above
examples, units 2 and 7 were already assigned to the current user or
any other user, the program would be terminated and an error message
printed.
An alternative form of the OPEN statement allows the program
itself to handle this situation. OPEN statements may include an
ELSE clause which specifies a line number. If the OPEN statement
fails, BASIC automatically performs a GO TO to this line number.
For example:
18e OPEN 2 ELSE 900
If unit 2 is available, it is assigned and BASIC goes on to execute
the next statement. If unit 2 is not available, statement 900 is
executed next. Statement 900 could print a message and perhaps ask
for an alternate unit number.
4.4.3

Reading/Writing DECtape Files

DEC tape data files are read and written using the same GET and
PUT statements as are used for disk data files. The internal file
number is a number between a and 7, or an expression. Unlike disk
data files, DECtape data files are of a constant length equal to the
capacity of the tape. The exact number of records per reel depends
on the record size as follows:

4-27

Record Size

Tape Capacity

1-43 variables
44-86 variables
87-129 variables

1474 records
737 records
491 records

As indicated in the section on DECtape data records, a record
size of 43 variables or less is recommended since it conforms to
the physical blocking of the tapes themselves. It is also desirable
to space the records along the tape so that the tape does not waste
time rocking. The following subroutine could be used to write 1474
records on the tape in this fashion. It assumes that R is set to
zero before it is called the first time and that the unit number is
in U.
500 REM SUBROUTINE TO WRITE RECORDS ALONG TAPE
510 REM WRITES ONE RECORD EACH TIME CALLED
515 PUT U~10~R 'REMEMBER THIS INCREMENTS R
517 LET R=R+9 'SPACE OUT 10 BLOCKS
524 IF R<1414 THEN 550 'OK TO RETURN
530 IF R=1479 THEN 560 'TAPE IS FULL
540 LET R=R-1479
545 IF R>0 THEN 550
547 LET RsR+10
550 RETURN
568 STOP 'TAPE IS FULL
The following function may also be used to convert a logical
record number (0 to 1469) to a physical record block spaced along
the tape. This function does not use blocks 0-3. These blocks are,
therefore, available for a header or label. Both the subroutine
above and the function below assume a record length of 43 variables
or less.
FNC(X)

= (X-INT(X/147)*147)*10 + INT (X/147)+4

Once opened, any record on the tape may be read. The tape unit
must, however, be write-enabled if it is to be written. Trying to
PUT to a write-locked tape is an error.

4-28

4.4.4

Closing DECtape Files

Once all work on a DECtape data file has been completed it may
be closed~ Closing a file releases the tape ~~it and makes it available to other users. Thus, if the tape contains important information (and especially if it is write-enabled) the CLOSE should not be
done until the tape reel has been removed. If no CLOSE statement is
encountered in the program, the unit remains assigned after the program has finished: The DECtape unit remains assigned until a Monitor
RELEASE command is executed or the user logs out. An example of a
CLOSE statement follows:

1108 CLOSE 6

4.4.5

Using Dectape Data Files with OS/8 FORTRAN

Numeric DECtape data files written by BASIC may be read by OS/8
FORTRAN with the FORTRAN RTAPE and WTAPE subroutines, and vice-versa.
(String and Hollerith variables use different character codes.)
Thus, it is possible to use BASIC to prepare an input or update tape
for a stand-alone FORTRAN program. This provides a convenient way
to do big jobs in off-hours, without having to leave the time-sharing
mode for very long.
4.5

LINE PRINTER OUTPUT

If a line printer is available, it may be used both to list
BASIC programs and to serve as an output device for the programs
themselves. The line printer may only be u.sed by one user at a time.
The statements associated with line printer output are LLIST and
LPRINT.
LLIST is similar to the LIST command except that the program
listing is output to the line printer rather than to the Teletype.
The LLIST co~mand assumes that no other user has the line printer

4-29

assigned and responds by typing WHAT? if the line printer is not
available. After the listing is complete, the line printer is
released and is available to any user.
BASIC programs may use the line printer as an output device
during execution by means of the LPRINT statement. LPRINT is
exactly like PRINT except that the information goes to the line
printer rather than to the Teletype. All formatting conventions of
the PRINT statement are available with LPRINT. In particular,
CHR$(12) may be used to skip to the top of the next form (page).
The LPRINT statement also assumes that no other user has the
line printer assigned. However, using this statement when the line
printer is not available causes the program to terminate. Once
LPRINT successfully assigns the line printer, it remains assigned
until the program terminates.
The OPEN and CLOSE statements may be used to assign and release
the line printer. An OPEN statement with a device number of 11
assigns the line printer, or if it is not available and an ELSE
clause is specified, transfers control to the line number specified
in the ELSE clause. CLOSE 11 releases the line printer.
4.6

INTERNAL DATA CODES

Using the file I/O capabilities and the CHANGE statement, it is
possible to examine data which was written on a DECtape or disk file
by a program other than BASIC. There are two data formats: numeric
and string.
4.6.1

Numeric Data

Each numeric value in BASIC is three PDP-8 words long.
storage format for numeric data is as follows:

4-30

The

~11

.. '--____ -------J
SIGN - - - I
_ _ _ _----r+
BINARY EXPONENT

_
HIGH ORDER MANTlSSA----------~

~2LI

______________________________~
MANTISSA

~D3LI

______________________________~
LOW ORDER MANTISSA

A one in the sign bit means that the number is negative.
nent is kept in excess 200 form where:

The expo-

200 8 is 2 0
201 8 is 21
177 8 is 2- 1
The assumed decimal point is between bit 8 and 9 of word 1. Also,
the number is always normalized, meaning that bit 9 is always 1
unless the number is zero.
(Zero is represented by three zero words.)
Note that this format is the same as the format used by OS/8 FORTRAN
IIi it is not the same as FORTRAN-D format.
4.6.2

String Data

Each string variable is three PDP-8 words long. Each word contains two 6-bit bytes or characters. If a string variable is filled
by a GET from a source which was not written by a BASIC program, a
BA~IC program may examine the data in the variable by performing a
CHANGE on that variable. The six bytes will be translated as if they
were internal character codes for BASIC string characters. Table 4-1
shows how this translation interprets the 64 possible types. Note
that after such a CHANGE, the Oth element of the array contains a
count of the number of characters occurring before the first null.

4-31

TABLE 4-1
BASIC INTERNAL DATA CODES
6-Bit
Byte
Octal

Byte
Decimal

ASCII
Char.

00
01
02
03
04
05
06
07
10
11
12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

NULL
SPACE

4.7

%
&

(
)

/-'
0
1
2
3
4
5
6
7
8
9
<

=
>

6-Bit
Byte
Octal

Byte
Decimal

ASCII
Char.

40
41
42
43
44
45
46
47
50
51
52
53
54
55
56
57
60
61
62
63
64
65
66
67
70
71
72
73
74
75
76
77

.32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63

?
@

A
B
C
D
.E
F

G
H
I
J

L
M
N
0

P
Q

R
S

T
U
V
W
X
y

Z
[

\
]

ERROR MESSAGES
Most programs, especially if they are at all complex do not

execute correctly the first time they are tried.

EduSystem 50 checks

all BASIC statements when they are entered and before executing them.

4-32

If it cannot execute a statement, it informs the user by printing one
of the error messages shown in Table 4-2, followed by the line number,
if present, in which the error occurred.
In addition, the system checks for non-fatal execution errors
and notifies the user that he performed a computational range error.
When errors of this type occur, the messages shown in Table 4-3
appear, followed by the line number in which the error occurred.

TABLE 4-2
BASIC ERROR MESSAGES
Explanation

Message
ABORT

BASIC can not run for some reason.
Perhaps the user's disk quota is
exceeded.

ARRAY OR RECORD USED
BEFORE DEFINITION

The RECORD statement must occur before
any reference to it is made. A DIM
statement must occur before an array
is used.
(RECORD and DIM are placed
at the beginning of a program.)

BAD FILE FORMAT

The program specified in response to
OLD PROGRAM NAME was not acceptable
to BASIC. This is generally caused
to load a non-BASIC (FORTRAN or PAL-D)
program.

BAD FILE NAME

The file name used is not valid, e.g.,
it does not begin with a letter.

BAD SLEEP ARGUMENT

The argument of the SLEEP statement
must have a number greater than or
equal to 0, and less than or equal to
4094.

BAD VALUE IN CHANGE
STATEMENT

While performing CHANGE A TO A$, one
of the elements of the array A was
found to contain an illegal value.

CAN'T CREATE FILE

An OPEN statement tried to create a
file, but there is:
(a) no disk space
available, (b) no file name specified,
or (c) a null string has been given
as the file name:

4-33

Table 4-2 (Cont.)
Message

Explanation

CAN1T DELETE FILE

UNSAVE cannot delete a file. This is
usually due to the fact that another
user has the file open, or the file is
protected with a code >20.

CAN I T DELETE:

An attempt has been made to UNSAVE a
protected file.

name

CAN1T FIND LINE

An attempt has been made to edit a
non-existent line.

CAN1T FIND "name" IN
SYSTEM LIBRARY

The requested old file cannot be found.

CHAIN TO BAD FILE

The file specified by the CHAIN has an
invalid format:
it is not a BASIC
format file. The "PROGRAM IS ••• "
message will follow this error message.
The program name will be the name of
the bad file.

DEF STATEMENT MISSING

A function needing a DEF statement
exists in the program.

DEVICE BUSY

The user tried to OPEN DECtapes 0-7,
line printer, or paper tape punch, but
the device was unavailable, and there
was no ELSE clause in the OPEN statement.

DIMENSION TOO LARGE

Too large an array to fit in the available core.

DISK FULL

There is no more storage space on the
system disk.

DUPLICATE FILE NAME

An attempt has been made to SAVE a
program, but one with that name already
exists.

EXECUTE ONLY

An attempt has been made to list, save,
or alter a BASIC complied program.
The program can only be run.

FOR WITHOUT NEXT

There is an unmatched FOR statement in
the program.

GET BEYOND END OF FILE

Disk data file is too small to have a
record with the number specified in the
GET statement at line n.

4-34

Table 4-2 (Cont.)
Message

Explanation

GET/PUT ERROR

A hardware error occurred in GET or
PUT.
(This is usually due to a
DECtape unit being write-locked.)

GOSUB - RETURN ERROR

Subroutines are too deeply nested or
a RETURN statement exists outside a
subroutine.

ILLEGAL CHARACTER

The user attempted to use an illegal
character in, the statement being
processed.

ILLEGAL CONSTANT

The format of a constant in the statement being processed is not valid.

ILLEGAL FORMAT

The structure of the statement does
not agree with BASIC syntax.

ILLEGAL FOR NESTING

FOR-NEXT loops are too deeply nested
or NEXT appears before FOR.

ILLEGAL INSTRUCTION

A statement was used which is not
one of the legal BASIC statements.

ILLEGAL LINE NUMBER

The format of the line number being
used in a GOTO or IF statement is
not acceptable. A line number has
been typed which is not between 1
and 2046, inclusive.

ILLEGAL OPERATION

The expression being processed does
not agree with the BASIC rules (this is
probably due to unmatched parentheses).

ILLEGAL SYNTAX

The expression in a statement does
not agree with the BASIC syntax.

ILLEGAL VARIABLE

An illegal variable was used in an
array.

IMPROPER ACCOUNT # ABORT +BS

A user logged in under account numbers
1 (system account) or 2 (system library) and tried to run BASIC. This
is prohibited.

IMPROPER DIM OR RECORD
STATEMENT

Syntax error in DIM or RECORD statement, or an array name that was previously dimensioned is reused.

4-35

Table 4-2.
Message

(Cont.)
Explanation

INVALID DEVICE NO.

The device number in the file I/O statement is not between 0 and 11 inclusive,
(or X and 11 inclusive where X is a
number set by the system manager) •

INVALID RECORD NO.

The record number must be a number
which is greater than or equal to 0
and less than or equal to 4095. For
DECtape I/O the maximum record number
is limited further by the DECtape size.

LINE TOO LONG

Too much has been typed.

MISUSE OF CHR$

The CHR$ function was used in an invalid manner. CHR$, like TAB, can
appear only in PRINT statements.

MISUSED TAB

The TAB function was used in an invalid manner. TAB can appear only in
PRINT statements.

MORE?

Not enough values have been entered in
response to an INPUT command. The rest
of the values may be entered.

NEXT WITHOUT FOR

The NEXT statement indicated has no
preceding FOR statement.

NO END STATEMENT

All programs must have an END statement.

ON INDEX OUT OF RANGE

The 'value of the index is less than
one, or greater than the number of
statement numbers.

OUT OF DATA

An attempt was made to READ more data
than was supplied by the user.

PROGRAM IS "progname"

This message may immediately follow
an· error message, to identify the
current program in a series of CHAINed
programs. If there is no CHAIN, this
message will not occur.

PROGRAM NOT FOUND

The file which the user tried to access
with a CHAIN statement does not exist
in his disk area. The PROGRAM IS
message will also occur.

PROGRAM TOO LARGE

The program is too large to be executed.
Make it smaller.

4-36

Table

(Cant. )

Message

Explanation

STACK OVERFLOW

The user programmed a situation in
which the expression is too complicated to be executed.

SUBSCRIPT ERROR

A negative subscript was used for an
array.

SYSTEf.l I -0 ERROR

BASIC was unable to perform the desired
disk I/O.

TIME LIMIT EXCEEDED

The number of statements executed by
a job has exceeded the maximum established by the system manager. Generally, some error was made and the program is caught in a loop.

TOO MUCH INPUT, EXCESS
IGNORED

Too many values have been entered in
response to an INPUT command.

UNDEFINED LINE NUMBER

The line number appearing in a GOTO or
an IF-THEN statement does not appear
in the program.

UNOPEN DISK UNIT

The user tried to do a GET, PUT, or
UNSAVE to device 8 or 9, without a
file being previously opened on the
device

WHAT?

The editor cannot understand the
command given.

4-37

TABLE 4-3
NON-FATAL EXECUTION ERRORS
Message

Explanation

An illegal character or constant has
been typed in response to an INPUT
statement. The input is requested
again.

An attempt was made to compute the
logarithm of zero or a negative number.
Zero is used for the result.

Overflow - the result of a calculation
was too large for the computer to
handle. The largest possible number
is used for the result.

An attempt was made to raise a negative
number to a fractional power. The
absolute value of that number raised to
the fractional power is used.

An attempt was made to compute the
square root of a negative number. The
square root of the absolute value is
used for the result.

Underflow - the result of a calculation
was too small for the computer to
handle. Zero is used for the result.

Zero divide - an attempt was made to
divide by zero. The largest possible
number is used for the result.

4-38

TABLE 4-4
EDUSYSTEM 50 BASIC LANGUAGE SUMMARY
Statement

Format

Explanation

InEutLOutEut Statements
CLOSE
DA,TA

CLOSE f
DATA nl,n 2 , .•• nn

GET

GET f,l,r

Read record r from file f into the variables
in line 1.

INPUT

Get vI through vn input from .the terminal.

LINPUT

INPUT VI, 2, · · · v n
LINPUT v$1,v$2, ..• v$n

LPRINT

LPRINT el,e2,···e n

Print values of specified text or expressions
on line printer.

OPEN

OPEN f,n$

Open a file named n$ as file nwnber f ..

OPEN-ELSE

OPEN f ELSE n

PR.INT

PRINT el,e2, ... e n

Open a file, go to line n if unavailable.
Print values of specified text, vaJr iables , or
expressions.

PUT

PUT f,l,r

Write record r, formatted as in line 1, into
file f.

READ

Read variables vI through ~ from DA~rA list.

RESTORE

READ vl,v2, ... v n
RESTORE

Reset DATA pointer to beginning value ..

RESTORE*

Reset DATA pointer for numeric data only.

RESTORE$

Reset DATA pointer for character string data
only.

UNSAVE

UNSAVE f

Delete file f from disk storage.

w
\.D

Close file f.
Numbers n 1 through nn = variables in READ
statement.

Get long character string input from
(up to 50 characters).

termin~l

Table 4-4.

(Cont.)
Explanation

Format

Statement
Transfer of Controls
GOTO

GOTO 1

Transfer control to line number 1.

IF-GOTO

IF el r e2 GOTO 1

If relationship r between el and e2 is true,
transfer control to line number 1.

IF-THEN

IF el r e2 THEN 1
ON e GO TO 1 1 ,1 2 , ... 1 3

Same as IF-GOTO.

ON-GOTO

Computed GOTO.

LooEs and SubscriEts

FOR-TO-STEP

DIM v(dl), v(d l ,d 2 )
FOR v=el TO e2 STEP e3

NEXT v

DIM
~

Dimension subscripted variables.
Set up program loop. Define v values beginning
at el to e2' incremented by e 3 •
Terminate program loop.
(Increment value of v
until v>e2.)

Subroutines
GOSUB

GOSUB 1

RETURN

STOP

Enter subroutine at line 1.
Return from subroutine to statement following
GOSUB statement.
Transfer control to END statement.

Others
CHAIN

CHAIN n$

CHANGE

CHANGE vI TO v 2

DEF

DEF FNA(x)=f(x)

END

Link to next program.
Change character string to array of character
codes or vice versa.
Define a function.
End of program.

Table 4-4.
Statement

(Cont.)

Format

Explanation

LE'l~

LET v=f

Assign value of formula f to variable v.

RANDOMIZE

Randomize random number routine.

REMARK

REM text

Insert a remark or corrunen t: •

SLEEP

SLEEP n

Cause program to pause for n seconds.

Edit/Control Corrunands
BYE

BYE

Leave BASIC Monitor.

CA,]~ALOG

CAT

List names of programs in storage area.

COr-1PILE

COM name

Compile program in core and save it on disk.

CTRL/C

Stop program execution; return to edit phase.

DEIJETE

DEL n

Delete line n.

DEL n,m

Delete lines n through m, inclusive.

EDI n

Search line n for character c.

EDIT

KEY

Return to keyboard mode after TAPE.

LIST

List entire program in core.

LIST n

List line n only.

LIST n,m

List lines n through m, inclusive.

LLIST

List program on line printer.

NE~v

NEW

Clear core, request program name~

OLD

Clear core, bring program to core from
storage area.

Table 4-4.

(Cont.)

Format

Statement

'Explanation

REPLACE

REP
REP name

Replace old file on disk with version in core.
If name is not specified, old name is retained.

RUN

Compile and run program in core.

SAVE

SAVE name

Store program named on storage device.

SCRATCH

SCR

Erase current program from core.

TAPE

TAP

Read paper tape; suppress printing on Teletype.

UNSAVE

UNSAVE name

Delete program named from storage device.

ABS

ABS(x)

Absolute value of x.

ATN

ATN(x)

Arctangent of x

COS

COS (x)

EXP

EXP(x)

Cosine of x (x in radians).
eX (e is approximately 2.7182818).

INT

INT(x)

Greatest 1nteger of x.

LOG

LOG (x)

Natural logarithm of x.

RND

RND(x)

Random number.

SGN

SGN(x)

Sign of x
if zero).

(+1 if positive, -1 if negative, 0

SIN

SIN (x)

Sine of x

(x in radians) .

SQR

SQR(x)

Square root of x.

TAN

TAN (x)

Tangent of x

TAB

TAB (x)

Controls printing position on terminal or line printer.

FIX

FIX (x)

Truncates decimal portion of x.

CHR$

CHR$(x)

Converts character code to character. Used
only with the PRINT or LPRINT statements.

Functions
,J::.

,J::.
N

(result in radians).

(x in radians).

CHAPTER 5
FOCAL

FOCAL (FOrmula CALculator) is an on-line, interactive, service
program for the PDP-8 family of computers, designed to help scientists,
engineers, and students solve numerical problems.

The language con-

sists of short imperative English statements which are easy to learn.
FOCAL is used for simulating mathematical models, for curve plotting,
for handling sets of simultaneous equations, and for many other kinds
of problems.
To call FOCAL, type:

.R FOCAL
FOCAL enters its initial dialogue, and asks if its extended functions
are to be retained.

The extended functions are exponential, sine,

cosine, arctangent, and logarithm.

If the FOCAL program to be run

uses any of these functions, the user responds YES.

If not, the

user responds NO to free more space for the user program.

Without

the extended functions, there is room for approximately 1100 characters of program.

If the extended functions are retained, there is

room for approximately 735
5.1

characters.

USING FOCAL COMMANDS
Whenever FOCAL prints an

asterisk, it is in command mode, and

the user may type any of the FOCAL commands in response to the
asterisk.

FOCAL commands may be direct or indirect.

A direct com-

mand is typed directly after the asterisk and is executed immediately.
The format for direct commands is:

5-1

* COMMAND
An indirect command is always identified by a line number.
Indirect commands are not executed until program control passes to
the line number associated with the command.

The format for indirect

commands is:
*GG.ss COMMAND
When the user is typing indirect commands, he may use any line
number in the range 1.01 to 31.99, except those ending in.OO.
Numbers such as 1.00 or 31.00 are illegal as line numbers; they are
used to identify an entire group of line numbers.

Line numbers are

typed in the format:
GG.ss
where GG is the group number and ss is the step number.

It is not

necessary to type two digits after the decimal; e.g., 2.1 is equivalent to 2.10.
All FOCAL commands must be followed immediately with a space.
All FOCAL command lines must be terminated with the RETURN key.
5.2

FOCAL OVERVIEW
FOCAL consists of 12 commands which are all the beginner

needs to write programs.

FOCAL commands may be typed in their

entirety or abbreviated.

The FOCAL commands are:

5-2

Command
ASK

Explanation
Used to assign values to variables from

the keyboard.
COMMENT or CONTINUE

Used for comments or non-executable
program steps.

Used to cause a specific line or group
of lines to be executed.

ERASE or ERASE ALL

Used to erase part of a program or an

entire programQ
FOR

Used to increment a number and execute
a user-specified command for each value
of the number incremented.

GO or GOTO

Used to direct program control to the
lowest line number, or to some specific
line number.

Used to direct program control conditionally after a comparison.

MODIFY

Used to edit words or characters on a
program line.

QUIT

Used to halt program execution and
return control to user.

RETURN

Used to terminate DO routines.

SET

Used to define variables and evaluate
expressions.

TYPE

Used to print text, results of calculations, and values of variables.

These commands are explained in detail with actual computer
output in this section.

For the convenience of the user, a detailed

FOCAL command summary is included in Table 5-1.
5.3

NUMBERS
A FOCAL number may be any decimal number between _10

615

and

Numbers may be written signed (+ or -) -or unsigned, either

with a decimal point and a fractional part or in exponential format
(see Data Formats) with a mantissa and exponent.
n~~ers

In FOCAL, all

are internally represented in exponential format, retaining

5-3

up to six significant digits. If more than six digits are specified,
the number will be rounded to six digits. The following numbers are
identical in FOCAL:
60
60.00

6El
600E-l
60.00003

5.4

VARIABLE NAMES

FOCAL variable names may consist of either one or two characters.
The first character must always be alphabetic; however, it cannot be
an F because FOCAL reserves that character for function names (see
FOCAL Functions). The second character may be either alphabetic or
numeric. The user may write variable names consisting of more than
two characters, but FOCAL uses only the first two characters to
l
identify the variable.
Therefore, the first two characters must be
unique •
• SET A-S6789
.SET B=1234S6
*SET Cla15
*SET C2=30
*SET DEPTH=10
.SET DISTANCE-Cl+C2
Variables may also be subscripted. For a discussion of what
subscripted variables are and how they are used, see Subscripted
Variables.

lA variable is represented internally as a binary fraction with an
exponent. See Data Formats.

5-4

5.5

ARITHMETIC OPERATIONS

To print the results of arithmetic calculations, the user types
the FOCAL command TYPE followed by a space and the data to be calculated. Then he presses the RETURN key: and FOCAL prints the
answer. For example:
*TYPE 6+10-3-1
~

12e0000*

The above example shows two of the arithmetic operations (+ and
-) performed by FOCAL. Arithmetic operations are performed from
left to right except when the operation to the right has priority or
when enclosures are used.
(See Enclosures.)
*TYPE 6+5; TYPE 5+2-31 TYPE 10-6

11.0000=

4.0000=

4.0000*

NOTE
Several commands may be typed on the same
line if they are separated by semi-colons
(i). This is true for all FOCAL commands
except the LIBRARY commands.
Unless indicated otherwise, FOCAL mathematical computations
retain an accuracy of six significant digits.
5.5.1

Priority of Arithmetic Operations
The FOCAL arithmetic operations priorities are:
First priority - exponentiation (t)2
Second priority = multiplication (*)

2When exponentiation is performed by FOCAL, the power to which a
number is raised must be a positive integer. If a calculated
exponent exceeds the limits of size, no error message is given.
The result will go to zero.

5-5

Third priority - division (I)
Last priority - addition (+), subtraction (-)
When FOCAL evaluates an expression which includes several arithmetic
operations, the above order of priority is followed.

Therefore,

FOCAL evaluates
*TYPE 25+5*2+5

to have a value of

because multiplication (*) has a higher priority than addition (+).
5.5.2

Enclosures
The order of executing arithmetic operations is also influenced

by enclosures.

Three kinds of enclosures may be used with FOCAL:
3
parentheses ( ), square brackets [ ] , and angle brackets<>. FOCAL
treats them all the same.

For example, the result of the expression:

*TYPE (A+B)*cC+D>*CE+Fl

is the same as the result of:

If the expression contains enclosures within enclosures (called
nesting), FOCAL executes the contents of the innermost enclosures
first and works outward.
*TYPE (5*<2+3>·(5)t2
= 400.0000*
3

[ and]

are typed by SHIFT/K and SHIFT/M, respectively.

5-6

5.6

INPUT/OUTPUT COMMANDS

5.6.1

TYPE Co~~and

The TYPE command is used to print results of calculations,
values of variables, text or character strings, and variable tables.
TYPE may also be used to print combinations of text and variables.
Example I - Result of a Calculation:
*TYPE 1+1
=-

2.0000*

Example 2 - Value of a Variable or Variables:
*SET N=S+S; SET M=30

*TYPE N"M
=

10.0000=

30.0000*

Example 3 - Text:
*TYPE "TH!S IS A LINE OF TEXT"" 14
THIS IS A LINE OF TEXT

*
Example 4 - Variable Tables:
*TYPE S
NI(00)=
MICe0)=

•

The user may command FOCAL to print all of the user-defined
variables (variable table) by using the TYPE command and a dollar
sign ($).

exclamation mark

I I \
\ • I

causes a carriage return and line feed.

5-7

If a variable consists of only one letter, an at sign (@) is
inserted as a second character in the variable table printout, as
shown in the example above .

• SET N=25

.TYPE UN IS".N
N 15=

25.0000*
NOTE
Any variable, constant, or expression in
a TYPE or ASK command must be followed by
a comma, semicolon, or carriage return.

S.6.2

ASK Command
The ASK command is normally used in indirect commands to enable

the user to input numerical data during the execution of his program.
The ASK command is similar to the TYPE command in form, but only
single variable names, not expressions, are used; and the user types
the values in response to a colon (:) printed by the ASK command.

When FOCAL encounters line 11.99 in the above example, it prints a
colon and waits for the user to type a value (in any format) and
a terminatorS for the first variable.

This process continues until

all the variables in the ASK command have been given values.
The value is assigned to the variable when the user types a
terminator; so any time before the terminator is typed, the value
can be changed.

If the user types back arrow (-or SHIFT/a)

immediately after the value and before he types a terminator, he can
then type the correct value and a terminator.

STerminators are SPACE, comma, ALT MODE, and RETURN keys.
user types the RUBOUT key, it is ignored.

S-8

If the

*ASK X.. y .. Z
User typed 5 and RETURN key.
User typed 6 and RETURN key.
--User typed
7 and RETURN ,Key.

: 5

as"7

*TYPE x .. !.Y.!.Z
•
5.0000
=
6@0000
•
7.0000*

The ALT MODE key is a special non-spacing terminator which
enables the user to have a previously assigned value unchanged.

*ASK X.. y .. Z
:3
User typed ALT MODE because he did
not want to change the value of Y.

::12
*TYPE X .. ! .. y .. ! .. Z

3e0000

:II

6.0000
12.0000*

5.6.2.1

Text Output with ASK -- The ASK command, just as the TYPE

command, may be used to print text.

Carriage return and line spacing

are controlled the same as with the TYPE command (see Data Formats) .
*ASK "WHAT IS YOUR AGE?" AGE
WHAT IS YOUR AGE?:19

*
The word following the text in the command line (AGE, in this
example) is the variable.
5.7

COMPUTATIONAL COMMAND

(SET)

The SET command enables the user to assign a numerical value to
a variable and store both the value and the variable.
Then, when he
6
uses the variable in an expression , FOCAL automatically substitutes
the numerical value that the user previously specified:

6 An expression is a combination of arithmetic operations or functions
which may be reduced to a single number by FOCAL.

5-9

*SET E=2.71828
*SET PI=3.14159
*TYPE "PI TIMES E.... PI.E
PI TIMES E8.5397*
The value of a variable may be changed at any time by another SET
command .
• SET A1=3+2
*SET Al=Al+l
.TYPE Al
6.0000.
5.8
5.8.1

CONTROL COMMANDS
GO or GO TO Command

The GO command causes FOCAL to go the lowest numbered line in
the program and begin executing the indirect commands .
• 1.1 SET A-I
*1.3 SET B=2
*1.5 TYPE A .. S
*GO

1.0000=
In the above example the GO command caused execution to begin at line
1.1.
The GOTO command causes FOCAL to go to a specific line in the
program and begin executing the indirect commands in ascending line
number order .

• ERASE
*1.1 SET A=1
.1.3 SET B=2
*1.5 TYPE A.. B
*GOTO 1.3
0.0000=

2.0000*

5-10

In the preceding example, A and B are equal to zero at the start
of the program. The ERASE and ERASE ALL commands are used to ensure
that all variables are equal to zero until they are assigned a specific value. Since the GOTO command causes program execution to begin
at line 1~3: line 1:1 is never executed and A is not set to 1.
5.8.2

IF Command

The IF command is a conditional command used to transfer program
control after a comparison. The normal IF command format is:
IF space (expression) linel, line2, line3
The expression or variable is evaluated, and program control is
transferred to the first line number if the value of the expression
is less than zero, to the second line number if the value is zero, or
to the third line number if the value is greater than zero.
The program below transfers control to line number 2.1, 2.3, or
2.5, according to the value of the expression in the IF command.
*2.1 TYPE "LESS THAN ZERO";QUIT
*2.3 TYPE "EQUAL TO ZERO";QUIT
*2.5 TYPE "GREATER THAN ZERO"; QUIT
*IF (25-25)2.1,2.3,2.5
EQUAL TO ZERO*
5.8.2.1 IF with Less Than Three Line Numbers -- The IF command format
can be altered to transfer program control to one or two lines. For
example, if a semicolon or a carriage return is immediately after the
first line number, control goes to the first line number if the value
of the expression is less than zero. If the value is not less than
zero, control goes to the next sequential command. For example:
*2.20 IF (X) 1.a;TYPE "Q"

5-11

When line 2.20 is executed, program control goes to line 1.8 if X
is less-than zero.

If X is not less than zero, Q is typed.

If a semicolon or a carriage return follows the second line
number, control goes to the first or second line number, depending
upon whether the value of the expression is less than
to zero.

~ero

or equal

If the value is greater than zero, control goes to the next

sequential command.

For example:

*3.19 IF (B)I.8~1.9
*3.20 TYPE B
If B is less than zero, control goes to line 1.8; if B equals
zero, control goes to 1.9; and if it is greater than zero, control
goes to the next sequential command, in this case line 3.20, and the
value of B is printed.
5.8.2.2

Arithmetic Comparison with IF Command -- The IF command can

be used with all the arithmetic operations of FOCAL.
Example 1 - Addition:

Example 2 - Subtraction:

*5 • 16 IF (A -B ) 1 .6 J TYP E "X"
Example 3 - Division:

*3.10 IF (M/N>5.5.5.6
*3.15 TYPE "GREATER THAN ZERO"
Example 4 - Multiplication:

*7.20 IF (P*I)8.1

* 7.25 TYPE P*l
5-12

Example 5 - Exponentiation:

5.8.3

DO Command

The DO command is used to make subroutines of single lines or
groups of lines. Control is returned to the line following the DO
corr~and after the subroutine is executed.
*1.1 SET A-l1SET B=2
*1.2 TYPE "STARTING"
*1.3 DO 3.2
*2.1 TYPE "FINISHED"
*3.1 SET A=3JSET 8=4
*3.2 TYPE A+B
*GO
STARTING:
3.0000FINISHED=

7.0000*

If the user types a command such as DO 3, the DO command treats
the group of program lines beginning with 3 as a subroutine. Control
proceeds in ascending order through the group numbers until the end
of the group is reached, or until a RETU&~ command is executed.
5.8.3.1 Nested DO -- DO commands may be nested as shown in the
following example:
* 1 .1 TYPE "BEGIN"~!
* 1.2 DO 2
* 1 .3 TYPE .. END .. ~!;QUIT
*
*2.1 DO 5.1; TYPE A~!
*2.2 DO 5.2; TYPE A~l\1
*2.3 DO 7.5; TYPE A~!
*
* 5.1 SET A=1
*5.2 SET A=2
*
*7.5 SET A=3
*GO
BEGIN
=
1 .0000
= 2.0000
=
3.0000
END

5-13

The number of nested DO commands is limited only by the amount
of core memory available after storage is allocated for program and
variables.
5.8.4

RETURN Command
The RETURN command is used to exit from a DO subroutine.

When a

RETURN command is encountered during execution of a DO subroutine,
the program exists from its subroutine status and returns to the
command following the DO command that initiated the subroutine status.
5.8.5

QUIT Command
When the QUIT command is executed, FOCAL prints an asterisk and

returns to command mode.
5.8.6

FOR Command
The FOR command is used to set up program loops and iterative

procedures.

The general command format is:

*FOR A = B,C,D; commands
*FOR A = B,D; commands
The variable A is initialized to the value B, then the command
or commands following the semicolon are executed.

When the commands

have been executed, the value of A is incremented by C and compared"
to the value of D.

If A is less than or equal to D, the command

after the semicolon is executed again.

This process is repeated until

A is greater than D, at which time FOCAL goes to the next sequential
line.

The command or commands will always be executed at least once.

5-14

A must be a single variable. S, C, and D may be expressions,
variables, or numbers.
If the value C is omitted, it is assumed that
the increment is one.
If C and D are omitted, the FOR command is
handled like a SET command and no iteration is performed.

command may be used with a DO command and nested:
5.8.6.1

FOR with a DO

*ERASE ALL
*1.1 FOR X=I~1~5; DO 2
*1.2 QUIT

*2.1 TYPE r~"
X"~X
*2.2 SET A=X+100
*2.3 TYPE !~..
A"~A
*GO
X=
A=
X=
A=
X=
A=
X=
A=
X=
A=

5.8.6.2

1 .0000
101 .0000
2.0000
102.0000
3.0000
103.0000
4.0000
104.0000
5.0000
105.0000*

Nested FOR and DO

* 1 .1 FOR Z=I~3; TYPE
1.2 TYPE !
* 1 .5 FOR A=1~3; DO 3
1 .7 QUIT

. A

*
*
** 3.1 FOR 8=1.3; DO 4
*
*4.1 FOR C=I.3; TYPE %1,A.8.C,"
*4.2 TYPE
*GO

A B C
= 1= 1= 1
= 1= 2= 1
= 1= 3= 1
= 2= 1= 1
= 2= 2= i
= 2= 3= 1
= 3= 1= 1
= 3= 2= 1
= 3= 3= 1
*

A B C
= 1= 1= 2
= 1= 2= 2
= 1= 3= 2
= 2= 1= 2,...
= 2= 2= c:;
= 2= 3= 2
= 3= 1= 2
= 3= 2= 2
= 3= 3= 2

..
..

A 8 C
= 1= 1= 3
= 1= 2= 3
= 1= 3= 3
= 2= 1= 3
:: 2= 2= 'l
w
= 2= 3= 3
= 3= 1= 3
= 3= 2= 3
= 3= 3= 3
S-!~

A FOR

Another way of handling the same program is:
*1.1 FOR Z=113;TYPE" ABC ..
*1.2 FOR A=113JFOR B=113JTYPE !;FOR C=I,3;TYPE 11,A,S .. C....
*GO
5.8.6.3

Subscripted Variables -- Variables may be further identified

by subscripts which are enclosed in parentheses immediately following
the variables.

For example:

*SET AB(0)=5
*SET AB(I>=10
*SET AB(2)=15
*SET AB(3)=20
*SET AB(4)=25
*SET AB(5)=30
*FOR X=0" 5; TYPE ABCX),,!
= 0.500000E+01
= 0.100000E+02
= 0.150000E+02
= 0.200000E+02
= 0.250000E+02
= 0.300000E+02

In the above example, subscripts are used to set up an array
called AB.

Any element in the array can be represented by a sub-

script in the range 0 to 5.
has a subscript of O.
or an expression.

The first element in an array always

A subscript may be a number, another variable,

If it is a number, it must be in the range

~2047.

In order to be properly represented by the TYPE $ command, subscript
numbers must be positive integers in the range from 0 to 99.

The

TYPE $ command will print subscripts greater than 99 as two random
characters, although their contents will be correct as assigned by
the program.

5-16

5.8.7

COMMENT or CONTINUE Command

The COMMENT or CONTINUE command (abbreviated as C) causes the
program line to be ignored by FOCAL. The user may use the C corrmand
to insert comments into the program, or he may use the C command line
as a non-executable program step. In either case, program lines
beginning with C are skipped when the program is executed. However,
comments are printed in response to a WRITE command.
*ERASE ALL
*1.1 C INITIALIZE VARIABLES
*1.2 SET A=5
*1.3 SET B=6
*1.4 SET C=1

*
*2.1
C PERFORM CALCULATION
*2.2 TYPE A+8+C
5.9

EDIT COMMANDS

5.9.1

WRITE or WRITE ALL Command

The ~~ITE or WRITE ALL command causes FOCAL to print a program
line, a group of lines, or an entire indirect program on the terminal.
*WRITE 2.1
*WRITE 2
*WRITE

Print a single line.
Print a group of lines.
Print an entire program.

Once the program is completed, the user may want to save it by
putting it on paper tape. The procedure for saving a FOCAL program
on-line is as follows:
1.

Make sure FOCAL is in command mode.

2.
3.

Type WRITE.
Set low-speed punch to ON position.

Type RETURN key.

5-17

FOCAL will punch the entire program onto the paper tape and simultaneously print it on the terminal.
Paper tapes may be read in from the Terminal Reader by following
these instructions.
1)

Make sure FOCAL is in command mode.

Place tape in Reader (Reader off).

Type CTRL/R.

Turn Reader on.

Turn Reader off when the tape reaches the Trailer.

Type CTRL/T.

Paper tapes may also be punched in the following manner.

5.9.2

Turn Terminal offline to Local.

Turn punch on.

Hold the REPEAT, CTRL, and SHIFT keys down. Now press the P
and hold all four keys down until four or five inches of
Leader are punched. Release the repeat key first.

Turn off the punch and return the Terminal to the line
position.

Type CTRL/R, and turn the punch on.

Type W A, followed by a carriage return (this will not echo
on the terminal)·.

When the tape is finished punching, turn the punch off,
and type CTRL/T.

Repeat steps 1, 2, 3, and 4 for making Trailer.
ERASE and ERASE ALL Commands

The ERASE command deletes symbolic names, lines, or groups of
lines.
*ERASE
*ERASE 2.2
*ERASE 2

Delete all names defined in symbol table.
Delete line 2.2.
Delete all lines in group 2.

5-18

The user can check to see if the line(s) has been deleted by
typing the WRITE command after the ERASE command.

This is a useful

procedure for checking co~uands and also for obtaining a clean print~
out of the current program.
The ERASE ALL command deletes the entire indirect program.

is good programming practice to type ERASE ALL before starting to
type a new program.

The ERASE ALL command is generally used only with

direct commands because it returns control to command mode upon
completion.
5.9.3

MODIFY Command
The MODIFY command is used to change characters within a line

without changing the entire line.

The format for MODIFY is:

MODIFY line number RETURN key Search character
The search character is not printed.

After the user has typed

the line number, PETURN key, and search character, FOCAL prints
the contents of the specified line until it encounters the search
character.

When the search character is read and printing stops,

the user has anyone or more of the following options:
1.

Type new characters in addition to those already printed.

Type a form feed (CTRL/L). This causes the search to
proceed to the next occurrence, if any, of the search
character.

Type CTRL/BELL. The user can then change the search
character he specified in the MODIFY command.

Type the RUBOUT key. This causes FOCAL-to delete a
character, starting with the last character printed and
deleting one character to the left each time RUBOUT is
typed.

Type the back arrow (-) key. This causes FOCAL to delete
everything between the back arrow and the line number.

5-19

Type the RETURN key.
This causes FOCAL to terminate the
line at that point, deleting everything to the right.

Type the LINE FEED key. This is normally done after the
user has exercised one or more of the above options. After
the user has modified the line, he may type LINE FEED and
cause the remainder of the line from the search character
to the end to be printed and saved.

*7.01 JACK AND BILL W$NT UP THE HILL
*MODIFY 7.01
JACK AND B\JILL W$\E
NT UP THE HILL
In the above example, B was typed as the search character for
line 7.01.

(Note that the search character did not print.)

FOCAL

stopped printing when it encountered the search character (B), and
the user typed the RUBOUT key (\) to delete the B.
the correct letter J.

Then he typed

Next he typed CTRL/BELL and the $ key to

change the search character.

FOCAL continued to print the line

until the new search character was encountered.

The user typed

RUBOUT to delete the $ and then typed the correct character (E).
He then typed the LINE FEED key and the remainder of the line was
printed.
CAUTION
When any text editing is done, the values
in the user's symbol table are reset to
zero.
If the user defines his symbols in direct statements and then
uses a MODIFY command, the values of his symbols are erased and
must be redefined.

However, if the user defines his symbols by

means of indirect statements prior to using a MODIFY command, the
values will not be erased because these symbols are not entered in
the symbol table until the statements defining them are executed.
Notice in the example below that the values of A and B were set using
direct statements. However, typing the lines 1.1 through 1.3 reset
these values to zero.

5-20

*ERASE, ALL
*SET A=l
*SET B=2

* 1.1 SET C;;:3
* 1.2 SET D=4
*!e3 T¥PE A+B+C+D;
*GO
= 0.700000E+01
C@(00)= 0.300000E+01
D@(00)= 0.400000E+01
A@(00)= 0.000000E+00
B@(00)= 0.000000E+00

TYPE $

*
5.10

LIBRARY COMMANDS
In addition to the basic FOCAL commands, there are two special

commands to perform the library functions:
data from the system disk.

All commands following the LIBRARY com-

mand on the same line are ignored.
6 characters long.

storing and retrieving

Names of files may be from 1 to

Only alphanumeric characters, letters, and num-

bers should be used in file names.

The library commands, like other

FOCAL coromands; may be abbreviatede
5.10.1

LIBRARY SAVE Command

This command copies the current program into the user's area on
disk and gives it the name specified.

For example, the command;

*L 5 TRUE

will cause the current program to be stored on disk under the name
TRUE.

The program will also remain in the user's area.

5-21

5.10.2

LIBRARY CALL Command

This command copies the named program from disk into the user's
area.

For example, the commands:
*L C TRUE

*w
will cause the program TRUE to be recalled from the disk into the
user's area and listed on the terminal.
the user's area will be erased.

Any program currently in

The program TRUE can then be

executed with a GO command.
If the LIBRARY CALL command is given a line number and stored,
it must have at least one numbered command following it.

In this

case, the LIBRARY CALL command will cause the named program to be
called into the user's area and executed as if GO had been typed.
For example:
*3.10 L C TR~E
*3.11 C
If the above commands are included in a program, they will
cause TRUE to be brought in and executed at that point.

If there

are lines beyond 3.11 remaining to be executed, they will be deleted.
This procedure allows the user to chain FOCAL programs as in BASIC.
5.10.3

Error Messages with Library Commands

When the LIBRARY commands are used, five errors are possible.
These are also listed in the error code summary in Table 5-3.

5-22

Message

Explanation

?30.71

The command appeared to be a LIBRARY
command but was not, for example:
LIBRARY OPEN
No action is taken; the command should
be retyped.

5.11

? 30.< 0

Either an unacceptable file name was
specified or no name was specified
where one was required.

?31.42

The file name specified does not match
any name currently in the user's disk
directory. This error will only occur
with the LIBRARY CALL command.

?31.43

There is already a program with the
specified name in the directory. This
error will only occur with the LIBRARY
SAVE COMMAND.

?31.44

This user's disk directory is full.
The current program cannot be saved
until others have been deleted. This
error will only occur with the LIBRARY
SAVE command.

ESTIMATING PROGRAM LENGTH
FOCAL permits approximately 1100

(decimal) locations to be

used for the user program and variables without the extended math
functions, and approximately 735

locations with the extended func-

tions (sine, cosine, log, exponential, etc.).

Since FOCAL requires

five locations for each variable stored in the variable table and
one location for each two characters of stored program, the approximate length of a program may be determined by the formula:
Length of program = 5S + ~ + 2L
where

5-23

S = number of variables
C = number of characters in program
L = number of lines
If the total program area or variable table area becomes too
large, FOCAL prints an error message (06.54 or 10.:5).

The following

routine allows the user to find out how many core locations are left
for his use.
*ERASE
*FOR 1=11300; SET ACI)=1
?06.54
(Disregard error code)
*TYPE %4II*5I n LOCATIONS LEFT"
795LOCATIONS LEFT*

5.12

DEBUGGING

5.12.1

Using the Error Diagnostics

Whenever FOCAL detects an illegal command or improbable condition within a user's program, the execution of the program stops and
an error message is printed in the form ?XX.XX@GG.ss, where ?XX.XX
is the error message and GG.ss is the line at which the error
occurred.

(See Table 5-3 for the complete list of error messages.)

Depending upon the type of error detected, the user may ignore
the error message or make program changes before continuing.

For

example, if the user types CTRL/C to terminate a loop, the error
message ?01.00 is printed and program control goes to command mode;
so, in this case, the user ignores the message and types his next
command.

If a program stops and the message ?03.05 is printed, the

user must examine his program to determine which command line is
wrong.

In the following program, line 1.3 contains the instructions

to transfer to a nonexistent line number.

5-24

*ERASE ALL

*1.1 SET A'=2; TYPE .. A.... A.. !
*1~2 SET 8=4; TYPE nBn .. B.. !
*1.3 GOTD 1.01

*1.4 TYPE .. A+B .... A+B
*GO

2.0000

4.0000

?03.05

@ 01.30

*
5.12.2

Using the Trace Feature

The trace feature is used to check the logic in part of a FOCAL
program.

To implement the trace feature, the user inserts a question

mark (?) into a command string at any point.

FOCAL prints each

succeeding character as it is executed until another question mark is
encountered or until the program returns to command mode=

For

example, the trace feature is used to print parts of 3 lines in the
following program:

*ERASE ALL

* 1 • .1 SET A= 1

*1.2 SET B=5
*1.3 SET C=3
*1.4 TYPE ?A+B-C? .. !
*1.5 TYPE ?B+A/C? .. !
*1.6 TYPE ?B-C/A?
*GO

A+B-C=

B+A/C=
B-C/A=

3.0000
5.3333
2.0000*

NOTE
The WRITE command disables the trace feature.
5.13

FOCAL FUNCTIONS
The FOCAL functions improve and simplify arithmetic capabilities.

In general, the FOCAL functions may be used anywhere a number or a
variable is legal in a mathematical expression.

A standard function

call consists of three or four letters beginning with the letter F

5-25

and followed by an expression in parentheses.

The FOCAL functions

are summarized in Table 5-2.
The functions must be. used with a legal FOCAL command.
cannot be used alone as commands.

They

For example:

*SET Z=A+FSQT(FSINCX»

Within a normal range of arguments, at least five significant
digits of accuracy may be expected for the trigonometric, exponential,
and logarithmic functions.

The following functions are available to

FOCAL users.
5.13.1

Sine Function (FSIN)

The

Sil!2

function (FSIN) is used to calculate the sine of a user-

specified angle in radians.

The format for FSIN is:

FSIN (angle)
*TYPE FSIN(3.14159/4)
0.7071*

The format for calculation the sine of an angle in degrees is:
FSIN (degrees* 3.14159/180)
*TYPE FSIN<30*3.14159/180)
= 0.5000*

5.13.2

Cosine Function (FCOS)

The cosine function is used to calculate the cosine of a userspecified angle in radians.

The format for FCOS is:

FCOS (angle)

5-26

*TYPE FCOSC2*3.14159),!
1.0000
*TYPE FC~SC.50000),!
=
0.8776
*TYPE FCOSC45*3.14159/1R~}
0.7071*
---~

5.13.3

Exponential Function (FEXP)

The exponential function (FEXP) is used to compute e
to a power specified by the user.

(e=2.7l828)

The format for FEXP is:

FEXP (power)

*TYPE FEXP(l),,!

2.7183
*TYPE FEXP(0),!
=
1 .0000
*TYPE FEXPC-1-23456)
= 0.0000*

5.13.4

Logarithm Function (FLOG)

The logarithm function (FLOG) is used to compute the natural
logarithm (loge) of a number specified by the user.

The format for

FLOG is:
FLOG (number)
*TYPE FLOG<I.0000),!
0.0000
*TYPE FLOG(1.98765),!
=
0.6870
*TYPE FLOG(2.06S)
=
0.7251*

The following formulas are useful for finding logarithms to base
10:

5-27

5.13.5

Arctangent Function (FATN)

The arctangent function (FATN) is used to calculate the angle
in radians of a user-specified tangent.

The format for FATN is:

FATN (tangent)

*T'lPE FATNC1.) .. !
=
0.7854
*T'lPE FATNC.31305) .. !
=
0.3034
*TYPE FATNC3.14159)
=

1 .2626*

5.13.6

Square Root Function (FSQT)

The square root function (FSQT) is used to compute the square
root of an expression.

The format for FSQT is:

FSQT (expression)

*TYPE FSQT(4) .. !
=
2.0000
*T'lPE FSQT(9) .. !
= 3.0000
*SET Z=FSQT(144);TYPE Z
=
12.0000*

5.13.7

Absolute Value Function (FABS)

The absolute value function (FABS) is used to indicate the
absolute (positive) value of an expression.
FABS (expression)

5-28

The format for FABS is:

*TYPE FABS<-66)#!
= 66.0000
*TYPE FABS(+23)#!
23.0000
*TYPE FABS<-99.05)
99.0500*

=
=

5.13.8

Sign Part Function (FSGN)

The sign part function (FSGN) is used to output the sign part

(+ or -) of a number with a value of 1.

FSGN (0)=1.

The format for

FSGN is:
FSGN (expression)
*TYPE FSGNC6-4),!
=
1 .0000
*TYPE FSGN(0)#!
1.0000
*TYPE FSGNC-7)
1.0000*

=
=-

5.13.9

Integer Part Function (FITR)

The integer part function (FITR) is used to output the integer
part of a number.

The format for FITR is:

FITR (expression)
For positive numbers, FITR(X) is the greatest integer function.
For negative numbers, FITR(-X) is the integer part of

-x.

The

greatest integer function for negative numbers is obtained by FITR
(-X)-l.

For example:

*TYPE FITRC5.2),!
= 5.0000
*TYPE FITRC55.66),!
55.0000
*TYPE FITRC-4.1)
=- 4.0000*

5-29

5.13.10

Random Number Function (FRAN)

The random number function (FRAN) is used to generate nonstatistical pseudo-random numbers in the range 0.5000 to 0.9999.
No argument is used with the FRAN function.

The format for FRAN is:

FRAN ( )
*TYPE FRAN(),!
=
0.6073
*TYPE FRANC)
=
0.7376*

FRAN can be used to produce a less biased number.

For example:

*SET A=FRANC)*S0
*SET B=A-FITRCA)
The value assigned to B is a random number in the range 0.0000
to 0.9999.
5.14

FOCAL OUTPUT OPERATIONS
The following is a description of symbols used in FOCAL output

operations:
Symbol
To set output format,

To type symbol table,

EXElanation

TYPE %x.y

Where x is the total
number of digits, and y
is the number of digits
to the right of the
decimal point.

TYPE %6.3, 123.456

FOCAL prints: =+123.456

TYPE %

Resets output format to
floating point.

TYPE $

Other statements may not
follow on this line.

5-30

5.15

CONTROL CHARACTERS
FOCAL control characters and their explanations are shown below:
%

Output format delimiter
Carriage return and line feed

Carriage return

Type symbol table contents

(

Parentheses
Square brackets

I
"\

(mathematics)

Angle brackets

" "

Quotation marks

(text string)

Question marks

(trace feature)

SPACE key (names)
RETURN key (lines)

(nonprinting)

ALT MODE key (with ASK statement)
COMMA (expressions)

Semicolon (commands and statements)

5-31

TABLE 5-1
FOCAL COMMAND SUMMARY
Command

Abbreviation

Example of Form

Explanation

ASK

ASK X,Y,Z

FOCAL prints a colon· for each
variable; the user types a value
to define each variable.

COMMENT

If a line begins with the letter
C, the remainder of the line will
be ignored.

CONTINUE

C
D

C
DO 4.1

Dummy lines.

DO 4.0

Execute all group 4 lines; return
to command following DO command,
or when a RETURN is encountered.

DO ALL

Execute all program lines until a
RETURN is encountered.

ERASE

Erases the symbol table.

ERASE 2.0

Erases all group 2 lines.

ERASE 2.1

Erases line 2.1.

ERASE ALL

Erases all user input.

DO
L11
I

Execute line 4.1; return to command following DO command.

ERASE

FOR

FOR i=x,y,z;

(commands)

Where the command following is
executed at each new value.
x=initial value of i.
y=value added to i until i is
greater than z.
Starts indirect program at lowest
numbered line number.

Table 5-1.
Command

Abbreviation

(Cont.)

Example of Form

Explanation

GO?

S t,arts at lowes t numbe:red 1 i.ne
number and traces 'entire indirect
program un til another ?' is e~n
countered, or unt.il completi.on
of program.

GO TO

GOTO 3.4

St.arts indirect program (t,ransfers
control to line 3.4). Must have
argument.

IF (X)Ln,Ln,Ln
IF (X)Ln,Lni (commands)
IF (X)Lni (commands)

Where X is a defined identifier,
a value, or an expression, followed
by three line numbers.
If X is
less than zero, control is transferred to the first line n.umber.
If X is equal to zero, con.trol is
to the second line number.
If X
is greater than zero, control is
to the third 1 ina numbE~r.

LIBRl\RY CALL

LIBRARY CALL name

Calls stored program

LIBRARY SAVE

LIBRARY SAVE name

Saves program on the disk.

MODIFY

MODIFY n

Enables editing of any character
on line n.

QUIT

Returns control to the usero

RETURN

Terminates DO subroutines, l:'eturning to the original sequence.

SET

SET A=5/B*Ci

Defines identifiers in the symbol
table.

w
w

fl~om

the disk.

Table 5-1.
Conunand
TYPE

WRITE
111

I
W
~

Abbreviation

(Cont.)

Example of Form

Explanation

TYPE A+B-C;

Evaluates expression and prints =
and result in current output
format.

TYPE A-B,C/E;

Computes and prints each expression separated by conunas.

TYPE "TEXT STRING"

Print 9 .text. May be followed by
! to generate carriage returnline feed, or # to generate
carriage return.

WRITE

FOCAL prints the entire indirect
program.

WRITE ALL

WRITE 1.0

FOCAL prints all group 1 lines.

WRITE 1.1

FOCAL prints line 1.1.

TABLE 5-2
FOCAL FUNCTIONS
Function

Format

Square Root

FSQT(x)

Where x is a positive number or
expression greater than zero.

Absolute Value

FABS(x)

FOCAL ignores the sign of x.

Sign Part

FSGN(x)

FOCAL evaluates the sign part only,
with 1.0000 as integer.

Integer Part

FITR(x)

FOCAL operates on the integer part
of x, ignoring any fractional part.

Random Number
Generator

FRAN (x)

FOCAL generates a random number.
The value of x is ignored.

7Exponential

FEXP(x)

FOCAL generates e to the power x.
(2.71828 X )

7Sine

FSIN(x)

FOCAL generates the sine of x in
radians.

7Cosine

FCOS(x)

FOCAL generates the cosine of x in
radians.

7Arctangent

FATN(x)

FOCAL generates the arctangent of
x in radians.

7Logarithm

FLOG (x)

FOCAL generates loge (x) .

Interpretation

7These are extended functions and may be chosen or deleted when
FOCAL is loaded.

5-35

TABLE 5-3
FOCAL ERROR MESSAGES
Message
?OO.OO

?01.00
?01.40
?01.78
?01.96
?Ol. :5

?01.;4
?02.32
?02.52
?02.79
?03.05
?03.28
?04.39
?04.52
?04.60'
?04. :3
?05.48
?06.06
?06.54
?07.22
?07.38
?07.:9
?07.;6
?08.47
?09.11
? 10. : 5
?11.35
?20.34
?23.36

Explanation
Manual start given from console.
Interrupt from keyboard via CTRL/C.
Illegal step or line number used.
Group number is too large.
Double periods found in a line number.
Line number is too large.
Group zero is an illegal line number.
Nonexistent group referenced by DO.
Nonexistent line referenced by DO.
Storage was filled by push-down list.
Nonexistent line used after GOTO or IF.
Illegal command used.
Left of = in error in FOR or SET.
Excess right terminators encountered.
Illegal terminator in FOR command.
Missing argument in display command.
Bad argument to MODIFY.
Illegal use of function or number.
Storage is filled by variables.
Operator missing in expression or double E.
No operator used before parenthesis.
No argument given after function call.
Illegal function name or double operators.
Parentheses do not match.
Bad argument in ERASE.
Storage was filled by text.
Input buffer has overflowed.
Logarithm of zero requested.
Literal number is too large.

5-36

Table 5-3.

(Cont.)

Message

Explanation

?26.99

Exponent is too large or negative.

728,,73

Division by zero

?30.05

Imaginary square roots required.

?3l.<7

Illegal character, unavailable command, or unavailable
function used.

?30.7l

Undefined library command.

? 30.>0

Bad argument or missing argument to library command.

?3l.42

No such name in library directory.

?3l.43

Attempt to enter a duplicate name in the directory.

?3l.44

Library directory is full.

5-37

CP~PTER

FORTRAN

FORTRAN-D compiles and runs programs written in the PDP-8
version of FORTruL~ II8

Programs (usually created and stored with

the Symbolic Editor) are compiled in a single pass and executed
(automatically) immediately following compilation.
6.1

CALLING FORTRAN-D
To use FORTP~N-D, type:
.R FORT

FORTRAN requests the name of the input file, i.e., the file containing the FORTRAN program to be compiled and run.
with the file name and the RETURN key.

The user responds

FORTRAN then requests the

name of an output file in which to store the compiled version of the
program.

For normal usage, just the RETURN key need be typed.

FORTRAN places the compiled code in a file of its own, then proceeds
to run the program.
If a file name is entered for output, FORTRAN creates a permanent file in which the compiled binary program is saved.
possible to rerun this program without recompiling it.

It is then
To run an

already compiled program, call the FORTRAN operating system directly
by typing:

.R FOSL
FOSL requests the name of an input file.
file containing the compiled binary.

6-1

Enter the name of the

For example, if the user types:

.R FORT
INPUT:MATRIX
OUTPUT:
FORTRAN compiles and executes the program MATRIX but does not save
the compiled binary.
FORTRAN compiles and executes the program MATRIX and then leaves
the compiled binary in the file named BMTRIX when the user types:
.R FORT
INPUT:MATRIX
OUTPUTIBMTRIX
The FORTRAN binary program BMTRIX is executed without first
being compiled when the user types:
.R FOSL
INPUT:BMTRIX
All FORTRAN programs return to the Monitor when they have completed execution.
6.2

USING FORTRAN-D
Differing versions of PDP-8 FORTRAN offer slightly different

features.

FORTRAN-D differs in the way it is called into use

(described above), and in its I/O capability (described below).
FORTRAN-D allows three data formats:
I

Integer format

Exponential format

Alpha format, ASCII value of a character is stored as an
integer value.

6-2

The standard device for READ and WRITE statements is the terminal,

which is assigned device code 1.

Because the terminal is so

frequently used, FORTRAN-D includes two special input/output instructions, ACCEPT and TYPE.

nali

These instructions imply use of the termi-

therefore, the device code need not be specified.

ACCEPT is

especially convenient if data is to be entered at the keyboard
because this instruction automatically supplies a line feed when the
RETURN key is typed.

Also, the user can correct an erroneously

typed value by striking the RUBOUT key.
A FORTRAN-D program can also utilize the high-speed r,eader and
punch for I/O.

These devices are assigned code 2.

Because the high-

speed reader and punch are shared by all users, it is necessary to
assign them if they are to be used.

Assign the appropriate devices

and mount tapes in the reader before running FORTRAN-D.

An auto-

matic DEASSIGN is performed by FORTRAN before it returns to the
Monitor; therefore, the user must reassign the devices before each
run.
FORTRAN-D also allows programs to read and write data files on
the disk.
files.

These data files are completely separate from the program

Data files are read and written by standard READ and WRITE

statements within the FORTRAN~D program.
disk is 3.

The device code for the

Because programs using the disk are treated differently

by FORT (the FORTRAN-D compiler), it is necessary to identify programs which use the disk.

These programs are identified by a DEFINE

DISK statement as the first statement in any such FORTRAN-D program
including a READ or WRITE statement with device code 3.
Just as FORT itself must ask for the name of its input and
output files, so must a FORTRAN program ask for the names of its disk
files.

FORTRAN-D programs do this by typing INPUT: and OUTPUT: a

second time.

The user responds by typing the name of the files to be

read or written by the program.

FORTRAN-D asks for both input and

output for all programs which include a DEFINE DISK statement.

6-3

only input {or output} is to be used, the user responds to the other
by typing the RETURN key.
6.3

LINE FORMAT
FORTRAN programs consist of a series of lines, each a string

of 72 characters or less (the width of the terminal paper from
margin to margin).

Each line contains two fields:

the first, which

begins at the left margin, is an identification field: the second
contains the statement field.

Termination of a line is indicated to

the computer by a carriage return, accomplished by typing the RETURN
key.
The identification field can be blank, or can contain one of the
following types of identification:
1.

A statement number. This number, which can be any positive
integer from 1 to 2047 inclusive, identifies the statement
on that line for reference by other parts of the program.
Statement numbers are used for program control or to assist
the programmer in identifying segments of his program.

The letter, C.
as a comment.

This identifies the remainder of the line

Although the identification field may be left blank, it cannot
be omitted entirely.

The statement field begins immediately after

a blank space and extends through the next carriage return.
FORTRAN program is shown below:
C
5

30
32
33

THIS PROGRAM CALCULATES FACTORIALS
TYPE 200
ACCEPT 300,N
IFACT=1
IF (N-I) 5,32,33
TYPE 400,N,IFACT
GO TO 10
DO 35 I=l,N
IFACT=IFACT*I

6-4

A sample

CONTINUE
GO TO 32
FORMAT (/ .. "PLEASE TYPE A POSITIVE NUMBER .... /)
FORMAT (i)
FORMAT (; .. l/n FACTORIAL 15" .. 1)

200
300
400

END

FORTRAN source programs are generated using the Symbolic Editor
Program.

The Editor will facilitate formatting lines by use of a

tab character, permitting automatic movement to an indented second
field.
6.3.1

Statement Numbers
Each statement can have a positive, nonzero integer (0-2047) as

its number.

The statement number is used to reference that parti-

cular statement elsewhere in a program.

A statement number consists

of one to four digits beginning at the left hand margin and is
followed by a space or tab.

Statement numbers can be assigned non-

sequentially; however, no two statements can have the same number.
There must be no more than 40 statement numbers in a given program,
and they must have a value of 2047
6.3.2

(decimal) or less.

Statement Continuation Character
Frequently, a statement is too long to fit on one line.

If the

character single quote (I) appears as the last character of a line
before the carriage return, the next line is treated as a continuation of the preceding statement.

A statement may be continued on as

many lines as necessary to complete it, but the maximum number of
characters in the statement cannot exceed 128 (about two formatted
lines).
10

For example:
A=B**2-C4.*A*C/CB**2+1.S*A*C»*4.3'
+B**2+(CSQTFCC)*SQTFCD»/CB**2+1.S*A*C»

is equivalent to the formula:

6-5

Although the continuation character,

(I)

allows a single

statement to extend over two or more lines, no more than one statement can be written on one line.
6.4

FORTRAN STATEMENTS
FORTRAN statements are of several types with various functions

distinguished as follows:
1.

comment statements allow a programmer to insert notes
within the program.

Arithmetic statements resemble algebraic formulas.
define calculations to be performed.

Control statements govern the sequence of statement
execution within a program. These statements reference
program line numbers.

Specification statements allocate data storage and specify
input/output formats.

Input/output statements control the transfer of information
into and out of the computer.

6.4.1

They

Comment Statements
The character C, at the left margin of a line, designates that

line as a comment line.

A comment has no effect upon the compilation

process but can serve as a guide to program logic for later debugging,
etc.

There is no limit to the number of comment lines which can

appear in a given program.

A comment cannot be continued by use of

the continuation character,

(I), but must be continued in a second

comment statement.
C
C

For example:

THIS IS AN EXAMPLE

OF A COMMENT

6-6

6.4.2

Character Set
The following characters are used in the FORTRAN language:
1.

The alphabetic characters, A through Z.

The numeric characters, 0 through 9.

The control characters:
semicolon

CR carriage return
LF line feed

. period
, single quote

left parenthesis

" double quote

right parenthesis

, conuna
4.

The operators:

** exponentiation

/ division

+ addition

* multiplication

- subtraction

= replacement

All other characters are ignored by the Compiler except as
Hollerith information found in FORMAT statements (where all terminal
characters are legal).

The SPACE character has no granunatical func-

tion (it is not a delimiter) except in FORMAT statements and can be
used freely to make a program easier to read.
6.4.3

Constants
Constants are explicit numeric values appearing in statements.

Two types of constants, integer and real, are permitted in FORTRAN.
6.4.3.1

Integer Constants -- Integer (fixed-point) constants are

represented by a string of one to four decimal digits, written with
an optional sign and without a decimal point.
must fall within the range +2047.

6-7

For example:

An integer constant

47
+47
-2
0434
-0
6.4.3.2

(+ sign is optional)
(leading zeros are ignored)
(same as zero)

Real Constants -- Real constants are represented by a digit

string, an explicit decimal point, and are written with an optional
l
sign.
Real constants can also be written in exponential notation
3
with an integer exponent to denote a power of ten (i.e., 7.2 x 10

is written 7.2E+3). A real constant may consist of any number of
digits but only the leftmost six digits appear in the compiled program.

Real constants must fall within the range 0.14 x 1038
1.7 x 10
. For example:

+4.50
(plus sign is optional)
4.50
-23.09
14
-3.0E14(same as -3.0 x 10 )
7.
(saved as 7.00000, not the same as the integer 7)
6.4.3.3

Fixed and Floating-Point Representation -- The difference

between integers and real numbers in FORTRAN is the way in which
each is represented in core memory.

Both types of numbers are con-

verted to binary to be stored in the computer.
A FORTRAN integer is stored in one l2-bit computer word.

The

sign of the number is kept in the high-order bit and the magnitude
(the integer value) in the remaining 11 bits.

This representation,

shown schematically in Figure 6-1, is called fixed point, because the
decimal point is always considered to be to the right of the rightmost digit.

A FORTRAN integer may not exceed the range of

~2047.

All integers greater than +2047 are taken modulo 2048 (i.e., 2049 is
considered to be I i 4099, to be 3).

lWhere a number is to be identified as being negative, a minus sign
(-) must be used. A plus sign (+) is optional; with no sign, a
number is considered positive.

6-8

The floating-point format consists of two parts:
(or characieristic) and a mantissa~

an exponent

The mantissa is a binary frac-

tion with the radix point assumed to be to the left of bit one of
the mantissa.

The mantissa is always normalized; meaning it is

stored with leading zeros eliminated so that the leftmost bit is
always significant.

The exponent represents the power of two by

which the mantissa is multiplied to obtain the true value of the
number for use in computation.

The exponent and mantissa are both

stored in two's complement form.
SIGN

+
MAGNITUDE

FORTRAN INTEGER

SIGN OF EXPONENT

~
EXPONENT
11
SIGN OF
0
MANTlssA ............
"r----;-_ _ _ _ _ _ _ _ _ _ _ _ _ _--.

~I~~
o

_____

M_A_NT_IS_SA
_______

~
11

~I__________

M_A_NT_IS_SA
_________

b. FLOATING POINT

Figure 6-1.

Number Representation

Users should not attempt to input floating point constants of
more than six decimal digits, either in the FORTRAN source program
or via the run-time ACCEPT statement.
Integers cannot appear in floating-point expressions except as
exponent or subscripts.

Some examples of illegal and legal expres-

sions are as follows:

6-9

Expression

Legal

Mode

A(I)*B(J)**2

Yes

Floating

I(M)*K(N)

Yes

Fixed

16. *B

Yes

Floating

(K+16)*3

Yes

Fixed

A**(1+2)/B

Yes

Floating

8*A

4.*J

I+D

6.4.4

Variables
A variable is a symbol whose value may change during execution

of a program.

The name of a variable consists of one or more alpha-

numeric characters, the first of which must be alphabetic.

Only the

first four characters are interpreted as defining the variable name;
the rest are ignored.

For example, the name EPSILON would be inter-

preted by the Compiler as EPSI.

Since only the first four characters

are meaningful, the two names XSUMI and XSUM2 would be considered
identical.
Spaces, as mentioned earlier, are ignored.
represents one variable, not two.

The name EX IT

Thus, EX IT, EXIT, or even EXI T

are identical names as far as the Compiler is concerned, and they
all refer to the same numerical quantity.
The type (or mode) of a variable (integer or real) is determined
by the first letter of the variable name.
1.

Integer variables begin with the letters:
I, J, K, L, M, or N

Real variables begin with any letter other than those above.

6-10

Variables of each type may be either scalar or array variables,
as explained below.
6.4.4.1 Integer Variables -- Integer variables undergo arithmetic
calculations with automatic truncation of any fractional part. For
example, if the current value of K is 5 and the current value of J
is 9, then J/K would yield 1 as a result.
6.4.4.2 Real Variables -- A variable is real when its name begins
with any character other than I, J, K, L, M, or N. Real variables
undergo no truncation in arithmetic calculations. Real variables
may be converted to integer variables, and vice-versa, across an
equal sign.
6.4.4.3

Scalar Variables -- A scalar variable, which may be either

integer or real, represents a single number, as opposed to an array
(below) representing a collection of numbers. For example, the
following are scalar variables:
LM
G2

A
TOTAL

(considered to be TOTA by the computer)

6.4.4.4 Array Variables -- An array variable represents a single
element of a one-dimensional array of quantities. The variable is
denoted by the array name followed by a subscript enclosed in parentheses. The subscript may be any combination of integer variables
and integer constants forming a valid expression, as follows:
(V)

(V+C)

(V-C)

(C)

where V is a fixed po~nt (integer) variable, and C is a fixed-point
constant (not equal to 0).

6-11

The value of the expression in parentheses determines the
referenced array element. For example, th~ row matrix, AI' would
be represented by the subscripted variable A{l), and the second
element in the row would be represented by A(2). Examples of array
variables are:
Legal Forms
Y(l)
A(K+2)
6.4.5

Illegal Forms
A(2+l)
B{C)

DIMENSION Statement

Array names must be identified as such to the FORTRAN Compiler.
Two items of information must be provided in any program using arrays:
1.
2.

Which are the subscripted variables?
What is the maximum value of the subscript? (When an
array is used, a certain amount of storage space must be
set aside by the Compiler for the array elements.)

This information is provided by the DIMENSION statement:
DIMENSION A(20)~B(15)

where A and B are array names, and the integer constants 20 and 15
are the maximum dimensions of each subscript.
The rules governing the use of array variables and the DIMENSION
statement are as follows:
1.
2.

All array names must appear in a DIMENSION statement.
DIMENSION statements may be used more than once and may
appear anywhere in the FORTRAN program, provided that the
DIMENSION of an array appears before any statement which
references the array.
Any number of arrays can be defined in a single DIMENSION
statement.

6-12

For notes on how to implement double subscripts (i.e.,
A{'I,J», see Section 6.8, Implementation Notes.

Array variables may be either integer or real, depending upon
the initial letter of the array name.
DIMENSION LIST(30)#MATC100),REGRC20)
In the statement above, the names LIST and MAT designate integer
arrays; that is, all elements of both arrays are integers.
name, REGR, designates a floating point, or real array.

The third

The first

array is a list containing a maximum of 30 elements; the second array
has a maximum of 100 elements.
The third array is a floating-point array and there are a maximum of 20 elements in it.

Not all elements of an array need be used

in the course of a program; but, if using the DIMENSION statement
the variable LIST {3l}

could not be referenced without the occur-

rence of an error message.
6.5

FORTRAN ARITHMETIC

6.5.1

Arithmetic Operators
The arithmetic operators are symbols representing the common

arithmetic operations.

The important rule about operators in the

FORTRAN arithmetic expressions is that:

every operation must be

explicitly represented by an operator.

In particular, the multipli-

cation sign must never be omitted.

A symbol for exponentiation is

also provided since superscript notation is not available on a
terminal.
Normally, a FORTRAN expression is evaluated from left to right,
like an algebraic formula.

There are exceptions to this rule; cer-

tain operations are always performed before others, regardless of
order.

This priority of evaluation is as follows:

6-13

Expressions within parentheses

2•

Unary minus

Exponentiation

Multiplication or Division

* or /

Addition or Subtraction

+ or -

The term "binding strength" is frequently used to refer to the
relative position of an operator in a table such as the one above,
which is in order of descending binding strength.

Thus, exponentia-

tion has a greater binding strength than addition, and multiplication
and division have equal binding strength.
The unary minus is the arithmetic operator which indicates that
a quantity is less than zero, such as -53, -K, -12.3.

It refers

only to the constant or variable which it precedes as opposed to a
binary operator, which refers to operands on either side of itself
as in the expression A-B.

A unary minus is recognized by the fact

that it is preceded by another operator, not by an operand.

For

example:

A+S**-2/C-D
The first minus sign (indicating a negative exponent) is unary;
the second (indicating subtraction) is binary.

At present it is not

possible to raise an integer variable or integer constant to an
integer value with FORTRAN-D.

Only real values can be raised to

integer powers.
The left-to-right rule can be stated more precisely:

A sequence

of operations of equal binding strength is evaluated from left to
right.

To change the order of evaluation, parentheses are required.

Thus, the expression A-B*C is evaluated as A-(B*C), not {A-B)*C.
Examples of the left-to-right rule follow:

6-14

The expression:

6.5.1.1

Is evaluated as:

A/B*C

(A/B) *C

A/B/A

(A/B) /e

A**B**C

(A**B) **C

Use of Parentheses -- Note the use of parentheses in the

example below.

They are used to enclose the subscript of the dimen-

sienal variable, Di to specify the order of operations of the expression involving A, B, and Ci and to enclose the argument of the
function SINF.
DCI)+CA+B) •• C+SINFCX)

In algebra there are several devices, such as square brackets
[ ], rococo brackets {} , etc., for distinguishing between levels
when expressions are nested.

In FORTRAN, only the parentheses are

available, so the programmer must be especially careful to pair
parentheses properly.

In any given expression, the number of left

parentheses must be equal to the number of right parentheses.
An easy way to check the proper pairing of parentheses is by
counting out, illustrated in the following example:

(Z+AM* (AM+l.»)/«(X**2+C**2)*P)
1
2
10 12
1 0
The procedure is this:

Reading the expression from left to

right, assign the number, 1, to the first left parenthesis (if you
encounter a right parenthesis first, the expression is already
wrong).

Increase the count by one each time a left parenthesis is

read, and decrease the count by one when a right parenthesis is
found.

When the expression has been completely scanned, the count

should be zero.

If it becomes less than zero during the scanning,

there are too many right parentheses.

If it is greater than zero at

the end of an expression, there are excess left parentheses.

6-15

6.5.2

Arithmetic Expressions
An algebraic formula such as:

represents a relationship between symbols (a, b, x, xO) and constants
(5, 4, 2) indicated by mathematical functions and arithmetic
operators (+, -, multiplication, exponentiation).

This same formula

can be written as a FORTRAN arithmetic expression with very little
change in appearance:

The construction of both expressions is the same; the differences
are notational.
Elements of an arithmetic expression are of four types:
stants, variables, operators, and functions.

con-

An expression may

consist of a single constant or variable or a string of constants,
variables, and functions connected by operators.
Examples of arithmetic expressions follow; each expression is
shown with its corresponding algebraic form.
Algebraic Expression

FORTRAN Expression

2Vx

2.*SQTF(X}/3.

3X7T -

2 (x+y)

(3.*X*PI-2.*

4.25
aOsin 9 + 2a cos(9 - 45)

6-16

(X+Y)

) /4.25

A*SINF(THTA)+2.*A*COSF
( (THTA)-O.78540)

(A**2-B**2) /

6.5.3

(A+B)**2

Arithmetic Statements

The arithmetic statement relates a variable, V, to an arithmetic
expression, E, by means of the replacement operator, (+):
V=E
Such a statement looks like a mathematical equation, but is treated
differently. The equal sign is interpreted in a special sensei it
does not represent a relationship between left and right members,
but rather specifies an operation to be performed.
In an arithmetic statement, the value of the expression to the
right of the equal sign replaces the value of the variable on the
left. This means that the value of the left-hand variable will
change after the execution of an arithmetic statement. A few
illustrations of arithmetic statements are given below.

+ AXT
T = 2.*PI*SQTF{1./G)

3.
4.
5.

PI = 3.14159
THTA = OMGA + ALPH*T**2/2.
MIN = MINO

INDX = INDX + 2

VMAX = VO

With the interpretation of the equal sign stated above, Example
6 becomes meaningful as an arithmetic statement. If, for example,
the value of INDX is 40 before the statement is executed, its value
will be 42 after execution.

6-17

In arithmetic expressions, a binary operator requires an operand
on its left and right. The equal sign of an arithmetic statement is
also considered to be.a binary operator, as demonstrated in the
following revised table of operators:
Operator

Use

- (Unary)
*

-A
A**B
A*B

AlB

A+B
A-B

(Binary)

A=B

Interpretation
negate A
raise A to the Bth power
multiply A by B
divide A by B
add B to A
subtract B from A
replace the value of A with the
value of B

The replacement operator is considered to have the lowest
binding strength of all operators; therefore, the expression on the
right is evaluated before the operation indicated by the equal sign
is performed.
6.5.3.1

Multiple Replacement -- An important result of treating the

equal sign as an operator is that operations can be performed in
sequence. Just as there can be a series of additions, A+B+C, there
can also be a series of replacements:
A=B=C=D
Notice that because the operand to the left of an equal sign
must be a variable, only the rightmost operand, represented by D in
the example, may be an arithmetic expression. The statement is interpreted as follows:
"Let the value of the expression D replace the
value of the variable C, which then replaces the value of the
variable B" and so on. In other words, the value of the rightmost
expression is given to each of the variables in the string to the
left. A common use for this construction is in setting up initial
values:
6-18

XZRO=SZRO=AZRO=0.
T=Ti=T2*T3-60.
P-FP 5 4.*ATMoAK

Only simple variables will compile correctly in this manner.
For example, 'statements of the type A(1)=A(2)=R(1)=0.123 are not
allowed and will not compile properly (subscripted variables may
not be used in multiple replacement statements).
Multiple replacement done in a single statement must not contain
mixed mode variables. That is;
A=B=C=10.

compiles correctly
compiles correctly
does not compile correctly

I=J=7
A=J=7
Mode Conversion

Another useful result in treating the equal sign as an operator
is that the value of an expression on the right of an equal sign is
converted to the mode of the left-hand variable, if necessary, before
storage. For example:
A=M

Stores the value of M as a floating-point number in A

K=B

Stores the value of B (truncated) as an integer number
in K

If B = 4.75 and M = 7, the conversion above will result in the
following values being assigned:
A = 7.00000
K = 4

6-19

6.5.4

Functions
Functions are used in FORTRAN just as they are in ordinary

mathematics, acting as variables in arithmetic expressions.

The

function name represents a call to a special subprogram which performs the calculations to evaluate the function: the result is used
in the computation of the expression in which the function occurs.
FORTRAN-D provides several mathematical functions:

square root,

sine, cosine, arctangent, exponentiation, and natural logarithm.
The argument of a function can be a simple variable, a subscripted variable, or an expression.
floating-point format.

The argument must be in a

FORTRAN recognizes a symbol as a function

when it is a predefined symbol ending in F and followed by an
argument enclosed in parentheses (if the F is missing from the
term, the symbol is treated as a subscripted variable).

The argu-

ment of a function can consist of another function or groups of
functions.

For example, the expression:

LOGFCSINFCX/2.)/COSFCX/2.»
is equivalent to log

tan

(~)

FORTRAN-D contains the following functions:
Meaning

Function Name

ATNF(X)

Arctangent X, where X is expressed
in radians

COSF(X)

Cosine of X, where X is expressed
in radians

EXPF(X)

Exponential of X

LOGF(X)

Logarithm of X

SINF(X)

Sine of X, where X is expressed
in radians

SQTF(X)

Square root of

6-20

6.6

PROGRAM CONTROL STATEMENTS
In this section, FORTRAN statements are discussed in the con-

text of program sequences.

FORTRAN statements are executed in the

order in which they are written unless instructions are given to the
contrary by use of the program control statements.

These statements

allow the programmer to alter sequence, repeat sections, suspend
operations, or bring the program to a complete halt.

6.6.1

END Statement
END occurs alone on a line and indicates the physical end of

the program to the FORTRAN Compiler.
number.

6.6.2

It can be preceded by a line

Every program must contain an END statement.
STOP Statement

A program arranged so that the last written statement is the
final and only stopping place needs no other terminating indication;
the END statement automatically determines the final halt.

Many

programs, however, contain loops and branches so that the last
executed statement can be somewhere in the middle of the written
program.

Frequently there is more than one stopping point.

terminations are indicated by the STOP statement.

Such

This causes a

final, complete halt; no further computation is possible, although
the program may be completely restarted from the beginning.
When a STOP is encountered during program execution, the
system signifies that a STOP has occurred by outputting an exclamation point (1) to the terminal or high-speed punch, whichever is
being used as the output device.

6-21

6.6.3

PAUSE Statement
The STOP statement prevents further computation after it has

been executed.

There is a way, however, to suspend operation for a

time and then restart the program.

This procedure is frequently

necessary when the user must do such tasks as loading and unloading
paper tapes in the middle of a program.
is provided by the PAUSE statement.

This kind of temporary halt

The PAUSE statement halts the

program and returns control to the EduSystem 50 Monitor.

The user

may then perform any necessary manipulations and restart the program
by typing the Monitor command START.
6.6.4

GO TO Statement
There are various ways in which program flow may be directed.

As shown schematically in Figure 6-2, a program may be a straightline sequence (1), or it may branch to an entirely different sequence (2), return to an earlier point (3), or skip to a later point
(4).

The blocks represent sections of FORTRAN code.

The lines

indicate the path which control takes as the program executes.
All of these branches can be performed in several ways, the
simplest of which uses the statement:

Figure 6-2.

Program Flow

6-22

GO TO n

where n is a statement number in the program. The use of this
statement is described in the following example, which also illustrates the construction of a loop, the name given to program branches
of the type shown in the example above.
6.6.5

Example of Integer Summation

In the following example, the sum of successive integers is
accumulated by repeated addition. The main computation i.s provided
by the three-instruction loop beginning with Statement 2. The
statements preceding this loop provide the starting conditions, called
the initialization. The partial sum is set to zero, and the first
integer is given the value of one. The loop then adds the integer
value to the partial sum, increments the integer, and repeats the
operation.
C

SUM OF FIRST N INTEGERS BY ITERATION
KSUM=0
iNUM=l

KSUM=INUM+KSUM
INUM=INUM+l

GO TO 2
END

6.6.6

IF Statement
The program shown in the preceding example performs the required

computation, but note that the loop is endless. To get out of the
loop the user must know when to stop the iteration and what to do
afterwards.
The IF statement fills both requirements.
form:
IF(E) K,L,M

6-23

It has the following

where E is any variable name, arithmetic expression, or arithmetic
statement, 'and K, L, and M are statement numbers. The statement
is interpreted in this way:
If the value of E < O,GO TO statement K
E = O,GO TO statement L
E > O,GO TO statement M
Thus, the IF statement decides when to stop a loop by evaluating
an expression. It also provides program branch choices with the
transfer of control, depending on the results of the evaluation of
E.

For example:

c
2

SUM OF THE FIRST 50 INTEGERS
KSUM=0
IOOM=l
KSUM=INUM+KSUM
INUM=INUM+l
IF CINUM-50)2,2,3
STOP
END
In the foregoing example, the initialization and main loop are

the same as for the example in Figure 6-2 except that the GO TO
statement of the earlier program has been replaced by an IF statement.

The IF statement says, "if the value of the variable INUM is

less than, or equal to, 50 (which is the same as saying that if the
value of the expression INUM-50 is less than or equal to zero),
transfer control to Statement 2 and continue the computation.
the value is greater than 50, stop."

(See Section 6.8, Implementa-

tion Notes, for an alternate solution.)
A loop may also be used to compute a series of values.

The

following illustration is an example of a program to generate terms
in the Fibonacci series of integers, in which each succeeding member of the series is the sum of the two members preceding it:

6-24

FIBONACCI SERIES. 100 TERMS
DIMENSION FIB(100)
FIBCl):l.e
FIB(2):1.e
K=3

~IKB(~)=FIBCK.l)+FIB(K-2)

STOP
END

IF (K-100)515110

In this program, the initialization includes a DIMENSION statement which reserves space in storage, and two statements which provide the starting values necessary to generate the series~ Each
time a term is computed, the subscript is incremented so that each
succeeding term is stored in the next location of the table. As
soon as the subscript is greater than 100, the calculation stops.
6.6.7

DO Loops
Iterative procedures such as the program loop are so common

that a more concise way of presenting them is warranted. Three
statements are required to initialize the subscript, increment it,
and test for termination. The following type of statement combines
all these functions:
DO n J=Kl,K2,K3
here n is a statement number,J is a simple (non-subscripted)
integer variable, and Kl, K2, and K3 are simple integer variables
or integer constants which provide, in order, the initial value to
which J is set, the maximum value of J for which the loop will. be
executed, and the amount by which J is incremented at each return
to the beginning of the loop. If K3 is omitted from the statement
it is assumed to be one (1). Statement n must be a CONTINUE
statement.

6-25

FIBONACCI SERIES. 100 TERMS
DIMENSION FIB(100)
FIBCl)=1.0
FIB(2)=1.0
DO 5 K=3. 100
FIBCK)=FIBCK-l)+FIBCK-2)
CONTINUE
STOP
END

In words, the DO statement says "Execute all statements through
Statement 5 with K=3; when Statement 5 is encountered, perform the
following test:

If K+l is less than or equal to 100, set K=K+l and

continue the program by executing the first statement after the DO
statement.

If K+l is greater than 100, the next sequential state-

ment following Statement 5 is executed."
DO loops are commonly used in computations with subscripted
variables.

In such cases, it is usually necessary to perform the

loops within loops.

Such nesting of DO loops is permitted in

FORTRAN.

C
5
C

FIRST LOOP
DO 10 1=1,20
X(I)=0.
NESTED LOOP FOLLOWS
DO 5 K=2,40,2
X(I)=X(I)+CBCK)-ZCK»**2
CONTINUE
END OF NESTED LOOP
ACI)=X(I)**2+CCI)
CONTI NUE

Sequential elements in the array X(I) are formed by summing
the square of the difference of every second element in the Band
Z arrays.

Then the array A(I)

is formed by summing every element

in the array C(I) and the square of every element in the array X(I).
The algebraic expression for the loop is as follows:

6-26

A.=x. 2
~

where

for i=1,2,3, ... 20

for k=2,4,6, ... 40

The following three rules

loops must be observed:

DO loops may be nested, but they may not overlap. Nested
loops may end on the same statement, but an inner loop may
not extend beyond the last statement of an outer loop.
Figure 6-3 schematically illustrates permitted and forbidden arrangements.

If the user transfers into the range of a DO loop, the
value to be incremented (J, for example) is not automatically initialized as specified in the DO statement.
Transferring into the range of a DO loop is allowed as
long as:

Control was originally transferred out of the DO loop
by some means other than by completing it.

Incrementing and testing start with the current value
of J at the time control returns to the loop.

A DO loop must end on a CONTINUE statement.

DOCE

DO
DO
DO
CONTiNUE
CONTiNUE
DO
DO
DO
CONTINUE
CONTINUE

CONTINUE
CONTiNUE
ILLEGAL NESTING
TECHNIQUES

lli
LEGAL NESTING
TECHNIQUES

Figure 6-3.

Legal and Illegal Nesting Techniques

6-27

DO
DO

CONTiNUE
DO

CONTINUE
CONTiNUE

CONTiNUE

6.6.7.1

[

CONTiNUE

CONTINUE

ACCEPTABLE
BRANCHING

Figure 6-4.

cP0

ILLEGAL
BRANCHING

Program Branching in DO Loops

CONTINUE Statement -- A special statement (CONTINUE) is

provided which is not an executable statement itself, but provides
a termination for all DO loops.
CONTINUE statement.

DO loops must be terminated on a

The CONTINUE statement is identified with the

line number given in the DO statement.

37
42

For example:

DO 37 MM=1,10
IF (X(MM)-100.) 37,42,31
CONTINUE
GO TO 102
STOP

A single CONTINUE statement can be referenced more than once

in a single DO loop or can serve as the terminating line for two or
more nested DO loops.
6.6.8

Computed GO TO
The GO TO statement previously described is unconditional and

provides no alternatives.
three branch points.

The IF statement offers a maximum of

One way of providing a greater number of alter-

natives is by using the computed GO TO, which has the following form:
GO TO (Kl,K2,K3, ... ,Kn),J

6-28

where Kn is~statement number, and J is a simple integer variable,
which takes on values of 1,2,3, ... n according to the results of
some previous computation.

For example:

IVAR=14*J/2+K
GO TO (S,7,S,7,S,7,10),IVAR
causes a branch to Statement 5 when IVAR=l, 3, or 5; to Statement
7 when IVAR=2, 4, or 6; and to Statement 10 when IVAR=7.

When IVAR

is less than 1 or greater than 7, the next sequential statement
after the GO TO is executed.
6.7

FORTRAN INPUT/OUTPUT
So far, we have assumed that all information (programs, data,

and sub-programs) is in memory, without regard to how it is put
there.

Programs are read by a special loader, but the programmer

is responsible for the input of data and the output of results by
including directions for I/O operations in his program.
For any input/output procedure, several questions must be
answered:
1.

In which direction is the data going? The data coming in
is being read into memory; information going out is being
written on whatever medium is specified.

Which device is being used? Information may be transferred between core and whatever input/output devices
are available; each I/O operation must specify the device
involved.

Where in core memory is the data coming from or going to?
The amount of data and its location in the computer storage
must be specified.

In what mode is the data represented? In addition to
floating and fixed-point modes for numeric data, there is
the Hollerith mode for transferring alphanumeric or text
information.

What is the arrangement of the data? The format of incoming or outgoing data must be specified.

For every data transfer between core memory and an external
device, two statements are required to provide all of the information listed above.

The first three items are specified by the

input/output statement, and the last two items are determined by
the FORMAT statement.
6.7.1

Data Formats
FORTRAN-D provides for communication of data to and from a

program in the following ways:
6.7.1.1

ASCII Coded Data -- The terminal can be used to transfer

data to the program either via the keyboard (in which case the user
types the data) or from previously punched paper tape (read via the
terminal tape reader).
terminal

Data can be output from a program to the

producing a printed copy with or without the corresponding

punched paper tape.

The high-speed reader and punch can also be

used for data transfer via punched paper tape.

No printed copy is

made when output is to the high-speed punch.
6.7.1.2

Binary Coded Data -- System disk can also be used for data

transfer, in which case the data is stored as a core image.

Integers

are read and written as single l2-bit words, floating-point numbers
as three words.

Alphanumeric information is transmitted as 8-bit

ASCII coded characters right-justified in l2-bit words (one character per word).
6.7.2

Input/Output Statements
Input/Output statements control the transfer of information.

As illustrated below, I/O statements consist of three basic items
of information:

the device being accessed and the direction of

transfer, the number of the FORMAT statement controlling the arrangement of data, and the list of variable names whose values are to be
output or changed by new input.

6-30

NOTE
There is a restriction on subscripted
variables when used with I/O statements.
Subscripts to be used with I/O statements must be of the form:
LL: where
each L is a letter, and not of the form
LD, where D is a digit. For example:
DO 10 Ll=1 .. 4
ACCEPT 7 .. ACL1)

will not store information correctly.
The statement should read:
DO 10 LL=1 .. 4
ACCEPT 1 .. ACLL)

ACCEPT N,V(l) ,V(I+l),V(I+2)

~
Llst of varlable names
Statement number of FORMAT
Statement
Device Selection and direction of
transfer
6.7.2.1

ACCEPT and TYPE Statements -- ACCEPT and TYPE transfer in-

formation between the terminal and EduSystem 50.

ACCEPT causes

information to be read into core memory from either the keyboard,
the terminal paper tape reader, or the high-speed reader if it is
assigned before calling FORTRAN-D.

ACCEPT is especially convenient

if data is to be entered at the keyboard since it automatically
supplies line feed when the RETURN key is typed.

Also, the user

may correct an erroneously typed value by typing the RUBOUT key.
TYPE causes information to be transferred from core memory
to the terminal printer, the terminal paper tape punch, or the
high-speed punch if it is assigned before calling FORTRAN-D.

6-31

If the- user needs the high-speed reader and punch for I/O, he
must assign the devices for his use before calling the FORTRAN
compiler (FORT) or operating system (FOSL).

Once logged into

EduSystem 50, he replies to Monitor's dot with the appropriate assign
statements.

For example:

.ASSIGN P

P ASSIGNED
.ASSIGN R
R ASSIGNED
The Monitor replies with P ASSIGNED and R ASSIGNED in response
to the user.

If the device requested is not available (being used

by someone else), the Monitor responds with a message telling who
has the device assigned.
code 2.

The high-speed reader/punch is device

If running several programs, the user should reassign the

devices before each run.

6.7.2.2

READ and WRITE Statements -- EduSystem 50 FORTRAN also

allows programs to read and write data files on disk.
files are completely separate from program files.

These data

Data files are

read and written by standard READ and WRITE statements within the
FORTRAN program.

The device code for the disk is 3.

Since pro-

grams which use disk are treated differently by FORT from those
which do not use disk, it is necessary to identify programs which
do.

This is done by placing a DEFINE DISK statement as the first

statement in any FORTRAN program which includes a READ or WRITE
statement with a device code of 3.
Just as FORT must ask for the names of its input and output
files, so must a FORTRAN program ask for the names of its disk
files.

FORTRAN programs do this by typing INPUT: and OUTPUT: a

second time.

The user responds by typing the names of the data

files to be read or written by the program.

6-32

FORTRAN will ask for

both INPUT and OUTPUT for all programs which include a DEFINE DISK
statement.

If only one is to be used, respond to the other by

typing the RETURN key;
6.7.3

Variable Specification in I/O Statements
Following the instruction that selects the device and direction

of transfer is the statement number of the FORMAT statement that
controls the arrangement of the information being transferred.

For

example:
ACCEPT 10#A
FORMAT <E)

Every I/O statement must have a reference to a FORMAT statement.
The final item specified in the I/O statement is the list of
variables.

This is a sequential list of the names of variables and

array elements whose values are to be transferred in the order
indicated.

There is no restriction on the number of names which

may appear in the list of an I/O statement, as long as the total
statement length does not exceed 128 characters.

The modes of the

variables named need not agree with the corresponding FORMAT
statement; however, the modes specified in the FORMAT statement take
precedence.

For example, where A=3.2,J=27,KAL=302, and BOB=7.58:

TYPE 23#A#J#KAL#BOB
FORMAT <I#E#I#E)

The decimal portion of A is dropped and the number 3 is printed
as an integer; the value of J is printed as a normalized number;
KAL is printed as an integer; and BOB is printed as a normalized
number.

The output would look like the following:

0.270000E+2

302

0.758000E+l

6-33

NOTE
In READ and ACCEPT statements, although
the number is read according to the
FORMAT statement, it is stored according
to the mode of the variable. For example:
5
10

ACCEPT l0,A
FORMAT (I)

causes the number 12.3 typed by the user
to be read as 12 and stored as O.120000E+2.
Array names included in I/O lists must be subscripted in one
of the following forms:
A(V)

A (V+C)

A(V-C)

A(C)

where A is the array name, V is a simple integer variable and C is
a positive nonzero integer constant.

TYPE 10,A,I,B,CCI+l),NeJ+l)
FOR~~T CE,I,E,/)

If the list contains more names than there are elements in the
FORMAT statement, the FORMAT statement is reinitialized when the
elements are exhausted.

The first element in the FORMAT statement

then corresponds to the next name in the list.

For instance, in

the preceding example when the value of the variable, B, is printed
in the E format, the control character, slash (/) I causes a carriage
return/line feed to occur.

Then the FORMAT statement is reinitiali-

zed, and the array element, C (I+1), is printed in the E format and
the array element N(J+l) in the I format.

6-34

The list does not have to exhaust the elements of a FORMAT
statement.

If there are fewer names in the list than there are

elements in the FORMAT statement, the program completes the I/O
operation and proceeds to the next sequential FORTRAN statement.
If this next statement is another I/O statement that references a
previously unexhausted FORMAT statement, that FORMAT statement is
reinitialized.

FOruV~T

statements are reinitialized when they are

referenced or when all of their elements are exhausted.
6.7.4

FORMAT Statement
The FORMAT statement controls the arrangement and mode of the

information being transferred.

The values of names appearing in the

I/O statement list are transferred in the mode specified by the
corresponding element in the FORMAT statement.

These controlling

elements consist of the characters E, I, A, slash (/), and quote
(").

The set of elements must be enclosed in parentheses and

separated by commas.

For example:

The control elements E and I are used for defining the mode of
the data being transferred.

When a variable is transferred in the

E format, it is stored or output in floating-point form.

If the

variable is transferred in the I format, it is stored or output in
fixed-point or integer form.

Mode conversion on input or output can

be accomplished because the elements in the FORMAT statement define
the mode of the data.
ridden where necessary.

The mode of the original variable is overFor example:

TYPE 10"A
FORMAT (I)

6-35

The variable, A, is printed as an integer, and the fractional
part of A is truncated.
part, 14, is printed.

If A has a value of 14.96, only the integer
If A has an absolute value of less than one,

zero is printed.
6.7.5

The Format Specification
The control element, A, is used for defining the alphanumeric

mode of data I/O.

When a variable is to be assigned an alpha-

numeric value, data is read one character per'variable.

FORTRAN

ignores CTRL/C, blank tape, RUBOUT, and 0200 code (leader/trailer
tape).

FORTRAN does not see the form-feed character when input is

from the disk.

The decimal equivalent of the ASCII value of the

character is assigned to the variable.
A = 301

(OCTAL)

= 192

For example:
{decimal}

Any variable assigned the alphanumeric value, A, would be set
equal to 192.
It is possible to do arithmetic with integer variables assigned
alphanumeric values.

For example:

DO 10 J=I,S
ACCEPT 12,KCJ)
IF CXCJ)-141) 10 40 10
CONTINUE
"
FORMATCA)

10
12

where the IF statement tests to see if the last character read is a
carriage return (which is ASCII 215 or 141 decimal); if so, control
transfers to Statement 40; if not, control stays within the DO loop.
It is not possible to do arithmetic with real variables assigned
alphanumeric values.

Output in alphanumeric format converts the

value of the variable into an ASCII character and prints that character.

For example:

6-36

FORMAT (A)
DO 20 1=115
TYPE 121AeJ)
CONTINUE

If the variables A(l) through A(S) were not originally assigned
alphanumeric values, the results of the output can be meaningless.
6.7.6

Input Formats
Input data words can only consist of a sign, a decimal value,

an exponent value if the data is floating-point, and a field terminating character such as space.

Any character- that is not a

number, decimal point, sign, or E can be used to terminate a field
except the RUBOUT character.

When typing data, any number of

spaces or other nonnumeric characters can be typed before the sign
or decimal value in order to make the hard copy more readable.
Input data can be transferred into core memory from either the
terminal paper-tape reader, the keyboard, or the high-speed reader.
Input can be entered in either fixed- or floating-point modes
(integers or decimal numbers).

The mode in which data is stored

in core memory is controlled by the first letter of the variable
name.

The characters read into core are determined by the corres-

ponding element in the FORMAT statement.
6.7.6.1

Integer Values--the I Format -- An integer data field con-

sists of sign 2 and up to six decimal characters.

Some examples of

integer values are as follows:

2plus sign can be represented by a plus or space character. Minus
is represented by a minus character.
If a sign character is absent from the data word, the data is stored as positive.

6-37

Typed Numbers

Values Accepted

-2001

-40

-0040

0016
2041

+2041
6.7.6.2

Real Values--the E Format -- A floating-point input word

consists of a sign, the data value up to six decimal characters, an
E if an exponent is to be included, the sign of the exponent, and
the exponent (i.e., the power of ten by which the data word is
multiplied).

For example:

ddd.dddEnn
The d's represent numerical characters in the data and the n's
represent the 2-digit power of ten of the exponent (preceded by a
sign).

Either the sign, the decimal point, or the entire exponent

part can be omitted.

If the sign is omitted, the number is assumed

to be positive; if the decimal point is omitted, it is assumed to
appear after the rightmost decimal character.

If the exponent is

omitted, the power of ten is taken as zero.
Some examples of floating-point values are as follows:
Typed Numbers

6.7.7
6.7.7.1

Values Accepted

0.16 x 10

.16E02

0.16 x 10

1600.E-02

0.16 x 10

2
2
2

OutEut Formats
E and I Formats -- Integer values are always printed as the

sign and a maximum number of four characters with spaces replacing

6-38

leading zeros. On output, integers are left justified within the
stated field. Sufficient trailing spaces are printed to fill the
field followed by one additional space.
Floating-point values are printed in a floating-point format
which consists of sign, leading zero, decimal point, six decimal
characters, the character E, the sign of the exponent (minus or
plus)! and an exponent value of two characters. For example:
Integer Values

Output Format

-1043

-0016
+0016

16
+

Floating-point values are printed as follows:
SO.ddddddEsnn
where:

S represents the sign, minus sign, or space
dddddd represents six decimal digits of the data word

E indicates exponential representatio~
s represents the sign of the exponent value
nn represents the exponent value
Some examples of floating-point output are:
Decimal Value

Output Format

-8,388,608.0

-O.838860E+07

-.000119209

0.119209E-03

6.7.7.2 FORMAT Control Specifications -- In most cases when data is
to be presented; it must be labeled and arranged properly on a data
sheet.

In order that this can be accomplished with FORTRAN, a

6-39

provision has been made so that text information and spacing can be
printed along with the data words. These features are provided by
the special FORMAT control elements quote (") and slash (/). The
slash character causes a return to the left margin.
6.7.7.3 Hollerith Output -- When text information is enclosed in
quotes "and is contained as part of a FORMAT statement, it is output
to the specified device as it appears in the statement. This output
occurs when a TYPE or WRITE statement references a FORMAT statement
containing text, and all other elements of the FORMAT statement
previous to the text have been used. All legal terminal characters
(other than the quote character itself) can be contained within
quotes and output as text.

TYPE 10
FORMAT CI .... THIS IS HOLLERITH .... /)

100

TYPE 100 .. AMIN .. AMAX
FORMAT C/ .... MINIMUM= .... E.. / .... MAXIMUM= .... E.. /)

210

250

TYPE 210
FORMAT (/ ..
CUMULATIVE DISTRIBUTION .... I .. I'
..
I NCREMENTS
FREQUENCY" .. I)
DO 220 K=I .. 100
TYPE 250 .. K.. VALUCL) .. VALUCK+1) .. COUNTCK)
CONTINUE
FORMAT (I.... .. .. E.... .. .. E.... tt .. E.. I)

1....

6.8

IMPLEMENTATION NOTES

6.8.1

Double Subscripts

This version of FORTRAN does not have the facility for doublesubscripted variables. To accomplish double subscripting, the
programmer has to include indexing statements in the source program
as illustrated below. In this example, the matrices are stored
columnwise in memory; that is, sequential locations in memory are
used as follows:

6-40

Element

Relative Position
in Memory (INDX)

all

a2l

a31
a4l

a5l

a6l

a12

a22

a56

a66

If referencing Element a56 in the array, M=5, N=6,
6 by 6 array), and INDX=M+I*(N-l)=5+I*5=35.
a22, INDX=2+6*1=8.

C
C
1

MATRIX MULTIPLY PROGRAM
DIMENSION A(36)~B(36)~C(36)
ACCEPT DIMENSION OF ARRAY
ACCEPT I~I
FORMAT (I)
DO 10 M=I~I
DO 10 N=1 ~ I
I NDX = M+ I

C
2

10
15

DO 20

C
20
C

* (N-1 )

ACCEPT FIRST MATRIX
ACCEPT 1 ~A( INDX>
FORMATCE)
CONTINUE
TYPE 15
FORMAT C/~/~/)
M=l~I

DO 20 N=l~I
I NDX =M+ I * (N-1 )
ACCEPT SECOND MATRIX
ACCEPT 1 ~ BC I NDX)
CC INDX)=0
CONTINUE
MULTIPLY MATRICES

6-41

(1=6 for a

If referencing Element

30
C

40
21

6.8.2

DO 30 M=1,I
DO 30 N=1,I
DO 30 K=l,I
IC=N+I*CM-1)
IA=N+I*CK-1)
IB=K+I*CM-1)
CCIC)=CCIC)+ACIA)*BCIB)
CONTINUE
TYPE 15
PRINT RESULTS IN MATRIX FORM
DO 40 M=1,I
TYPE 21
DO 40 N=1,I
INDX-M+I*CN-l)
TYPE 1, C( I NDX)
CONTINUE
FORMAT C/)
TYPE 15
END
Substatement Feature

The most important result of treating the equal sign as a binary
operator (as explained in Section 6.4.3, Arithmetic Statements) is
that it may be used more than once in arithmetic statement.

In addi-

tion to simple replacement operations (see Section 6.5.3.2, Multiple
Replacement), consider the following:
CPRM:(CKL-CKG)/(CPG=P*(Q+l.»
The internal arithmetic statement (or substatement), CPG=P*
(Q+l), is set off from the rest of the statement by parentheses.
The complete statement is a concise way of expressing the following
common type of mathematical procedure:
Let:

= Ckl - ~g
Cpg

Where: Cpg = P (q+l)

6-42

The stating of a relation followed by the conditions for evaluating any of the variables can be expressed in a single arithmetic
statement in FORTRA~,
A second use of

the equal sign is shown below.

For background
on this short program. i@Q the discussion of the same problem in
the section on the IF $tateroent.
SUM OF THE FIRST 50 INTEGERS
KSUM=0
lNUM=50
KSUM=INUM+KSUM
IF (INUM=INUM-\)3#3#2
STOP

c
2
3

In this example, the s~~ is formed by counting down, but the
same results are achiev§a as in the section on the IF statement.
The initialization is Oflanged so that INUM starts with the value of
50 instead of 0, and th~ §tatement, INUM=INUM+l, is no longer
required.
6.8.3

Error Checking

Because of the extrem@ly compact nature of the FORTRAN-D Compiler, either FORTRAN features or error checking will suffer. In the
case of FORTRAN-O, checkin9 for certain errors is not as important as
preserving the language. ~herefore, the programmer is advised to
follow the rules as stated in this manual and carefully check his
program for mistakes. For example, the statement,
A =B + C will compile, although at

execution time it will give unpredictable

results.

6-43

It should be noted that data areas must not extend below location 5600 in FORTRAN-D.

No diagnostic is issued unless program and

data areas actually overlap.
for data.

words are available
10
Care should be taken not to exceed the limits through use

of large arrays, etc.

A maximum of 896

Similar obvious errors are accepted by the

Compiler; their effects are often unpredictable.
6.8.4

FORTRAN-D Source Program Restrictions
The following limits are imposed upon all FORTRAN-D source

programs:

6.8.4

Not more than 896 data cells. This includes all dimensional variables, user-defined variables, constants, and
all constants generated by the usage of a DO loop.

Not more than 20 undefined forward references to unique
statement numbers per program. An undefined forward
reference is a reference to any statement label that has
not previously occurred in the program. Multiple references to the same undefined statement numbers are considered as one reference.

Not more than 64 different variable names per program.

Not more than 128 characters per input statement.

Not more than 40 numbered statements per program.
FORTRAN-D Compiler and Operating System Core Map

The Compiler occupies the following core locations:
0003-7600

Compiler plus tables

7200-7600

Compiler tables (undefined forward
reference tables, etc.)

The Operating System occupies locations:
0000-5200

Operating System without disk I/O

0000-6000

Operating System for disk I/O

6-44

Locations 5201 through 7576 are available for the user's program
when using paper tape input/output.
6.9

FORTRAN-D ERROR DIAGNOSTICS
Diagnostic procedures are provided in the Compiler to assist the

programmer in program compilation.

When the compiler detects errors

in a FORTRAN source program, it prints the error messages on the user
terminal.

These messages indicate the source of the errors and direct

the programmer's efforts to correct them.

To speed up the Compiler

process, the Compiler prints only an error code.

The programmer then

looks up the error message corresponding to the code in Tables 6-2
through 6-4 and takes the appropriate corrective measures.
6.9.1

Compiler Compilation Diagnostics
Format of Diagnostics

xxxx

+
~The identifying condition code

The number of statements since the appearance
of a numbered statement (octal value) .
------The statement number of the last numbered statement.
For example:
10

A=I(J+l)
B=A*(H+SINFCTHTA)

During compilation of the previous statements, the following
error code would be printed:

6-45

TABLE 6-1
FORTRAN-D STATEMENT SUMMARY
Statement and Form

Explanation

Arithmetic Statements
v = e

v is a variable (possibly subscripted);
e is an expression.

Control Statements
CONTINUE
DO n i=k l ,k 2 ,k

Proceed.
3

END
GO TO n
GO TO (n 1 ' n 2 ' · .. , nn) , i

PAUSE
END

n is the statement number of a CONTINUE; i is an integer variable; klk2k3
are integers or nonsubscripted
integer variables.
Terminate compilation; last statement
in program.
n is a statement number.
nl, ... ,nn are statement numbers; i is a
nonsubscripted integer variable.
e is an expression; nl,n2,n3 are statement numbers.
Temporarily suspend execution.
Terminate compilation; last statement
in program.

Specification Statements
COMMENT
DEFINE DISK

Designated by C as first character on
line.
Enables disk r/o.

DIMENSION vl(n l ), v 2 (n 2 ) , ...
v (n )
n n
FORMAT (sl,s2, ... ,sn)

vl,.:.,v n are variable names; nl, •.. ,nn
are l.ntegers.
s is a data field specification.

Input/Output Statements
ACCEPT f, list

f is a FORMAT statement number; list is
a list of variables; input is from the
terminal.

6-46

Table 6-1.
Statement and Form

(Cont.)
Explanation

READ u,f,list

u is an integer representing the device
which data is to be read:
1= terminal
2=high-speed reader, 3=disk; f is a
FORMAT statement number; list is a list
of variables.

TYPE f,list

f is a FORMAT statement number; list is
a list of variables: output is to the
terminal.

WRITE u,f,list

u is an integer representing device
onto which data will be written: 1=
terminal, 2=high-speed punch, 3=disk,
f is a FORMAT statement number; list is
a list of variables.

l~ ~l

indicating that a statement which occurs one statement octal (one
decimal) after the appearance of Statement 10 is in error.

The

message corresponding to Code 11 shows that the number of left and
right parentheses in the statement is not equal.
If a statement number is referenced but does not appear in the
source program, the diagnostic code will be printed as follows:
xxxx

where the number usually reserved for the last numbered statement
(xxxx) is replaced by the missing statement, e.g.

GO TO 100
The diagnostic would appear as follows where Statement 100 is never
defined.
l~~

6-47

TABLE 6-2
FORTRAN-D COMPILER COMPILATION DIAGNOSTICS
Error
Code
00
01

Explanation
Mixed mode arithmetic expression.
Missing variable or constant in arithmetic expression.

Comma was found in arithmetic expression.
Too many operators in this expression.

Function argument is in fixed-point mode.

Floating-point variable used as a subscript.
Too many variable names in this program.
Program too large, core storage exceeded.
Unbalanced right and left parentheses.

10
11
12
13

14
15

16
17
20
21
22
23
25

Illegal character found in this statement.
Compiler could not identify this statement.
More than one statement with same statement number.
Subscripted variable did not appear in a DIMENSION
statement.
Statement too long to process.
Floating-point operand should have been fixed-point.
Undefined statement number.
Too many numbered statements in this program.
Too many parentheses in this statement.
Too many statements have been referenced before they
appear in the program.
DEFINE statement was preceded by some executable
statement.
Statement does not begin with a space, tab, C, or
number.

6-48

TABLE 6-3
FORTRAN-D COMPILER SYSTEMS DIAGNOSTICS

Error
Code

Explanation

0240

System file error.

3100

Illegal operator on compiler stack.

3417

Preprecedence error.

6204

Error in opening the compiler, FDCOMP.
under account 2.

6211
6463

Error in reading the compiler, FDCOMP.
Error in reading the compiler, FDCOMP.

6731

Disk output error.

6746

No END statement in input file.

6.9.2

The disk may be full.

Must be stored

Compiler Systems Diagnostics
Ce.rtain errors can make it impossible for the Compiler to pro-

ceed in the normal manner.

These errors occur before the Compiler

has been loaded into core.

They may be caused by improperly loading

the Compiler, by not having an END statement on a source file, by a
machine malfunction, or by other errors.

These errors, referred to

as system errors, are explained in Table 6-3.
The compiler may halt (printCTRL/B followed by S) with the PC
set to one of the values listed in Table 6-4 (use the WHERE command
to determine the PC). The file error code will be in the AC.
TABLE 6-4
FORTRAN D ERROR HALTS
PC
Explanation
5004

Error opening FOSSIL. FOSSIL, the FORTRAN operating
system, must be stored under account 2.

5011

Error reading FOSSIL.

6142

Error opening FOSL. FOSL, the FORTRAN operating system loader, must be stored under account 2.

6147

Error reading FOSL.
6-49

6.9.3

Operating System Diagnostics
Not all errors are detected by the Compiler.

only be detected by the operating system (FOSL).

Some errors can
Also there are

some conditions which indicate errors on the part of the Compiler
and/or operating system.

When such an error occurs during running

of a program, the computer prints out an error message containing
the word TILT or ERROR and an error number.
prints

The program then stops,

BS, and returns to the Monitor.
TABLE 6-5
FORTRAN-D OPERATING SYSTEM DIAGNOSTICS

Error
Code

Explanation

Checksum error on FORTRAN binary input.

02
04

Illegal origin or data address on FORTRAN binary input.
Disk input-output error 3 .

High-speed reader error.

Illegal FORTRAN binary input device.

Attempt to divide by zero.

Floating-point input data conversion error.

Illegal op code.

Disk input-putput error 3 .

Non-FORMAT statement used as a FORMAT.

Illegal FORMAT specification.

Floating-point number larger than 2047.

Square root of a negative number.

Exponential negative number.

Logarithm of a number less than or equal to zero.

Illegal device code used in READ or WRITE statement.

3May be caused by machine malfunction or operating system error.

6-50

Table 6-5.
Error
Code
41
76
77

(Cont.)

Explanation
System device full, CQuld not complete a WRITE
statement.
Stack underflow error 4 .
Stack overflow error 4 .

May be caused by source program or loading error; to correct, try
the fOllowing:

a.
b.

Recompile the source program.
Examine source program (in particular the arithmetic statements
and subscripted variables).

6-51

CHAPTER 7
PAL-D ASSEMBLER
7.1

INTRODUCTION
The EduSystem 50 Assembly System is composed of the PAL-D

Symbolic Assembler, LOADER, and ODTHI.

The PAL-D Assembler is used

to translate the user's source program into an object program
(binary or machine code).

LOADER is used to transfer the user's

object program from the disk into core for debugging or execution.
ODTHI (Octal Debugging Technique) is used to dynamically debug the
object program which has been loaded into core using LOADER.
PAL-D (an acronym for Program Assembly Language for the Disk)
is a two pass Assembler (with optional third pass) designed for 4K
PDP-8 family of computers.

A program, written in the PAL-D source

language, is translated by the Assembler into a binary file in two
passes through the Assembler.

The binary file is loaded, boy the

LOADER, into the computer for execution.
During the first pass of the assembly, all user symbols are
defined and placed in the Assembler's symbol table.

During the

second pass, the binary equivalents of the input source language are
generated.

The Assembler's third pass produces a printed assembly

listing of the program's instructions with the location, generated
binary, and source code side by side on each line

To call the

PAL-D Assembler, the user types:
.R PALD

PAL-D responds by requesting INPUT: Type the name of the source
program or programs to be assembled.
7-1

A maximum of three files can

be assembled together.

PAL-D then requests OUTPUT:

Type the name

of the new file in which PAL-D will store the assembled program in
executable binary form.

PAL-D then requests OPTION:

assembly, press the RETURN key.
respons with L.

For a normal

For a listing on the line printer,

If an assembly listing is not desired, respond to

OPTION w·ith N.
PAL-D then proceeds to assemble the program:

any errors in

the program are indicated 7 the program symbol table is printed7 and
finally, an assembly listing of the source program is printed.

When

the listing is completed and the assembly finished, control is
returned to the Monitor.

When PAL-D begins printing the symbol table

at the end of pass 2, the binary file has already been generated.
Thus, the user may type CTRL/C to bypass the symbol table print out.
7.2

EduSystem 50 PAL-D
Because of the necessary hardware changes made for time-sharing

on EduSystem 50, PAL-D has been revised in the following ways (as
differing from PAL-D on a non-timeshared PDP-B) :

7.3

PAL-D, under EduSystem 50, allows a very large number of
user symbols in addition to the permanent symbols listed
in Table 7-1. The permanent symbol table has been revised
to include all instructions peculiar to the time-sharing
system.

A CTRL/C (tC) from the terminal terminates the assembly,
and halts PAL-D, sending the user back to the Monitor.

SYNTAX

Programs processed under PAL-D are written using ASCII characterse

7-2

7.3.1

Legal Characters
The

foll~wing

The alphabetic characters (ABCD .•• XYZ)

"1-

",,'I- _

characters are acceptable to PAL-D:

nwueric characters

1).

".J:Ht:::

Tne special characters

_..

,,"\ ,
\V

&..

-r

c::.

c:..
v

.,
I

Q
"-'

- -

L..-...I

Space

Separates symbols and numbers.

Plus

Combines symbols or numbers (add)

Minus

Combines symbols or numbers (subtract)

Exclamation Mark

Combines symbols or numbers
(inclusive OR)

carriage Return

Terminates a line

-tI

Tabulation

Formats symbols or numbers or
source tape output

Conuna

Assigns symbolic address

Equal Sign

Direct assignment of symbol values

.
I

Semicolon

Terminates coding line (will not
terminate conunents)

Dollar Sign

Indicates end of pass

Asterisk

Sets current location counter:
redefines origin

Point (Period)

Has value equal to current location
counter

Slash

Indicates start of conunent

Ampersand

Combines symbols or numbers (AND)

Quote

Generates ASCII constant

()

Parentheses

Defines literal on current page

Brackets

Defines page 0 literal

7-3

Ignored characters
Form-Feed

Indicates the end of a logical
page of source program

Blank Tape

Used for leader/trailer

Code 200

Used for leader/trailer

Rubout

Follows tabulation characters
for timing purposes

Line-Feed

Follows carriage return and causes
terminal paper to roll upward one
line

Since certain characters are invisible (i.e., nonprinting), the
following symbols are used throughout this chapter to represent their
presence:
Space
Tabulation
carriage Return
7.3.2

Illegal Characters
All characters other than those listed above are illegal when

not in a comment or TEXT field and, being illegal, their occurrence
causes the error message IC (Illegal Character) to be printed by
PAL-D.
7.3.3

Format Effectors
Tabulations are usually used in the body of a source program to

provide a neat page: they can separate fields from one another, as
between a statement and a comment.

For example, a line written

GO, TAD TOTAL/MAIN LOOP
is much easier to read if tabs are inserted to form
TAD TOTAL

7-4

/MAIN LOOP

Either the

11:11

(semicolon) or ")" (carriage return-line feed)

character may be used as a statement terminator.

The semicolon is

considered identical to carriage return-line feed except that it
will not terminate a comment.

Example:

TAD A

ITHIS IS A COMMENT; TAD B

The entire expression between the "/" (slash) and ~(carriage
return) is considered a comment.
The semicolon also allows the programmer to place several lines
of coding on a single line.

If, for example, he wishes to write a

sequence of instructions to rotate the contents of the accumulator
and link six places to the right, it might look like

RTR .;
RTR~

RTR .;

The programmer may place all three RTRs on a single line by separating them with the special character "i" and terminating the line
with a carriage return.

The above sequence of instructions can then

be written
RTR; RTR; RTR
This format is particularly useful when setting aside a section of
data storage for a list.

For example, a 12-word list could be

reserved by specifying the following format.

7-5

0; 01 01 01 01 0
at
m; 01 01 01 0

A neat printout (or program listing) makes subsequent editing,
debugging, and interpretation much easier than when the coding is
laid out in a haphazard fashion.
7.4

NUMBERS
Any sequence of numbers delimited by a punctuation character is

interpreted numerically by PAL-D.
The radix control pseudo-operators (pseudo-ops) indicate to the
Assembler the radix to be used in number interpretation (see Section
7.9).

The pseudo-op DECIMAL indicates that all numbers are to be

interpreted as decimal until the next occurrence of the pseudo-op
OCTAL.

The pseudo-op OCTAL indicates that all numbers are to be

interpreted as octal until the next occurrence of the pseudo-op
DECIMAL.
The radix is initially set to octal and remains octal unless
otherwise specified.
7.4.1

Arithmetic and Logical Operators
The arithmetic and logical operators are:

Plus

2s complement addition (modulo 4096)

Minus

2s complement subtraction (modulo
4096)

Exclamation Mark

Boolean inclusive OR (union)

7-6

Ampersand

Boolean AND (intersection)

Space

Interpreted as inclusive OR when
used to separate ~~o symbolic
operators. Example:
TAG,

7.4.2

Evaluating Expressions
Symbols and numbers (exclusive of pseudo-op symbols) may be

combined by using the arithmetic and logical operators to form expressions.

7 •5

Expressions are evaluated from left to right.

Example:

A+B

A-B

AlB

A&B

value

0002

0003

0005

7777

0003

0002

Value

0007

0005

0014

0002

0007

0005

Value

0700

0007

0707

0671

0707

0000

STATEMENTS
PAL-D source programs are usually prepared on a terminal with the

aid of the Editor as a sequence of statements.

Each statement is

written on a single line and is terminated by a carriage return-line
feed sequence.

PAL-D statements are virtually format free; that is,

elements of a statement are not placed in numbered columns with rigidly
controlled spacing between elements, as in punched-card oriented
assemblers.
There are four types of elements in a PAL-D statement which are
identified by the order of appearance in the statement, and by the
separating, or delimiting character which follows or precedes the
element.

7-7

statements are written in the general form
label, operator operand

/comment

The Assembler interprets and processes these statements, generating
one or more binary instructions or data words, or performing an
assembly process.

A statement must contain at least one of these

elements and may contain all four types.
7.5.1

Labels
A label is the symbolic name created by the source programmer

to identify the position of the statement in the program.

If present,

the label is written first in a statement and terminated by a comma.
7.5.2

Operators
An operator may be one of the mnemonic machine instruction codes

(Tables 7-1 &7-2),or a pseudo-operation (pseudo-op) code which directs
assembly processing.
Section 7.9.

The assembly pseudo-op codes are described in

Operators are terminated with a space if an operand

follows or with a semicolon, slash, or carriage return.
7.5.3

Operands
Operands are usually the symbolic address of the data to be

accessed when an instruction is executed, or the input data or arguments of a pseudo-oPe

In each case, interpretation of operands in a

statement depends on the statement operator.

Operands are terminated

by a semicolon, a slash if a comment follows, or a carriage returnline feed.

7-8

7.5.4

comments
The programmer may add notes to a statement following a slash
Such comments do not affect assembly processing or progrfuu

mark.

execution, but are useful in the program listing for later analysis
or debugging.
7,,6

SYMBOLS
The programmer may create symbols to use as statement labels,

as operators, and as operands.

A symbol is a string of one or more

alphanumeric characters delimited by a punctuation character.

symbol contains from one to six characters from the set of 26 alphabetic characters and ten digits 0 through 9; however, the first
character must be alphabetic.
7.6.1

Symbol Distinction
The PAL-D Assembler makes a distinction between the types of

symbols it is processing.
a.

Permanent symbols
JMS

A symbol whose value of 4000(octal) is taken from
PAL-Dis permanent operation code symbol table.

User-defined symbols

HERE

7.6.1.1

These types are

A user-defined symbol; when used as a symbolic
address tag, its value is the address of the
statement it tags (this value is assigned by PAL-D) •

Permanent Symbols

PAL-D has in its permanent symbol table definitions of its
operation codes, operate commands, and many input-output transfer (lOT)
microinstructions (see table 7-2.).

PAL-D g s permanent symbols may

be used without prior definition by the user.
7-9

7.6.1.2

User-Defined Symbols

User-defined symbols are composed according to the following
rules.
a.

The characters must be alphabetic (A-Z) or numeric (0-9) .

The first character must be alphabetic.

Only the first six characters of any symbol are meaningful
to PAL-Dj the remainder, if any, are ignored.

Note that because of the third rule above, a symbol such as INTEGER
would be interpreted as INTEGE since the seventh character is ignored.
Remember, if symbols of more than six characters are used, the programmer must avoid defining two apparently different symbols whose
first characters are identical.

For example, the two symbols

GEORGEl and GEORGE2 differ only in the seventh character, thus the
Assembler treats them as being the same symbol, GEORGE.
When the symbol following the space is a user-defined symbol,
the space acts as an address field delimiter.

Example:

*2117
CLA

•
•

•

JMP A

where A is a user-defined symbol with the value 2117.

JMP A is evaluated as follows.

7-10

The expression

JMP

Address A

101

000

000 (binary representation of
permanent symbol JMP)

000

all

001

III (binary representation of
address A)

The operation codes (op codes) are inclusively ORed to form
JMP A

101 all 001 III

or written more concisely in octal as 5317.
7.6.2

S\~bolic

Addresses

A symbol used as a label to specify a symbolic address must appear
first in the statement and must be immediately followed by a comma.
When used in this way, a symbol is said to be definede

A defined

symbol can reference an instruction or data word at any point in the
program.

A symbol can be defined as a label only once.

If a program-

mer attempts to define the same symbol as a label again, the second
or successive attempt is ignored and an error is indicated.
Assembler recognizes only the first definition.

These are legal

symbolic addresses:
ADDR,
TOTAL,
SUM,

The following symbolic addresses are

~llegal:

7ABC,

(first character must be alphabetic)

LAB ,

(comma must immediately follow label)

7-11

The

7.6.3

Symbolic Operators
Symbols used as operators must be predefined by the Assembler or

by the programmer.

If a statement has no label, the operator may

appear first in the statement, and must be terminated by a space, tab,
semicolon, or carriage return.

The following are examples of legal

operators:

7.6.4

TAD

(a mnemonic machine instruction operator)

PAGE

(an Assembler pseudo-op)

ZIP

(legal only if defined by the user)

Symbolic Operands
Symbols used as operands must have a value defined by the user.

These may be symbolic references to previously defined labels where
the arguments to be used by this instruction are to be found, or the
values of symbolic operands may be constants or character strings.

TOTAL#

TAD AC1+TAG

The values of the two symbols ACl and TAG, already defined by
the user, are combined by a two's complement add.

This value is

used as the address of the operand.
7.6.5

Symbol Tables
The Assembler processes symbols in source program statements by

referencing its symbol tables which contain all defined symbols along
with the binary value assigned to each symbol.

7-12

Initially, the Assembler's permanent symbol table contains the
mnemonic op codes of the machine instructions and the Assembler
pseudo-op codes; as listed in tables 7-1 and 7-2=

As the source

program is processed, symbols defined in the source program are added
to the user's symbol
7.6.6

table~

Direct Assignment statements
The programmer inserts new symbols with their assigned values

directly into the symbol table by using a direct assignment statement
of the form
symbol = value
where the value may be a number or expression.

For example,

ALPHA=5
HETA=17

A direct assignment statement may also be used to give a new
symbol the same value as a previously defined symbol.

BETA=17
GAMMA=BETA

The new symbol, GAMMA, is entered into the user's symbol table with
the value 17.
The value assigned to a symbol may be changed.

ALPHA=7
changes the value assigned to the first example from 5 to 7.

7-13

The user may also define symbols by use of the comma.

When the

first symbol of a statement is terminated by a comma, it is assigned
a value equal to the current location counter (CLC).

*100
CLA
JMP A

For example,

/SET CLCCORIGIN) TO 100

DCA B

The symbol TAG is assigned a value of 0100, the symbol B a value of
0102, and the symbol A a value of 0103.
Direct assignment statements do not generate instructions or
data in the object program.

These statements are used to assign values

so that symbols can be conveniently used in other statements.
7.7

ADDRESS ASSIGNMENTS
The PAL-D Assembler sets the origin, or starting address, of the

source program to absolute location (address) 0200 unless the origin
is specified by the programmer.

As source statements are processed,

PAL-D assigns consecutive memory addresses to the instructions and
data words of the object program.

This is done by incrementing the

location counter each time a memory location is assigned.

A statement

which generates a single object program storage word increments the
location counter by one.

Another statement may generate six storage

words, thus incrementing the location counter by six.

7-14

TABLE 7-1
EDUSYSTEM 50 SYMBOL LIST
Code

Operation

Mnemonic

Event Time

Memory Reference Instructions
0000

AND

Logical AND

1000

TAD

Twos complement add

2000

ISZ

Increment and skip if zero

3000

DCA

Deposit and Clear AC

4000

JMS

Jump to subroutine

5000

JMP

Jump

6000

lOT

7000

OPR

Operate

Group 1 Operate Microinstructions
7000

NOP

No operation

7001

lAC

Increment AC

7004

RAL

7006

RTL

Rotate AC and link left one
Rotate AC and link left two

7010

RAR

Rotate AC and link right one

7012

RTR

Rotate AC and link right two

7020

CML

Complement link

7040

CMA

Complement AC

7100

CLL

Clear link

7200

CLA

Clear AC

7-15

Table 7-1.
Code

Mnemonic

(Cont. )
Event Time

Operation

GrouE 2 °Eerate Microinstructions
7402

HLT

Halts the computer

7404

OSR

Inclusive OR switch register with AC

7410

SKP

Skip unconditionally

7420

SNL

Skip on nonzero link

7430

SZL

Skip on zero link

7440

SZA

Skip on zero AC

7450

SNA

Skip on nonzero AC

7500

SMA

Skip on minus AC

7510

SPA

Skip on plus AC (zero is positive)

Combined 0Eerate Microinstructions
7041

CIA

Complement and increment AC

7120

STL

Set link to 1

7204

GLK

Get link (put link in AC, bit 11)

7240

STA

Set AC

7604

LAS

Load AC with switch register

= -1

PSEUDO-OPERATORS
DECIMAL

OCTAL

EXPUNGE

PAGE

FIELD

PAUSE

FIXTAB

TEXT

XLIST
Z

7-16

Direct assignment statements and some Assembler pseudo-ops do
not generate storage words and therefore do not affect the location
counter.
7.7.1

Current Address Indicator
The special character • (point or period) always has a value

equal to the value of the current location counter.

It may be used

as any integer or symbol (except to the left of an equal sign).
Example:

*200
JMP .+2

is equivalent to JMP 0202.

Also,

*300
.+2400

will produce in location 0300 the quantity 2700.

Consider

*2200

CALL=JMS I •
0027

The second line, CALL=JMS I .does not increment the current location
counter, therefore, 0027 is placed in location 2200 and CALL is placed
in the user's symbol table with an associated value of 4600 (the octal
equivalent of JMS I).

7-17

7.7.2

Indirect Addressing
When the character

appears in a statement between a memory

reference instruction and an operand, the operand becomes the address
containing the address of the statement to be executed.

Consider

TAD 40

which is a direct address statement, where 40 is interpreted as the
address containing the quantity to be added to the accumulator.

Thus,

if address 40 contains 0432, then 0432 is added to the accumulator.
Now consider
TAD I 40

which is an indirect address statement, where 40 is interpreted as
the address of the address containing the quantity to be added to the
accumulator.

Thus, if address 40 contains 432, and address 432 con-

tains 456, then 456 is added to the accumulator.
Then a reference is made to an address not on the same page as
the reference, PAL-D sets the indirect bit (bit 3) of the machine
instruction, generating an indirect address linkage to the off-page
reference (see Paging and Off-Page Referencing, sections 7.8.1.1 and
7.8.1.2) •
In the case of several off-page references to the same address,
the indirect address linkage will be generated only once.

7-18

Example:

*2117

CLA
•
e

•

*2600

TAD A
•

•
•

DCA A

The space preceding the user-defined symbol A acts as an address field
delimiter.

PAL-D will recognize that the address tag A is not on the

current page (in this case 2600-2777) and will generate a link to it
in the ~ollowing manner.
1777

In location 2600, PAL-D will place the word

(octal equivalent of TAD I 2777)

and in location 2777 (the last location on the current page) the word
2117 (the actual address of A) will be placed.

When it sees the second

reference to A it will use the previous link word rather than creating
a new one.
PAL-D will recognize and generate an indirect address linkage
only when the address referenced is to a location on another page,
not the current page.

The programmer must use the character I to

indicate an explicit indirect address when indirectly addressing to a
location on the current page.

7-19

PAL-D cannot generate a link for an instruction that is already
specified as being an indirect address.

In this case, PAL-D will type

the error message II (Illegal Indirect) i the error message is ignored
and assembly is continued.
7.7.3

Autoindexinq
Interpage references are often necessary for obtaining operands

when processing large amounts of data.

The PDP-8 computers have

facilities to ease the addressing of this data.

When absolute loca-

tions 10 to 17 (octal) are indirectly addressed, the content of the
location is incremented before it is used as an address and the incremented number is left in the location.

This allows the programmer to

address consecutive memory locations using a minimum of statements.
It must be remembered that initially these locations (10 to 17)
must be set to one less than the first desired address.

Because of

their characteristics, these locations are called auto index registers.
No incrementation takes place when locations 10 to 17 are addressed
directly.

Example:
statement is in location 500
Data is on the page starting at 5000
Autoindexing register 10 is used for addressing

0476
0477
0500

1377
3010
1410

•
•
•

•

0577

•

~D (5000-1)
DCA 10
TAD I 10

ISET UP AUTO INDEX
IWITH 4777
IC(t0) IS INCREMENTED TO 5000 BEFORE
lIT IS USED AS AN ADDRESS

•

4777

ILITERAL GENERATED BY PAL-D

7-20

When the statement in location 500 is executed, the content of location 10 will be incremented to 5000 and the content of location 5000
will be added to the content of the accumulator.

If the instruction

TAD I 10 is re-executed, the content of location 5001 is added to the
content of the accumulator: and so on.
7.7.4

Literals
Symbolic and integer literals (constants) may be defined as shown

below:
C~

TAD (2)
DCA INDEX

Operator and operand must always
be separated with a space.

The left parenthesis is a signal to the Assembler that the integer
following is to be assigned a location in the table at the top of the
current page.

This is the same table in which the indirect address

linkages are stored.

In the above example, the quantity 2 is stored

in the first free location in a list beginning at the top of the current page (relative address 177), and the statement in which it appears
is encoded with an address referring to that location.
A literal is assigned to storage the first time it is encountered:
subsequent references will be to the same location.
If the programmer wishes to assign literals to page 0 rather than
the current page, he must use square brackets, ( ], in place of paren-

7-21

theses.

Whether using parentheses or square brackets, the right or

closing member is optional and may always be replaced with a carriage
return.
TAD (777

Nesting - Literals may be nested as shown below.
*200
TAD(TAD(30

will generate

0200

1276

•

•
•
•

•

0376
0377

1377
0030

(literals assigned to locations
0377 and 0376: top of current page)

This type of nesting may be carried to many levels.
Literals are stored on each page starting at relative address
177 (only 127 10 or 1778 literals may be placed on page 0).

literals are being generated for some nonzero page and then the origin
is set to another page, the current page literal buffer is punched
out during pass 2.

If the origin is reset to the previously used

page, the same literal will be generated if used again.
If a single character is preceded by a quote ("), the 8-bit value
of the ASCII code for that character is inserted instead of taking the
letter as a symbol.

7-22

Example:

CLA
TAD ("A

will place the constant 0301 in the accumulator.
7.8

INSTRUCTIONS
There are two basic groups of instructions:

and augmented.

memory reference

Memory reference instructions require an operandi

augmented instructions do not require an operand.
7.8.1

Memory Reference Instructions
In PDP-8 computers, some instructions require a reference to

memory.

They are appropriately designated memory reference instruc-

tions, and take the following format.
OPERATION
CODES o-~

MEMORY
PAGE

r--'---..

I I · I I I · I I I ' I . I· I I"I
0

INDIRECT
ADORE SSING

ADDRESS

Memory Reference Instruction Bit Assignments
Bits 0 through 2 contain the operation code of the instruction to be
performed (such as AND,TAD,

or JMP).

Bit 3 tells the computer if

the instruction is indirect, that is, if the address of the instruction
specifies the location of the operand, or if it specifies the location
of the address of the operand.

Bit 4 tells the computer if the instruc-

tion is referencing the current page or page zero.
5 through 11 (7 bits) to specify an address.

7-23

This leaves bits

In these 7 bits, 200

octal or 128 decimal locations may be

specified~

the page bit increases

accessible locations to 400 octal or 256 decimal.
The address field of a memory reference instruction may be any
valid expression.

Example:
A=270
*200

TAD A-20

produces, in location 200, the word
1250
which in binary is

001

010

0000

101

which is also TAD 250 •
•
7.8.1.1

Paging

To ease the programmer's addressing problems, a convention has
been defined that devides memory into sectors called pages.

Each page

contains 200 octal locations (128 decimal) numbered 0 to 177 (octal)
on that page.
37 (octal).

There are 40 octal or 32 decimal pages numbered 0 to
Some examples of page numbers and the absolute and

relative locations (addresses) are shown below.

It must be borne in

mind, however, that there is no physical separation of pages in memory.

Page

0
1

2
36
37

Absolute
Address

0-177
200 - 377
400 - 577
7400 - 7577
7600 - 7777

7-24

Relative
Address

0- 177
0- 177
0-177
o - 177
o - 177

The following table offers a comparison of specific absolute
and relative addresses on the same page.

Page
f'\

3
12
31
37

Absolute
Address

Reiative
Address

617
2577
6255
7777

17
177
55
177

Since only seven bits are necessary to address 200 octal locations, bits 5 to 11 are reserved for this function.
7.8.1.2

Off-Page Referencing

The page on which an absolute address is contained can be determined from bit 4 of the instruction.

If bit 4 is a 0, the address

refers to a location on page 0; if bit 4 is a 1, the address refers
to a location on the current (same) page, that is, the same memory
page as the instruction.
7.8.2

Augmented Instructions
Augmented instructions are divided into two groups:

operate and

input-output transfer microinstructions.
7.8.2.1

Operate Microinstructions

within the operate group there are two groups of microinstructions.
Group 1 microinstructions are principally for clear, complement, rotate,
and increment operations and are designated by the presence of a 0 in
bit 3 of the machine instruction word.

7-25

(See table 7-1.)

ROTATE
AC Alii 0 L

ROTATE 1
POSITION If A 0,
2 POSITIOIII'S

RIGHT

If A ,

n n n,N"1

OPERATION
CODE 7

CLA

CONTAIIII$

CIoIIA

Cll

Cloll

A 0 TO

lAC

RJTATE

AC AND L

LEfT

SPECify

GROUP'

Group 1 Operate Microinstruction Bit Assignments
Group 2 microinstructions are used principally in checking the
content of the accumulator and link and, based on the check, continuing to or skipping the next statement.

Group 2 microinstructions are

identified by the presence of a 1 in bit 3 and a 0 in bit 11 of the
machine instruction word.

(See table 7-1.)

CO'lTAINS AI
TO SPfClf Y
GROUP 2

SMA

SI\IL

COI\ITAII\IS A 0

TJ5P£C<'
GROuP 2

Group 2 Operate Microinstruction Bit Assignments
Group 1 and group 2 microinstructions can not be combined because
bit 3 determines only one or the other.
within Group 2, there are two groups of skip instructions.

They

may be referred to as the OR group and the AND group.
OR Group

AND Group

SMA
SZA
SNL

SPA
SNA
SZL

The OR group is designated by a 0 in bit 8, the AND group by a 1 in
bit 8.

OR and AND group instructions cannot be combined because bit

8 determines only one or the other.

7-26

If the programmer does combine legal skip instructions, it is
important to note the conditions under which a skip may occur.
a.

OR Group - If these skips are combined in a statement, the
inclusive OR of the conditions determines the skip.
SZA SNL

The next statement is skipped if
the accumulator contains 0000, or
the link is a 1, or
both conditions exist.
b.

AND Group - If the skips are combined in a statement, the
logical AND of the conditions determines the skip.
SNA S,ZL

The next statement is skipped only if the accumulator differs from 0000 and the link is o.
7.8.2.2

Input-output Transfer Microinstructions

These microinstructions

ini~iate

operation of peripheral equip-

ment and effect information transfer between the central processor
and the input-output device (s).

This is the principal function of

the input-output transfer (lOT) microinstructions.

Table 7-2 lists

all valid lOT microinstructions, and each is discussed in detail in
Chapter 11.

7-27

TABLE 7-2
EDUSYSTEM 50 lOT INSTRUCTION SUMMARY
Number

Function

Instruction

Program Control

6200

CKS

Check Status

6402

DUP

Duplex Console

6403

UNO

Unduplex Console

6405

CLS

Clear Status

6411

URT

User Run Time

6412

TOO

Time of Day

6413

RCR

Return Clock Rate

6414

DATE

Date

6415

SYN

Quantum Synchronization

6416

STM

Set Timer

6417

SRA

Set Restart Address

6420

TSS

Skip on TSS/8

6421

USE

User

6422

CON

Console

6430

SSW

Set Swtich Register

6431

SEA

Set Error Address

6440

ASD

Assign Device

6442

REL

Release Device

7402

HLT

Halt

7404

OSR

OR With Switch Register

6406

SEGS

Segment Count

6600

REN

Rename File

6601

OPEN

Open File

6602

CLOS

Close File

6603

RFILE

Read File

File Control

7-28

Table 7-2.

(Cont.)

Number

Instruction

6604

PROT

Protect File

6605

WFILE

Write File

6610

CRF

Create File

6611

EXT

Extend File

6612

RED

Reduce File

6613

FINF

File Information

6614

SIZE

Segment Size

6616

WHO

Who

6617

ACT

Account Number

Function

Input Buffer Control
6030

KSR

Read Keyboard String

6031

KSF

Skip on Keyboard Flag

6032

KCC

Clear Keyboard Flag

6034

KRS

Read Keyboard Buffer Static

6036

KRB

Read Keyboard Buffer Dynamic

6400

KSB

Set Keyboard Break

6401

SBC

Set Buffer Control Flags

Output Buffer Control
6040

SAS

Send A String

6041

TSF

Skip On Teleprinter Flag

6042

TCF

Clear Teleprinter Flag

6044

TPC

Load Teleprinter and Print

6046

TLS

Load Teleprinter Sequence

Hish-SEeed PaEer TaEe Reader and Control
6010

RRS

Read Reader String

6011

RSF

Skip On Reader Flag

6012

RRB

Read Reader Buffer

6014

RFC

Reader Fetch Character

7-29

Table 7-2.
Number

(Cont.)
Function

Instruction

High-Speed Paper Tape Punch and Control
6020

PST

Punch String

6021

PSF

Skip On Punch Flag

6022

PCF

Clear Punch Flag

6024

PPC

Load Punch Buffer and Punch Character

6026

PLS

Load Punch Buffer Sequence

DECtape Control
6764

DTXA

Load Status Register A

6771

DTSF

Skip On Flags

6772

DTRB

Read Status Register B

6660

LST

Print String

6662

LCF

Clear Printer Flag

6661

LSF

Skip on Printer Flag

6664

LLC

Print Character

6666

LPC

Print Character

6632

RCRA

Read Card, Alpha

6634

RCRB

Read Card, Binary

6636

RCRC

Read Card, Compressed

Line Printer

Card Reader

Disk Cartridge
6743

DLAG

Perform Disk Transfer

6772

RDS

Read Device Status

7-30

7.9

PSEUDO-OPERATORS
The progra~er may use pseudo-operators (pseudo-ops) to direct

the Assembler to perform certain tasks or to interpret subsequent
coding in a certain manner~

Some pseudo-ops generate storage words

in the object program, other pseudo-ops direct the Assembler on how
to proceed with the assembly.

Pseudo-ops are maintained in the

Assembler=s permanent symbol table.
The function of each PAL-D pseudo-op is described below.
7.9.1

Current Location Counter
The programmer may use the PAGE pseudo-op to reset the current

location counter (CLC) to the first location on a specified page.
PAGE

without an argument, the CLC is reset to the first location on the next succeeding page. Thus, if a program is
being assembled into page 1 and the programmer wishes to
begin the next segment of his program on page 2, he need
only insert PAGE, as follows.
JMP .-7

PAGE
CLA
PAGE n

(First location on page 2)

resets the CLC to the first location of page n, where n
is an integer, a previously defined symbol, or a symbolic expression. Example:
(sets the CLC to location 400)
(sets the CLC to location 1400)

PAGE 2
PAGE 6
7.9.2

(Last location used on page 1)

Extended Memory

When using more than one memory bank, the pseudo-op FIELD instructs
the Assembler to output a field setting.
where n is an integer, a previously defined s}~bol, or a symbolic expression within the
range of 0<n<7.

FIELD n

7-31

This pseudo-op causes a field setting (binary word) of the form
11 XXX 000

where 000<xxx<111

to be output on the binary file during pass 2.

This word is inter-

preted by the Loader, which then begins loading information from the
file

into the new field.

(Field settings are ignored by TSS/8

LOADER.)
7.9.3

RADIX Control
Integers used in a source program are usually taken as octal

numbers.

If, however, the programmer wishes to have certain numbers

treated as decimal, he may use the pseudo-op DECIMAL.

7.9.4

DECIMAL

all integers in subsequent coding are taken as decimal until the occurrence of the pseudo-op OCTAL.

OCTAL

resets the radix to its original octal base.

Listing Control
During pass 3, a listing of the source program is printed.

The programmer may, however, control the output of his pass 3 listing
by use of the pseudo-op XLIST.
XLIST

7.9.5

Those portions of the source program enclosed by XLIST
will not appear in the pass 3 listing.

Text Facility
The pseudo-op TEXT enables the user to represent a character or

string of characters in ASCII code trimmed to six bits and packed two
characters to a word.

The numerical values generated by TEXT are left-

justified in the storage words they occupy, with the unused bits of
the last word filled with Os.

7-32

A string of text may be entered by giving the pseudo-op TEXT
followed by a space, a delimiting character, a string of text, and

the

s~~e delL~iting

character.

Exa~ple:

TEXT ATEXT 5THI NGA

The first printing character following TEXT is taken as the delimiting
character, and the text string is the characters which follow until
the delimiting character is again encountered.
If the example above were at location 0200, the pass 3 listing
would be as follows.

0200
0201
0202
0203
0204
0205

2405
3024
4023
2422
1116
0700

TEXT ATE
XT
S
TR

(L-I denotes a space)

IN
GA

NOTE
with TEXT, any printing character
may be used as a delimiting character;
the delimiting character cannot be
used in the text string.
7.9.6

End of Program
The special symbol $ (dollar sign) indicates the end of a pro-

gram.

When the Assembler encounters the $, it terminates the pass.

7.9.7

End of File
The pseudo-op PAUSE signals some assemblers to stop processing

the current input file.

TSS/8 PAL-D ignores any PAUSE statements.

7-33

7.9.8

Altering the Symbol Table
PAL-D has a permanent symbol table which contains all instruc-

tions

(symbols and their octal values) required by EduSystem 50.

They

are referred to as PAL-D's basic instructions or symbols, and are
listed in tables 7-1 and 7-2.
When the symbolic program to be assembled required instructions
not already in the table (e.g., card reader lOT's), the table must be
altered to include those instructions.

PAL-D has two pseudo-ops that

are used to alter the permanent symbol table:
EXPUNGE

deletes the entire permanent symbol table, except
pseudo-ops.

FIXTAB

appends symbols to the table for duration of the
assembly. All symbols defined before the occurrence
of FIXTAB are temporarily made part of the permanent
symbol table.

These pseudo-ops can be used to eliminate unneeded symbols from the
table, thus providing more storage for user symbols.
To append the following card reader lOT's to the symbol table,
the programmer generates an ASCII file containing:
RCSF=6631
RCSP=6671
RCRD=6674

FIXTAB
This file is then included as one of the input files to PAL-D.

(Only

the last input file should contain a dollar sign.)
7.9.9

Internal Representation
Each permanent and user-defined symbol occupies four words

tions)

in the symbol table storage area, as shown below:

7-34

(loca-

012

II II I

Wo'rd 1
Word 2
I
Word 3

C x 45 + C
2
8
1
C x 45 + C
4
8
3

C~ x 45 R + C

...

Word 4

first 2 characters

second 2 characters
third 2 characters
octal code or address

where CI , C ' .•. C represent the first character, second character, ••. ,
6
2
sixth character resprectively.
(Symbols may consist of from one to
six characters.)
system flags.

Bits 0 and 1 of word 1 and bit 0 of word 2 are

with a permanent symbol, word 4 contains the octal code

of the symbol; with a user-defined symboli word 4 contains the address
of the symbol.

For example:

the permanent symbol TAD is represented

as follows.
Word 1

248 x 45 + 01
8

Word 2

04 x 45 + 00
8
8

Word 3

1345

2248 + 4000

= 42248 D

~flag bit

= 0000

Word 4 = 1000

(octal code for TAD)

Note that the first degit of the ASCII octal code for each character
is always trimmed by the assembler so that the character is represented using six bits of a word.

For example, ASCII code for T is 324,

it was trimmed to 24: A is 301, it was trimmed to 01: etc.
7.10

PROGRAM PREPARATION AND ASSEMBLER OUTPUT
The source language file is prepared using the Editor.

7.10.1

program File

Since the Assembler ignores certain characters, these may be used

7-35

freely to produce a more readable symbolic source file.

These useful

characters are tab and form-feed.
The Assembler will also ignore extraneous spaces, carriage returnline feed combinations, and rubouts.
The program body consists of statements and pseudo-ops.
program is terminated by the dollar sign ($).

The

If the program is

large, it may be split into as many as three files.

This often

facilitates editing the source program since each section is physically smaller.
The Assembler initially sets the origin (current location counter)
of the source program to 0200.

The programmer may reset the current

location counter by use of the asterisk.
The following two programs are identical except that format
effectors were used in the second printout.

*200
/EXAMPLE OF FORMAT
BEGIN~ 0/START OF PROGRAM
KCC
KSF/WAIT FOR FLAG
JMP .-l/FLAG NOT SET YET
KRB/READ IN CHARACTER
DCA CHAR
TAD CHAR
TAD MSPACE/IS IT A SPACE?
SNA CLA
HLT/YES
JMP BEGIN+2/NO: INPUT AGAIN
CHAR~ 0/TEMPORARY STORAGE
MSPACE~ -240/-ASCII EQUIVALENT
/END OF EXAMPLE
$

7-36

*200
IEXAMPLE OF FORMAT
BEGIN"

KCC
KSF
JMP
KRB
DCA
TAD
TAD

ISTART OF PROGRAM
IWAIT FOR FLAG

/FLAG
SET YET
IREAD IN CHARACTER

• -1

CHAR
CHAR

MSPACE lIS IT A SPACE?
SNA CLA
HLT
IYES
JMP
BEGIN+2 INO: INPUT AGAIN
CHAR,
o
ITEMPORARY STORAGE
MSPACE, -240
I-ASCII EQUIVALENT
lEND OF EXAMPLE
$

Both of these programs will produce the same binary code.

The second,

however, is easier to read.
7.10.2

Assembly

PAL-D is a two-pass assembler with an optional third pass which
produces a side-by-side assembly listing of the symbolic source statements, their octal equivalents, and assigned absolute addresses.
passes are invisible to the user.

These

However, the user determines whether

or not the third pass will be made by his response to PAL-D's OPTION:
query (see section 7-11).
7.10.3

Pass 1

During pass 1, PAL-D processes the source (file) and places in
its user's symbol table the definitions of all symbols used.

7-37

The

userDs symbol table is printed at the end of pass 2.
remain undefined at the end of pass 1, the US

If any symbols

(Undefined Symbol)

diagnostic is printed during pass 2 when the undefined symbol is encountered (see Error Diagnostics).

The symbol table is printed in

alphabetical or er on the terminal.

If the program listed above were

assembled, PAL-D would output the following symbol table.

BEGIN

7.10.4

0200

CHAR

0213

MSPACE 0214

Pass 2

During pass 2, PAL-D processes the source or file and generates
binary output using the symbol table equivalences defined during pass
1.

The binary output may be loaded in core by LOADER.
The binary coded file consists of leader code, an origin setting,

and data words.

Every occurrence in the source program of an asterisk

causes a new origin setting in the binary output.

At the end of the

binary coded file, a binary checksum is produced and trailer code is
generated.
7.10.5

Pass 3

During pass 3, PAL-D processes the source file and prints out a
side-by-side listing of the generated octal code and the original
source language.

If the program shown above were assembled, the pass

3 listing would be:

7- 38

0200
0201

0000

0202

603i
5202

0203
0204
0205
0206
0207
0210
0211
0212
0213
0214

*200
IEXAMPLE OF FORMAT
BEGIN"
0
KCC
KSF
JMP
.-1
KRB
DCA
CHAR
TAD
CHAR
TAD
MSPACE
SNA CLA

6032

6036

3213
1213
1214
7650
7402
5202
0000
7540

ISTART OF PROGRAM
IWAIT FOR FLAG
IFLAG NOT SET YET
IREAD IN CHARACTER
I I5

IT A SPACE?

HLT
/YES
JMP
BEGIN+2 INO: INPUT AGAIN
CHAR ..
0
ITEMPORARY STORAGE
MSPACE .. -240
I-ASCI I EQUIVALENT
lEND OF EXAMPLE

'BS

7.11

OPERATING THE PALD ASSEMBLER
Assembling with PAL-D in TSS/8 requires no operator intervention

between passes.

The symbol table is typed out at the end of pass two

and the listing at the end of pass three.
nated at any point by typing CTRL/C.

The assembly may be termi-

control will revert from PAL-D

to the Monitor program which will type out a dot (e) and wait for the
next instruction from the terminal.

In the illustrations which follow,

non-underlined characters are those typed out by the system; underlined
characters represent user-supplied data.

T~e

sharing assemblies are

requested as follows.
In response to the monitor's dot

the user types the command, a space and the name of the system
program.
.R PALO

PAL-D is brought into core and signals its readiness by requesting
an input file name.
INPUT:TYPE
7-39

The user reply in this case was BIN2, a user symbol for a source
program to be assembled. PAL-D next requests the name of an
output file.
OUTPUT:TYPEB
The user response was TYPE2, the name under which the assembled
program will be stored. Optionally, the user may type the RETURN
key to specify no output file.
OUTPUT:
This is useful in debugging. A program may be corrected and
reassembled any number of times with production of an output
file postponed until a satisfactory version is achieved. PAL-DiS
final query is whether the user wants a program listing.
OPTION:
There are three effective responses only: N signifying No, L
signifying a listing on the Line printer, and J (RETURN key)
signifying a listing on the terminal. When it receives the final
response, PAL-D reads in the user source program from disk (source
programs are stored prior to assembly) and proceeds with the
assembly. After assembly, PAL-D returns control to the Monitor
which types
tBS

•

and waits for the user to supply the next command.
NOTE
Under the TSS/8 Monitor PAL-D does not require a dollar
sign ($) as the last entry in a source program, but if it
does not find one it types a message to warn the user
that his program may not be assembled properly by an
assembly program other than time-sharing PAL-D.
The following listing was reproduced from a time sharing run.
It illustrates the initial dialogue, the symbol table produced at the
end of pass 2 (any error messages would also appear at this point) and
the listing, in octal notation, produced during pass 3.

7-40

f·~ PALO

INITIAL
DIALOGUE

SYMBOL
TABLE

I NPliT : R J "'2

QUTPlIT:TyP?
OPTION:

rCOlINT

0415

l~~;~
IT

V14i7

(1(

RFG
START

~1 40 F:(1425
0416
(Ii 4 ~H1

IPk OGk.l\M
*C1400

PROGRAM
LISTING

0400
0401
0402
0403
0404
0405
0406
0407
0410
0411
0412

7200
4217
1377
3215
1376
3216
1216
4225
2216
2215

0413

4?17
7402
0000

vM17

0"'(tH~

0420
0421

1375
4225
1374
4225
5617
0000
6(146
6041
5227

LITERALS

0423
0424
0425
042 f,
0427
0430
0431
0432
0574
0575

It'0577
l576

LOOP,

CLA
JMS CRLF
TAD (-12
DCA COUNT
TAD (26(1
DCA kEG
TAD REG
Jt'-'S OUT
ISZ REG
ISZ COlINT
JMP LOOP
JIVS CKLF
HLT

COUNT,
kEG,
CRLF,

52(1f,

0414
0415
0416

v'422

START,

V1 vl00

72V10
5 f,? 5

TO TYPE aliT .. 1 23 45 6 18 9"

FOR ZERO

0
0

TAD (21 5
JMS OUT
TAD <212
JMS OUT
JMP I CRLF
OUT,

IASC I I

TLS
TSF
JMP • - 1
CLA
J:v,p I OUT

0212
0215
0260
7766

t8S

7-4i

IASC I I FOk CARRIAGE kETUt<N
IASC I I FOR LINE FEED

7.12

ERROR DIAGNOSTICS
PAL-D makes many error checks as it processes source language

statements.
message.

When an error is detected, the Assembler prints an error

The format of the error messages is
ERROR CODE

ADDRESS

where ERROR CODE is a two-letter code which specifies the type of
error, and ADDRESS is either the absolute octal address where the error
occurred or the address of the error relative to the last symbolic tag
(if there was one) on the current page.
The programmer should examine each error indication to determine
whether correction is required.
PAL-Dis error messages are listed and explained below.
Error
Code

Explanation

Two PAL-D internal tables have overlapped - This situation
can usually be corrected by decreasing the level of literal
nesting "or number of current page literals used prior to
this point on the page.

Systems device error - An error was detected when trying
to read or write the system device; after three failures,
control is returned to the Monitor.

Systems device full - The capacity of the systems device
has been exceeded; assembly is terminated and control is
returned to the Monitor.

Illegal character - An illegal character was encountered
in other than a comment or TEXT field; the character is
ignored and the assembly continued.

Illegal redefinition of a symbol - An attempt was made
to give a previously defined symbol a new value by other
means than the equal sign; the symbol was not redefined.

7-42

Illegal eguals - An equal sign was used in the wrong
context. Examples:
TAD A +=B (the expression to the left of the equal
sign is not a single symbol or, the
expression to the right of the equal
A+B=C
sign was not previously definedj

Illegal indirect - An off-page reference was made: a
link could not be generated because the indirect bit
was already set. Example:

*200
TAD I A .;

PAGE';
A, 7240 ~

The program terminator

Current nonzero page exceeded - An attempt was made to
a. override a literal with an instruction, or
b. override an instruction with a literal: this can be
corrected by
(1) decreasing the number of literals on the page or
(2) decreasing the number of instructions on the page.

Symbol table exceeded - Assembly is terminated and control
is returned to the Monitor.

Undefined symbol - A symbol has been processed during
pass 2 that was not defined before the end of pass 1.

Page 0 exceeded - Same as PE except with reference to
page O.

7-43

$; is missing=

CHAPTER 8
UTILITY PROGRAMS

8.1

SYMBOLIC EDITOR
The EduSystem 50 Symbolic Editor (EDIT) provides the user with

a powerful tool for creating and modifying source files online.

Its

precise capabilities and commands are detailed in Introduction to
Programming, Chapter 5.

EDIT allows the user to delete, insert,

change, and append lines of text, and then obtain a clean listing of
the updated file.

EDIT also contains commands for searching the file

for a given character.
EDIT considers a file to be divided into logical units, called
pages.

A page of text is generally 50-60 lines long, and hence

corresponds to a physical page of program listing.

A FORTRAN-D

program is generally 1-3 pages in length: a program prepared for
PAL-D may be several pages in length.

EDIT operates on one page of

text at a time, allowing the user to relate his editing to the
physical pages of his listing.

EDIT reads a page of text from the

input file into its internal buffer where the page becomes available
for editing.

When a page has peen completely updated, it is written

onto the output file and the next page of the input file is made
available.

EDIT provides several powerful commands for paging through

the source file quickly and conveniently.
NOTE
The end of a page of text is marked by a
form feed (CTRL/L) character.
Form feed
is ignored by all EduSystem 50 language
processors.

8-1

To call the Editor, type:

.R EDIT
EDIT responds by requesting INPUT:

Type and enter the name of

the source file to be edited.

If a new file is to be created using

EDIT, there is no input file.

In this case, strike the RETURN key.

EDIT then requests OUTPUT:
to be created.

Type the name of the new, edited, file

The name of the output file must be different from

the name of the input file.

If EDIT is being called to list the

input file, there is no need to create an output file; strike the
RETURN key.

When EDIT sets up its internal files and is ready for a

command, it rings the bell on the terminal.
For example:

.R EDIT
INPUT:WXZOLD
OUTPUTtXYZNEW
8.2

(Bell rings at this point.)

LOADER
LOADER is used to load programs in BIN format from a disk file

into the user's core area for execution.

These files in BIN format

can be created by PAL-D in the course of an assembly or they can be
loaded from paper tape using PIP or PUTR (see the PIP section for
special instructions on loading BIN format tapes).
To call LOADER, type:

.R LOADER
LOADER responds by asking for INPUT:
name of the file or files to be loaded.

Respond by entering the
Although many System Library

Programs allow multiple input files, the LOADER uses this feature to

8-2

TABLE 8-1
SYMBOLIC EDITOR OPERATIONS SUMMARY
Special Characters
carriage Return (RETuRN KEY)

Fu.."1ction
Text fvlode

Enter the line in the

buffer.
CTRL/C

Text Mode - Same as form feed.

CTRL/U

Text Mode - Cancel the entire line of
text, continue typing on next line.
Command Mode - Cancel command. Editor
issues a ? and carriage return/line feed.

Equal Sign (=)

Command Mode - Used in conjunction with
• and / to obtain their value {for
example, type .=}.

Form Feed (CTRL/L Combination)

Text Mode - End of inputs, return to
command mode.

Left Angle Bracket «)

Command Mode - List the previous line
(equivalent to .-lL).

Line Feed

Text Mode - Used in SEARCH command to
insert a CR/LF combination into the
line being searched.

(~)

Right Angle Bracket {>}

Command Mode - List the next line
I\

eq'" .; "7'alen4- 4-0
\04 ..... V

......

•

..L
1 T.i..i )
I
....

•

Rubout

Text Mode - Delete from right to left
one character for each rubout typed.
Does not delete past the beginning of
the line. Is not in effect during a
READ command.
Command Mode - Same as CTRL/U.

Slash (/)

Command Mode - Value equal to number of
last line in buffer. Used as argument
(as in /-S,/L) •

Tabulation (CTRL/TAB Key
Combination)

Text Mode - Produces a tabulation
which, on output, is interpreted as
spaces.

8-3

TABLE 8-2
EDIT COMMAND SUMMARY
Command

Format

Meaning

APPEND

Append incoming text from keyboard to any
already in the buffer until a form feed is
encountered.

CTRL/C

Stop listing and return to Command Mode.

CHANGE

Delete line n, replace it with any number
of lines from the" keyboard until a form
feed is entered.

m,nC

Delete lines m through n, replace from keyboard as above until form feed is entered.

Delete line n of the text.

m,nD

Delete lines m through n inclusive.

END

Output the contents of the buffer. Read
any pages remaining in the input file,
outputting them to the output file.
When
everything in the input file has been moved
to the output file, close it out and return
to the Monitor. E is equivalent to a
sufficient number of N's followed by a T
command.

GET

Get and list the next line beginning with
a tag.

INSERT

Insert before line I all the text from
the keyboard until a form feed is entered.

Insert before line n until a form feed is
entered.

KILL

Kill the buffer (i.e., delete all text lines).

LIST

List the entire buffer.

List line n.

m,nL

List lines through n inclusive.

MOVE

m,n$kM

Move lines m through n inclusive to before
line k.

Output the entire buffer and a form feed,
kill the buffer and read the next page.

DELETE

8-4

Table 8-2.
COIDIDand

(Cont.)

Format

Meaning

Repeat the above sequence n timese

Output the contents of the buffer to the
output file, followed by a form feed.

Output line n, followed by a form feed.

m,nP

Output lines m through n inclusive
followed by a form feed.

READ

Read text from the input file and append
to buffer until a form feed is encountered.

Search the entire buffer for the character
specified (but not echoed) after the
carriage return. Allow modification when
found.
Editor outputs a slash (/) before
beginning a SEARCH.

Search line n, as above, allow modification.

m,nS

Search lines m through n inclusive, allow
modification.

PROCEED

TERMINATE

special advantage.

Close out the output file and return to the
Monitor.

Because it loads the files in the order they are

typed, LOADER can be used to load patches and overlays.
requested INPUT, LOADER requests OPTION:

After it has

For normal operation strike

the RETURN key; LOADER is able to load any part of core, except locations 7767 - 7777.If the program to be loaded is to be debugged,
respond to OPTION: with D.

This will cause OOTHI to be loaded along

with the input files and started. OOTHI indicates that it is ready by
printing a second line feed. OOTHI uses locations 4 and 7000 - 7777;
and if loaded along with a program which uses any of these locations#
the result is unpredicatble.

8-5

Example 1:

Normal Operation

.R LOADER
INPUTIMAIN~

PATCH1~

PATCH2

OPTION:
'BS

Example 2:

Load ODT with Input File

.R LOADER
I NPU T: PROG 1
OPTION: D

As seen in the first example, LOADER returns control to Monitor
when it is finished.

The user can then start the program by using

the Monitor command START.

For example, LOADER can be used to load

and run the short program given as an example in the section on PAL-D.

• R LOADER
INPUT: EI N2
OPTION:
'BS
.START 400
0123456789

'ES
NOTE
All BIN format files loaded by LOADER
include a checksum.
If LOADER detects a
checksum error while loading, it prints
LOAD ERROR and terminates the load.
8.3

OCTAL DEBUGGING TECHNIQUE

(ODTHI)

ODTHI is a powerful octal debugging tool for testing and modifying
PDP-8 programs in actual machine language.

It allows the user to

control the execution of his program and, where necessary, make
immediate corrections to the program without the need to reassemble.

8-6

The complete command repertoire of ODT is documented in Introduction to programming, Chapter 5.

ODTHI (on EduSystem 50) is the

high-core version which resides in locations 7000 through 7777.
The paper-tape output commands of regular ODT are not available in
EduSystem 50 ODT.

To call ODTHI, the user types:

.LOAD 2 ODTHI 0 7000
.START 7000
If ODTHI is to be used to de~ug a program being loaded with
LOADER, ODTHI can be loaded and started directly by specifying the
Debug (D) option to LOADER.
ODTHI executes an SRA (Set Restart Address) as part of its initialization process.
ODTHI.

As a result, typing CTRL/C always returns control to

If the program being debugged sets up its own restart address,

typing CTRL/C transfers control to the new restart address.

It is

necessary to type tBS followed by START 7000 to force control back
to ODTHI.

Every time ODTHI regains control, it puts the terminal in

duplex mode.

Users debugging programs which do not operate in duplex

mode, should be aware of this fact.
ODTHI saves the state of the delimiter mask, when it regains
control via a breakpoint.

The state of this mask is restored on a

continue (C) command, but not on a GO (G) command.
8.4

CATALOG (CAT)
The Monitor maintains a library of disk files for each user.

The System Library Program CAT is used to obtain a catalog of the
contents of this library.

For each file, CAT prints the size of the

file in units of disk segments.

The size of a disk segment is 256

(decimal) words of disk storage.

The protection code for the file is

also given.

(See the section on Advanced Monitor Commands for a

8-7

TABLE 8-3
ODT COMMAND SUMMARY
Command

Meaning

Open for modification, the register in which the contents of AC were wtored when the breakpoint was
encountered.

Remove the breakpoint.

nnnnB

Establish a breakpoint at location nnnn.

Back Arrow (....)
(SHIFT/O)

Close register, open indirectly.

Proceed from a breakpoint.

nnnnC

continue from a breakpoint and iterate past the breakpoint nnnn times before interrupting the useros
program at the breakpoint location.

nnnnG

Transfer program control to location nnnn.

Illegal Character

Current line typed by user is ignored, ODT types ?CR/LF.

LINE FEED

Close register and open the next sequential one for
modification.
Open the search mask register, initially set to 7777.
It may be changed by opening the search mask register
and typing the desired value after the value typed by
ODT, then closing the register.

LINE FEED

Close search mask register and open next register
immediately fotlowing, containing the location at
which the search begins.
It may be changed by typing
the lower limit after the one typed by ODT, then
closing the register.

LINE FEED

Close lower search register, open next register containing the upper search limit initially set to 7000
(location of ODT).
It may be changed by typing
the desired upper limit after the one typed by ODT and
closing the register with a carriage return.

RETURN

Close previously opened register.

Reopen latest opened register.

8-8

Table 8-3. (Cont.)
Meaning

Command

Open register designated by the octal number nnnn.

nnnn/
ITT"\
'-'J:'

n. rr"".,

(.
,
\, I

"'''' ........ ....,,,,,

Close register, take contents of that register as
a memory reference and open it.

(SHIFT/N)

Search the portion of core as defined by the upper
and lower limits for the octal value nnnn.

nnnnW

precise explanation of protection codes.)

If the program was created

by any of the System Library Programs, it has a protection code of
12, meaning that other users can read the file, but only the owner
can change it.

To call CAT, type:

.R CAT
The CAT program then prints a listing similar to the one shown
below and concludes by printing tBS and exiting to the Monitor •
• R CAT
DISK FILES FOR USER

3,,13 ON

NAME
SIZE
FIE
.BIN
1
PROG .FCL
2
INTER .BAS
1
BAS000.TMP
1
BASI00.TMP
1
INT2 .BAC
1
FCLPRG.FCL
2

DATE
3-JUN-70
9-JUN-70
9-JUN-70
9-JUN-70
9-JUN-70
9-JUN-70
9-JUN-70

PROT
17
12
17
17
17
37
12

TOTAL DISK SEGMENTS:

9-JUN-70

tBS

8.5

SYSTEM STATUS (SYSTAT)
It is frequently useful to know the status of the system as a

whole; how many users are on-line, where they are, what they are
8-9

doing, etc.

The SYSTAT program provides this capability.

To call

SYSTAT, type:
.SYSTAT
or, to produce a listing on the line printer,
.SYSTAT:L
SYSTAT responds by printing on the first line:
the Monitor being run, the time, and the date.

the version of

SYSTAT then reports

the uptime which is the length of time in hours, minutes, and
seconds since the system was last put on-line.
SYSTAT then lists all on-line users.
by his account number.

Each user is identified

The job number assigned to him and the number

of the console he is using are indicated, as is the particular
program he is running.

The state of each user is indicated, whether

he is running (RUN), not running (tBS) or waiting for something.

a user has byped CTRL/S to stop his printing, tS will be printed;
otherwise tQ will be printed.

The amount of computer time used by

each user since he logged in is given.
If more users are on-line than the system has core fields to
hold them, the fact that the system is swapping is reported.

The

number of free core blocks used internally by the Monitor for Terminal
buffering and various other purposes is printed.

Then SYSTAT reports

any unavailable devices, i.e., devices which are assigned to individual users.

The job to which they are attached is also indicated.

Finally, the number of available segments of disk storage is reported.
A sample SYSTAT listing is shown below.
printing tBS and exiting to the Monitor.

8-10

SYSTAT terminates by

.SYSTAT
STATUS OF TS5/8.24 DEC PDP-8 '1 AT 16:03&32 ON

9 DEC 74

UPTIME 00:03:32
WHO

WHERE

WHAT

,
t

0; 3

43~21

K04
K00

SYSTAT
PIP

JOB

AVAILABLE CORE

BUSY DEVICES

NONE

284

FREE CORE=319

FREE DISK SEGMENTS

8-11

STATUS

RUNTIME

RUN

00:00:02

KEY

fQ
tQ

00100i10

CHAPTER 9
PROGRAMS FOR HANDLING DATA
9.1

PERIPHERAL UTILITY TRANSFER ROUTINES

(PUTR)

PUTR (Peripheral Utility Transfer Routines) is a utility program used to transfer files between all TSS/8 devices.
PUTR can
perform most of the functions of the programs PIP and COpy which
operated under the previous version of the TSS/8 Monitor.

The

following is a list of TSS/8 devices used by PUTR.
Device Names
CDR:

Card Reader

Dn: or DTAn:

DECtape:

KBD:

Terminal Keyboard/Reader

LPT:

Line Printer

PTP:

High-Speed Paper Tape Punch

PTR:

High-Speed Paper Tape Reader

RKAn: or RKBn:

RK~5: OS/8

SYS:

TSS/8 user file area

TTP:

Terminal Punch

TTY:

Terminal Printer

9.1.1

Disk Monitor, COPY, OS/8, or PUTR

file structure

PUTR Commands
PUTR Commands are entered at the terminal in response to the

asterisk which is printed at the left margin.

A command may be

typed with a command string of the form:
*command device:output files

9-1

= device:input files

If a mistake is made while typing a PUTR command, there are
three special characters which help correct the situation.
RL~OL~

Typing

(or DELETE) deletes characters from the end of the line,

printing the deleted characters.

Typing a LINE FEED causes the com-

mand line to be printed on the user's terminal without executing
it, and typing CTRL/U deletes the entire line.
Commands to PUTR can be abbreviated; however most cannot be
abbreviated with less than three characters.

PUTR commands and

their purposes are listed below in alphabetical order.
COpy

Copy files.

DELETE

Delete files.

DIRECTORY

List directories of file structured devices.

EXIT

Returns to TSS/8 Monitor.

LIST

List files on the line printer (LPT).

PUNCH

Punches files on the high-speed punch_

TAPE

Punches files on the terminal punch.

TYPE

Types files on terminal (TTY).

ZERO

Zeroes RK¢5 to OS/8 format.
PUTR format.

Zeroes DECtape to

Examples of these commands are given in the following paragraphs.
Examples:
.R

purn

*COpy DTA0IFOO.SAV=FOO.SAV
This will copy the file FOO.SAV from the system area onto DTA¢.

9-3

NOTE
The DECtape mounted on DTA¢: must be
either PUTR format or OS/8 format.
PUTR cannot write onto the Disk Monitor
or COpy format DECtapes.
To make a PUTR formatted tape use the ZERO Command which is
described below.
DECtapes.

PUTR can only read Disk Monitor and COpy format

This means that the user must convert any such tape that

he may wish to write on.
following procedure.

To convert a tape the user may use the

First, mount an empty tape on unit ¢.

Then

mount the tape to be converted on unit I and type the following:
.R PUTR
*ZERO DTA0a
ARE YOU SURE?
YES
*Copy DTA0:=DTA1:

This will move all the files from DTAI:
mat) to DTA¢:

(COpy or Disk Monitor for-

(PUTR format).

PUTR is a very powerful p~ogram, as these examples illustrate.
An "*" in a command line says that any name will match.

*COpy DTA0a=*.BAS
This command line will cause all files with the extension .BAS to be
put onto the DECtape on unit ¢.
• DELETE •• TMP

The command line will delete all files on your system area with
extension .TMP.
9-4

*DEL 111

This command will delete all files whose names are three characters or less in length.

The "?" is called a "wild card".

This

character will match on any character in its position.
*DEL ABD1

This may be used to delete all files with names which are 3 or
4 characters in length and with ABD as the first three characters.
*DEL *

This will delete all files on your system area.

ZERO cannot

be used for the system disk.

*DELDTA0:*

This could be used if the DECtape on unit ~ were an OS/8 format
tape and if the user wanted it to remain an OS/8 format tape. A
ZERO command would change it to a PUTR format tape.
*TYPE ABC

This will type the file ABC on the terminal.

This file is

assumed to be a TSS/8 format ASCII file.
*LIST DTA0:FILE.LS/OS8
This will list an OS/8 format ASCII file on the line printer.
OS/8 and TSS/8 character formats are different, and, therefore,
character conversion switches have been added to PUTR.

9-5

NOTE
TSS/8 character files can be stored on
OS/8 DECtapes and RK¢5 diskpacks.
It
is not necessary to do character conversions if the user is not going to
use the file on OS/8. The following is
an example of a command line which may
be used if one wishes to use a file
under OS/8.

*COpy RKA01*.PA/OSa=YILE/TS8
This will put FILE.PA on RKA¢:, converting it from TSS/8 format
to OS/8 format.

switches on the output (left) side indicate how

characters are to be packed.

Switches on the input (right) side

indicate how characters are to be unpacked.
NOTE
There is a compatability problem between
TSS/8 and OS/8. OS/8 needs a CTRL/Z at
the end of ASCII files. Since no TSS/8
programs insert this CTRL/Z, most OS/8
programs cannot work with ASCII files
generated by TSS/8 and converted by PUTR.

*LIST YOO
is equivalent to

*COpy LPT,zFOO/TS8
*LIST FOO/BAS
This will list a BASIC program on the LPT.

*COPY FOO.BAS/BAS=PTR:
This will take an ASCII paper tape of a program and create a
BASIC program file called FOO.BAS.

9-6

When creating a BASIC file using

PUTR, the input must be valid and in increasing line-number order, or
BASIC will not be able to process it.
NOTE
The Paper Tape Reader handler will print
a U t ll and will wait for a carriage return
to be typed to indicate the paper tape is
ready. The default program names on PTR:
and CDR: are "NONAME".

*COpy DTA0tFOOePAL/TS8=CDR:/026
This will create a TSS/8 3-for-2 packed ASCII File from the card
reader; DEC ¢26 card code.
NOTE
¢26 is the default switch for the card
reader.

*COpy PROGeBAS/BAS=CDR:
This will create a BASIC program file from the card reader
(¢26 code) •
Additional notes:
Files on the TSS/8 system disk are unique only in their file
names.

Files on DECtape and RK¢5 are unique in file name and exten-

sion.

This means that the user can have the files FOO.BAS and

9-7

FOO.BAC ON DECtape or R~5 but not on the TSS/8 system disk. Files
may be copied from other user areas only if the user knows the name
of the file'. The following is an example of this.

*COpy DTA0IMYFILE.BAS=HISFILE[1#12l
9.1.3. - Card Reader: END-OF-FILE, Hung Device
An end of file on the card reader is indicated by a card with a
/* in columns 1 and 2, with the rest of the card blank.
If the card reader should have a hardware error, i.e., pick fail,
or if it runs out of cards, the Monitor prints out the hung device
message. When this happens, type "START". At this point, PUTR will
ask "BAD CARD, TRY AGAIN?II. The user may answer by typing either
IIN" followed by a carriage return to cause an end of file on the card
reader, a carriage return only if it is desired to continue reading
cards (after fixing the status of the card reader), or CTRL/C to
give up. The error message above will also print out if 39,40, or
80 columns were not read.
If this happens, place the card which was
just read at the bottom of the deck to be re-read.
9.2 - COPY COMMAND
The general format for the COpy command is:
*COPY (dev :]

output name

input name

[extension]

[iswitche~ [=J [dev:J

f!switche~

[ext]

Items in large brackets are optional. One of II '- ", "=,., or "(
must be used to separate the output and input file descriptors. Up
to six input file descriptors may be specified (separated by commas).
The default output and input devices (dev:) are SYS:. The default
output and input extensions are * (to be explained).
II

9-8

The switches on the output side indicate the type of character
packing (default is IMAGE). Switches on the input side indicate the
type of character unpacking (default is image).
n[p,Pn]" is the
account number where the file is located. This is only applicable to
+-'I-I"'11r a file name; all
input from SYS: • If a device is -~"'''''~+=';.o~
the files on that device will be selected. The asterisk (*) can be
i::)tJc~..L.L...L~"'"

TaT;
"

. . . \..,.'" "''\,J """ "-

used either for the file name or the extension, or both.
input side, all file names or extensions will match.

If used on

NOTE
A user may not reference another user's
file directory. Therefore, asterisks (*)
and wild cards (?) cannot be successfully
used when an account number is given.
The asterisk on the output side uses the file name or the
extension of the file opened on the input side.
CAUTION
TSS/8 system files are unique in name only,
whereas DECtape and RK~5 files are unique
in name and extension.
It is possible to have the files FOO.BAS and FOO.BAC on a DECtape
or RK¢5 but not under the same account number on the system disk.
Storing FOO.BAS on the system disk will delete any file named FOO,
for example FOO.BAC.
The question mark (?) is a wild card character which is similar
to the asterisk (*), except that it matches any character in its
position.

The question mark cannot be used on TSS/8 extensions since

these extensions are internal numbers rather than character extensions.

9-9

Examples of COpy Commands:

*COpy FOO=D0rFOO.BAS

Copies FOD.BAS from
(same extension).

D~:

to SYS:
.

*COpy *=D0:*.BAS

Copies all files with .BAS extensions from D~: to SYS:

*COpy *=D0:A .. a .. c

Copies A,B,C from D~: to SYS:
(same name and extension).
Copies all files from Dg: with
the extension .Ase to files on
SYS: with same name but with the
extension .THP.

*COpy *.ASC/TS8=D0IFOO.AS/OS8

Converts an OS/8 character format
to TSS/8 format while copying a
file from D~: to the system disk,
SYS: .
Saves all files from SYS: onto

*COpy 00: =*

D~:

NOTE
If DECtape is used for output, it must
be either a PUTR structure or OS/8 type
tape, and not a Disk Monitor or COPY tape.
9.1.1.1

ZERO Commands

Format
Zeroes DECtape directories to
PUTR file structure.

*ZERO Dn: or
*ZERO DTAn:

Zeroes

*ZERO RKAn: or

RK~5

to OS/8 file structure.

*ZERO RKBn:
After typing a ZERO command, PUTR will ask "ARE YOU SURE?"
N for YES or NO, as the case may be.

9-10

Type Y or

9.1.1.2

DELETE Command

Format
*DELETE

dev:

name

ext.

, more files

NOTE
If the user wishes to zero his account
he may type the following command line.
*DELETE *

The following command line may be used
to zero OS/8 DECtapes and to preserve
the OS/8 file structure.
*DELETE Dn: or
*DELETE DTAn:
9.1.1.3

DIRECTORY Commands
Format

*DIRECTORY [dev:] name [.ext] or
*DIRECTORY [dev:]
Example:
*DIRECTORY (carriage return)
This command line will give a directory listing of all files
on your disk area (SYS:).

*DIR D0I/LPT

This command will give a directory listing of the DECtape on
unit ¢.

The listing will be printed on the line printer, if it is

available.
9-11

Please note that directory listings of the Monitor, and COpy
format tapes.will include just the names and extensions.

*DIR * .BAS

This will make a directory listing of the files on SYS: that
have the extension .BAS.
9.1.1.4

LIST Command

Examples:

*LIST FOO
*LIST BASPRO/BAS
*LIST D0ILIST.LS/OSB

The LIST command changes the default input switch from /IM to
/TS8 and sets in the default output device, LPT:.
identical to "*COPY LPT:=FOO/TS8
9.1.1.5

"LIST FOO

11
•

TYPE Command

The TYPE command is identical to the LIST command except that
the output device is TTY:.

LIST" and "TYPE

will insert a carriage

return/line feed in the output when the line length for the LPT: or
TTY: is exceeded and will not output RUBOUTs.
line feeds for every form feed it sees.

"TYPE" will insert 4

If the text that exceeds the

line limit for the device need not be printed, then the /TRIM switch
should be'appended to the file descriptor.

*TYPE FOO/TRIM

9-12

For example,

9.1.1.6

PUNCH Command

The PUNCH command "*PUNCH name" is equivalent to:
*COPY PTP:=name/TS8
9.1.1.7

TAPE Command

The TAPE command "*TAPE name" is equivalent to:
*COpy TTP:=name/TS8
Both PUNCH and TAPE will punch LEADER/TRAILER on the tapes.
following are examples:
*PUNCH FOO

(TSS/8ASCII Format)
(BASIC Format)(SAVE Format)

*PUNCH BASPRG/BAS
*PUNCH SAVPRG/SAV

9.1.1.8

The

EXIT Command

This is the command which will enable the user to exit from
PUTR.
Example:
*EXIT
fBS

or
*E
tSS

9.1.1.9

Special Notes

BINARY PAPER TAPES
No switch is required to punch a binary tape. However, if the
binary is an OS/8 file /058 will be required. Binaries on TSS/8 and
9-13

05/8 are stored the same way that ASCII files are stored on their
respective systems.
When a binary tape is read use the /TS8 switch or the /OS8 switch
on the output side of the COpy Command, and /BIN on the input side.
/BIN tells the input to compute a checksum on the tape.
Examples:
*COpy TSFILE.BIN/TS8=PTRI/BIN
*COpy D010SFILE.BN/OS8=PTRI/BIN
SAVE FORMAT PAPER TAPES
Punch the tape, with /SAV on the input file descriptor, using
PUNCH or TAPE.
Example:
*PUNCH SAVFIL/SAV

When reading the tape, read it with /SAV on the input side.
Example:
*COPY FOO.SAV=PTRI/SAV
/SAV and /BIN should not be mixed on the same command line.
Example of bad switch use:
*PUNCH FOO/SAV~F002/BIN
NOTE
Typing CTRL/C will cause PUTR to return
to the "*".
If PUTR is in the process
of copying files, the file that is currently being transferred will not be
completely transferred.
Therefore, the
user should delete the last name which
PUTR printed.

9-14

9.1.1.10

Default propagation

When more than one file description is included on the input
side of a PL~R co~mand; then any parameters not specified in one
file description are the sa~e as those of the previous description:
Example:
*LIST DTA0IA#B#C
This will list the files A, B, and C from DTA¢.
*LIST A#DTA0:B#DTA1:C
This will list the files A from SYS: (the user's file area), B
from DTA¢:, and C from DTAI.

A similar rule also applies to switches.

To list two OS/8 files from DTA¢:, do NOT type
*LIST DTA0:A#B/OS8
for the /OS8 will apply only to file B.

Rather, type

*LIST DTA0:A/OS8#B
The /OS8 will now apply to both file A and file B.
Using CTRL/O
While PUTR is transferring files, it prints the name of each
input file as it begins reading it.
by typing CTRL/O.

This print-out can be disabled

The print-out can be re-enabled by typing a

carriage return.

9-15

9.1.1.11

DECtapes and RK%5 Disk

DECtapes can be Disk Monitor, COPY, OS/8, or PUTR file structure
tapes.

PUTR will know which tape is mounted.

on the Disk Monitor or COpy DEct·apes.

PUTR will not write

However, it will read them so

that the user may update his tapes if necessary.
OS/8 file structure format.

The RK%5 is in

RK%5 is divided into two logical de-

vices, RKAn: and RKBn: where n is the drive number

(~-3).

RKAn: is

the first half of the disk, and RKBn: is the second half of the disk.
Each of the writeable devices Dn:, RKAn:, and RKBn: has directory
space for up to 240 entries.
PUTR format.

A ZERO operation on DECtapes zeroes to

A ZERO operation on RKAn: or RKBn: zeroes to OS/8 format.
NOTE
The data format of the files is independent of the file structure. This means
that TSS/8 files can be put on an 08/8
type device without any conversion. Any
ASCII or binary file that will be used by
the OS/8 or TSS/8 systems should have the
appropriate switches (/OS8 or /TS8) while
copying.
It is also helpful when storing
both formats (/OS8 and /TS8) on the same
device, that you use TSS/8 type extensions
(.BIN, .ASC, .BAS) for the TSS/8 type
files and OS/8 type extensions (.BN, .AS,
.BA .•• ) for the OS/8 type files.

9-16

9.1.2

TSS/8 FILE EXTENSIONS

Internal Number

File Extension

9.1.3

.ASC

ASCII

.SAV

SAVE

.BIN

BINARY

. BAS

BASIC SOURCE

.BAC

BASIC COMPILED

.FCL

FOCAL SOURCE

.TMP

TEMPORARY

Blank - required by System.

.DAT

DATA FILE (BASIC)

.LST

LISTING FILE

• PAL

PAL SOURCE

UNASSIGNED

PUTR SWITCHES
Switches for all devices:
1M

IMAGE transfer; no conversion

6BIT -

Six Bit ASCII packed 2 characters/word

X240 -

Excess 240, 2 characters/word

X237 -

Excess 237, 2 characters/word

OS8

OS/8, 3 characters/2 words

TS8

TSS/8, 3 characters/2 words

BAS

TSS/8 BASIC format

Paper Tape Switches
BIN

Binary check summing

SAV

Save format with check summing
9-17

Card Reader Switches
ALP

RCRA, 6 bit internal alpha.

COM

RCRC, compressed 8 bit (PDP8-E systems)

~26

to ASCII

~29

to ASCII

Line Printer and Terminal
TRIM -

9.2

Trims off excess line.
(NOTE: a carriage return /line feed will be
inserted in a line that is too long for the
device if TRIM is not specified.)
LPT
List on line printer if available (DIRECTORY
command only).
PERIPHERAL INTERCHANGE PROGRAM (PIP)
Disk is a convenient storage medium for many files; however, it

may be more useful to keep some programs on paper tape.

PIP provides

a convenient means of transferring files between disk and paper tape,
for those users who wish to preserve copies of their files off-line.
9.2.1

PIP Conventions
PIP may be considered a link between disk file storage and

paper-tape devices.

To punch a desired file, PIP obtains that file

from the disk and punches it on paper tape.

Similarly, to load a

paper tape, PIP inputs the tape from the reader, then outputs it to
a disk file.
The way files are named is important to PIP.
always named.

Files on disk are

Paper tapes, on the other hand, have no names as far

as the system is concerned (although the user can label the physical
tape in any manner he chooses).

Paper tapes never have file names;

therefore, PIP uses the absence of a file name to indicate a paper
tape (absence of a file name is indicated by striking the RETURN key).

9-18

The way in which INPUT: and OUTPUT: is indicated provides the
means for determining the direction of file transfer. If PIP is to
get its input from the disk, the input is a file name; if the input
is from a paper tape; no file name is given. Similarly, if PIP is
to output to the disk, the file name is indicated; if output is to
paper tape, no name is given. To call PIP; type:
.R PIP

9.2.2

Paper Tape to Disk Transfers

To move a paper tape to disk, strike the RETURN key when PIP
requests INPUT: Since PIP must output to the disk, respond to
OUTPUT: by typing a file name. When PIP requests OPTION: type T to
indicate that the paper tape is being loaded from the Terminal
reader. For example:
.R PIP
INPUT:

OUTPUT:FILEl
OPTIoNaT
The paper tape in the low-speed reader is read and stored in the
system as FILE1.
9.2.3

Disk to Paper Tape Transfers

To move a disk file onto paper tape, the use of file names is
reversed since PIP must input a disk file and output it to paper tape.
The option remains the same. For example:

.R PIP

INPUT'FILEl
OUTPUTa
OPTIONaT

9-19

The contents of FILEl are then punched at the Terminal.
9.2.4

High-Speed Reader/Punch Assignments

PIP can also be used with high-speed paper-tape devices. The
format of the INPUT: and OUTPUT: responses is the same. However,
for the high-speed reader, the option is R and for the punch it is P.
Since the reader and punch are assignable devices, they are not
always available (other users may have one "or both assigned). Therefore, whenever PIP is given a command which utilizes one of these
devices, it checks to make sure that the device is available. If it
is, PIP automatically assigns it (thus, it is not necessary to assign
the device before running PIP). If the device is unavailable, PIP
informs the user. For example:
INPUT:
OUTPUTtABCD
OPTIONaR
PIP reads the paper tape in the high-speed reader and stores it in
the system as ABCD.
INPUTsABCD
OUTPUT:
OPTIONCP
PIP punches out file ABCD on the high-speed punch.
INPUT:ABCD
OUTPUT:
OPTIONcP
DEVICE NOT AVAILABLE OR HUNG
The punch is assigned to another user, or there is no punch on the
EduSystem 50, or there is one but it is turned off.

9-20

9.2.5

Bin Format File Transfers
The examples above work for all ASCII file transfers (except

BASIC programs, explained in Section 9.4.8).

The examples are also

valid for punching BIN files, with one exception; most installations
do not allow any BIN format tapes to be loaded from the low-speed
reader.
9.2.6

Moving Disk Files
PIP can be used to move the contents of one file into another.

This is often useful in copying a file from another user's library
(providing the file is not protected) into your own library.

copy from disk file to disk file, specify a file name for both input
and output.

Reply to OPTION: by striking the RETURN key.

For

example:

INPUT:FOCAL 2
OUTPUT: FOCALX
OPTION:
PIP gets FOCAL from account· number 2's library and moves it into the
file FOCALX.
9.2.7

Deleting Disk Files
One of the principal reasons for punching files on paper tape is

to free disk space.

Once punched, the disk file is no longer needed.

PIP offers a convenient means of deleting files, the Delete option:

INPUT:ABCD
OUTPUT:
OPTIONtD
PIP deletes file ABCD, provided that the file is not protected against
being changed.

9-21

9.3.7

BASIC File Transfers
BASIC stores its programs in a unique file format.

Therefore,

it is not possible to load or punch BASIC files in the usual way.

provide a convenient means of handling BASIC programs, the B option
is available in PIP.

The B option is used for both reading and

punching BASIC programs.

The responses to INPUT: and OUTPUT: indicate

the direction of the transfer; the high-speed reader or punch is
always assumed for the B option.

(To read or punch tapes at low-

speed, use BASIC itself.)
PIP assumes that any BASIC tapes it loads are clean and errorfree.

Only tapes actually created by BASIC should be loaded with

PIP.

Tapes created off-line, and thus liable to contain errors,

should be loaded low-speed by BASIC itself with the TAPE command.
9.3.8

Save Format File Transfers
Another special file format is that of the SAVE files, those

programs directly executed by EduSystem 50.

(The Systems Library

Programs are examples of SAVE format files.)

PIP provides the S

option, to allow these files to be punched on paper tape.
format tapes make sense only to PIP and PUTR.

SAVE

They cannot be input

to any other Systems Programs."
The responses to INPUT: and OUTPUT: indicate the direction of
the transfer; the high-speed reader or punch is always assumed for
the S option.
NOTE
SAVE format
PIP detects
LOAD ERROR,
peating the

tapes include a checksum.
If
an incorrect read, it prints
and terminates the load, rerequest for input.

9-21.1

TABLE 9-1
PIP OPTION SUMMARY
Option

Explanation

Transfer a BASIC program file between the disk and the
high-speed reader or punch. The response to input
and output indicates the direction of the transfer.

Delete the file specified for input.

List a BASIC program on the -line printer.

Load a save format paper-tape from the terminal. This
option will not work on most TSS/8 installations.

Transfer an ASCII file from the disk to the line
printer.

Punch the contents of a disk file on the high-speed
punch.

Read a tape from the high-speed reader and store it
as a disk file.

Transfer a SAVE format file between the disk and the
high-speed reader or punch. The response to INPUT:
and OUTPUT: indicates the direction of the transfer.

Transfer a file between the disk and the terminal
reader or punch.
The response to INPUT: and OUTPUT:
indicates the direction of the transfer.

9.3

COPY PROGRAM
Many EduSystem 50 installations include one or more DECtapes.

For these installations, DEC tape provides a convenient and inexpensive means of file storage.

The COpy program is used to transfer

files between disk and DECtape.
9.3.1

Using and Calling COpy
COpy is the intermediary between disk and DECtape.

To write a

disk file out to DECtape, COpy inputs the file from the disk, then

9-22

outputs it to the DECtape. To bring a DEC tape file onto the disk,
COpy inputs from the DECtape, then outputs to the disk.
Files kept on DECtape have file names just as they do on the
disk.

To avoid confusion, the user must tell COpy where the file

is to be found.

If it is on DECtape, the DECtape designation and

the number of the DECtape unit must preface the file name.

The DEC-

tape number is always separated from the file name by a colon:

Thus

DI:FILEI means the file name FILEI on the DECtape which is currently
mounted on DECtape unit number one.

The number of available tape

units varies among installations.

The maximum is eight (numbered

0-7).

If a file name is not prefaced by a DECtape number, the file

is assumed to be on the system disk.
Files stored on DECtape do not have protection codes in the
sense that disk files do.
unauthorized access.

They are, however, protected against

When a DECtape is not mounted, it is not

available to any user.

When it is mounted, it is available only to

the user who has assigned the DECtape unit on which it is mounted.
Even then it can not be altered unless the DECtape unit is set to
WRITE ENABLE.

Users should be sure to assign a DECtape unit before

mounting their tape, and dismount the tape before releasing the device.

Normally, the DEC tape unit to be used should be assigned

before calling COpy.
To call COpy, type:

.R COpy

COpy responds by asking which option the user wishes to employ.
The COpy options are discussed below and summarized in Table 9-2.

~- 22.5

9.3.2

Loading Files from DECtape

To load a file onto the disk from DECtape, use the COPY option.
When COpy requests OPTION, respond with COPY, or C, or strike the
RETURN key (the COpy option is assumed). When COpy requests INPUT,
type the number of the DEC tape unit on which the file can be found
(DO, Dl, D2, D3, D4, D5, D6, or 07) followed by a colon and the
name of the file on the DECtape. When COpy requests OUTPUT, type
and enter the name to be given to the output file on the disk. COpy
then moves the DECtape file onto the disk.' (When using COPY, it is
not mandatory to insert a space between the device designator and the
device number.) For example:
OPTION" COpy
INPUT" D4:PQR
OUTPUT- PQR

If for any reason, COpy cannot find the DECtape file specified
for input (the specified DECtape is unavailable or nonexistent, or
the file name does not exist on that DECtape), COpy prints a ? and
repeats the request for input. If the disk file specified for output
already exists, COpy prints a ? and repeats the request for output.
COpy does not overwrite an existing file. For example:
OPTION- C
INPUT- D9:PQR
? INPUT- D4' PQRS
?INPUT- D4:PQR
OUTPUT" PQR

9.3.3

Saving Disk Files on DECtape

Saving a disk file on DECtape is very similar to loading one ..
The option is still COpy. For input, respond with the name of the
file on the disk. For output, type the DECtape unit number, colon,
and the name to be given to this file. For example:
9-23

OPTION- C
I NPUT- ABCD
OUTPUT- D4aABCD
If COpy cannot find the file on the disk, or if it is protected,
COPY prints a ? and repeats the request for input.

If COpy cannot

create the desired DEC tape file (the specified DECtape does not
exist or is unavailable, or it is not WRITE ENABLED, or a file by
that name already exists on the tape) COPY prints a ? and repeats
the request for output.
9.3.4

Listing Directories
COpy can be used to list the directory of a device.

To list a

directory, respond to OPTION by typing LIST, or just L.

COpy then

asks which device directory it is to list.

To list a DECtape

directory, respond with the device name (DO, ... ,D7).
it by a colon.

•R

Do not follow

For example:

COpy

OPTION- LIST
I NPUT- D1
1372. FREE BLOCKS
NAME
SIZE
BASIC .SAV 66

FACTAL.BAS

CONVER.BAC
PALD .SAV

6
32

DATE
9-MAR-70
2-MAR-70
l-MAR-70
31-MAR-70

The unit of DEC tape storage is the block, which is 128 (decimal)
words.

Because the unit of disk storage, the segment, is generally

256 words, a file occupies twice as many blocks of DECtape storage
as it did segments on the disk.

9-24

COpy can also be used to list the user1s disk directory.

Use

the LIST option, but respond to DEVICE by simply striking the RETURN

key.

The directory .listing is similar to the listing obtained by

running the CAT program.

9.3.5

Deleting Files
COpy can also be used to delete files, either on the disk or on

a selected DECtape.

To delete a file, respond to OPTION by typing

DELETE, or just D.

Respond to INPUT by typing the name of the file

to be deleted.

If the file is on a DECtape, preface the file name

with the DECtape unit number and a colon.

For example:

OPTION- DELETE
INPUT- D4tABCD

If COpy cannot find the file to be deleted, or having found it,
cannot delete it (it is a protected disk file or a DECtape file on a
unit which is not WRITE ENABLED), COpy prints a ? and repeats the
request for INPUT.

9.3.5.1

Deleting All Existing Files on a Device

COpy can be used to delete all existing files on a device.
so, respond to OPTION by typing ZERO, or just Z.
INPUT respond with the name of the device.
system disk.

To do

When COpy requests

COpy will not zero the

The ZERO option should also be used to format a blank

DECtape before attempting to copy any files onto it.
OPTION- ZERO
INPUT- D4

For example:

TABLE 9-2
COPY OPTION SUMMARY
Option

Abbreviation

COpy

Transfer a file between disk and DECtape.

DELETE

Delete a file.

EXIT

Exit to the Monitor.

LIST

List a directory.

ZERO

Delete all files.

Explanation

COpy cannot delete files from a DEC tape unless it is WRITE ENABLED.
It cannot delete disk files which are write protected.

9.3.6

Example of COpy Usage

.ASSIGN D 5
D 5 ASSIGNED
.R COpy
OPTION- ZERO
DEVICE- D5
OPTION- LIST
DEVICE- D5

1462. FREE BLOCKS

NAME

SIZE

DATE

OPTION- LIST
DEVICEDISK FILES FOR USER 54~40 ON
NAME
SIZE
SOLVE .BAS
1

PROT
12

TOTAL DISK SEGMENTS: 1

9-DEC-74.

DATE
9-DEC-74
-

-- ......

. -

OPTION- COpy
INPUT - SOLVE
OUTPUT- D5:S0LVE
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I NPUT- SOLVE

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NAME
SIZE
SOLVE .BAS
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DATE
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OPTION- LIST
DEVICEDISK FILES FOR USER 54,40 ON
SIZE

NAME

PROT

9-DEC-74.

DATE

TOTAL DISK SEGMENTS: 0
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DEVICEDISK FILES FOR USER 54,40 ON
NAME
ABCD

.BAS

SIZE
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PROT
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9-DEC-74.

DATE
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TOTAL DISK SEGMENTS: 1
OPTION- RENAME
I NPUT- ABCD
OUTPUT- FIE.BIN<17>
OPTION- LIST
DEVICEDISK FILES FOR USER 54,40 ON
NAME
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.BIN

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TOTAL DISK SEGMENTS:
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fBS

.RELEASE D 5

9-DEC-74.

DATE
9-DEC-74
9-27

CHAPTER 10
ADVANCED MONITOR COMMANDS

10.1

INTRODUCTION
The fundamental Monitor commands described previously are those

needed to utilize existing System Library Programs.

The EduSystem 50

Monitor also provides powerful commands for users who wish. to create
their own library programs.
To use the System Library Programs described previously, it was
not necessary to be familiar with the actual machine that runs them,
the PDP-8/E.

To create new library programs for EduSystem 50, this

is necessary because they are written in the PDP-8 assembly language.
The user codes his programs for a 4K PDP-8, subject to the timesharing conventions discussed in this section.

The programs are

created with EDIT, then assembled by PAL-D and loaded by LOADER.
Only at this point are the programs able to be run by EduSystem 50.
In the course of this program development, the same program exists
in many formats.
The source program is a disk file containing ASCII characters
in an Editor format.

PAL-D reads the file and translates it into a

second file, the assembled program in BIN format.

Neither of these

files is capable of being executed directly by EduSystem 50.

The

BIN format tape must be loaded into core by LOADER before it can
actually be executed.
At this point it is possible to save the program in a file format
that is directly executable by EduSystem 50.

Such a file, called a

SAVE format file, contains an image of the user's core area after the
program has been loaded by LOADER.
10-1

These SAVE format files differ

from all the files which are created by System Library Programs and
cannot be executed directly by EduSystem 50. Thus, it is not possible
to save a BASIC program {e.g., FILEI while running BASIC}, then return
to Monitor type R FILEI, and get meaningful results. The program in
FILEI must be executed under control of the BASIC language processor.
Only SAVE format files can be called into execution directly by the
R command.

{All System Library Programs are stored in SAVE format

and can be run with the R command.}
NOTE
In the following examples, Sn, Cn, and
Dn are used to stand for alphanumeric
strings {such as file names}, octal numbers, and decimal numbers, respectively.
A number of Monitor command conventions are available to make
the commands easier to use. First, more than one command may be
typed on a line.
(i).

Individual commands are separated by a semi-colon

Second, only enough characters of a command to uniquely specify

it need by typed.

Thus, DEPOSIT can be abbreviated DE or DEP .

• LOAD FILEIJDEP 20 7000JST 200
is exactly equivalent to:
.LOAD FILEl
.DEPOSIT 20 1000
.START 200
These conventions are available for the elementary Monitor commands as well.

They are, however, especially convenient for the

advanced commands.

10-2

10. 2

CO"NTROL OF USER PROGRAMS
Once a PAL-D program has been loaded by LOADER, several Monitor

co~mands

are available for controlling its execution.

These com-

mands are shown in Table 10-1.
It is possible to give these utility commands while a user program is running.

The CTRL/B character (tB) gets the attention of the

Monitor without stopping program execution.
command stops the program.)

(tB followed by the S

tB can be used together with the WHERE

command to follow program execution.

After executing these commands,

Monitor does not put the Terminal back into Monitor mode.
TABLE 10-1
MONITOR PROGRAM CONTROL COMMANDS
Explanation

Command
DEPOSIT Cl C2 ... Cn

Deposit the octal values C2 to Cn in the locations starting at Cl. DEPOSIT is used to
make small octal modifications to a user
program. No more than 10 (decimal) locations
can be modified by a single DEPOSIT
instruction.

EXAMINE Cl

Print the octal contents of location Cl.

EXAMINE Cl Dl

Print the contents of Dl locations starting
at Cl.

START

Restart execution of a user program where it
was interrupted (either by execution of an
HLT or by tBS typed at the keyboard). When
the START command is given, the program's
state is restored.

START Cl

Start execution of a user program at location
Cl. When a program is started, keyboard
input is no longer interpreted as commands
to Monitor.
Input characters are passed to
the running program. START Cl clears the
user's AC and link.

10-3

Table 10-1.

(Cont.)

Command
WHERE

10.3

Explanation
Print the present status of the user program.
The user's AC, PC, LINK and switch register
are printed. Also, any EAE registers which
are present are printed.

DEFINING DISK FILES
The Monitor allows the user to save core images of his program

on the disk for future use.

However, before saving such a core

image, the user must define a disk file in which to save it.
Disk files, like the user's core, are made up of l2-bit words.
Unlike the user's core, which is always 4K in size, a file can be
any size.

The unit of disk file storage is the segment; a segment is

256 (decimal) words long.

Files are at least one segment long when

created and grow by appending additional segments to the end of the
file.

In defining a file, the user first creates it, then extends

it to whatever length he needs.

To have a whole 4K image on a system

with a segment size of 256 (decimal) words, a 16 segment file is required.

If only part of the contents of the user's core is to be

saved, a correspondingly smaller file can be used.
A file can be created at any time.

However, to modify or re-

define it in any way, the file must be open.
open for a user simultaneously.

Up to four files can be

Opening a file connnects it to an

internal open file number (0, 1, 2, or 3).

Once a file is open, it

is referenced by this internal file number rather than by its file
name.

10-4

10.3.1

Creating a Disk File

- The CREATE command defines an area of disk space and associates
it with the name given in the

co~uand

line.

The file name can be one to six alphanumeric characters of which
the first must be a letter.

Creating a file deletes any existing

file of the same name, unless that file is write protected.
created, files are always one segment in size.

When

A new file is arbi-

trarily assigned a protection code of 12, meaning that other users
may access it but only the owner may change it.

Until it has been

written, the contents of a newly defined file are undefined.
10.3.2

Opening and Closing a File

To use a file, it must first be opened with the OPEN command.
A file can be opened on any of four internal file numbers:

0, 1,

2, or 3.

If a file

A user can have up to four files open at a time.

is open on an internal file number for which a file is already open,
that file is first closed.

For example:

.CREATE AS
.OPEN 1 AB

AB is now an open file and can be referenced as file 1.
An open file can be closed at any time by means of the CLOSE
command.

Once closed, a file cannot be accessed in any way until it

is reopened.
single

It is possible to close more than one file with a

co~~and.

For example:

.CLOSE 0 1 2 3

10-5

10.3.3

Extending, Reducing, and Renaming a Disk File

When created, a file is one segment long.
needed, the original file can be extended.

If a larger file is

For example, the

command:
.EXTEND Cl 01
extends the file presently open on internal file Cl by 01 segments.
Extending a file adds one or more segments to the end of that file.
The contents of the old part of the file are not changed.

Until

written, the contents of the newly added segments are unspecified.
An existing file may be reduced in size by means of the REDUCE command.

For example, the command:

.REDUCE Cl 01
reduces the file presently open on internal file Cl by 01 segments.
Reducing a file deletes the number of segments indicated from the
end of the file.
unchanged.

The contents of remaining segments of the file are

If a file is reduced to zero segments, or if 01 is greater

than the number of segments in the file, it is deleted entirely.

example of the creation and deletion of a 4K file:
.CREATE FOURK
.OPEN 3 FOURK
.EXTEND 3 15
.REDUCE 3 16
Existing opened files can be renamed.
its contents in any way.

Renaming a file does not change

For example, the command:

-RENAME Cl 81
renames as 81 the file open on internal file number Cl.

10-6

10.3.4

Protection Codes

The user can protect his files against unauthorized access.

can also specify the extent of access certain other users can have
to his files.

For example, a user's associates can be permitted to

look at the data of certain files but not permitted to alter that
data.
When it is created, a file is assigned a protection code of 12.
This protection code is defined below and can be changed
. ':, but only by the owner of that file.

For example, the command:

.PROTECT Cl C2
gives the protection code C2 to the file open on internal file number
Cl.
The protection code is actually a 5-bit mask.

Each bit specifies

a unique level of protection.

File protection masks

(C2) are assigned as follows:

Read protect against users whose project number differs
from owner's.

Write protect against users whose project number differs
from owner's.

Read protect against users whose project number is same
as owner's.

Write protect against users whose project number is
same as owner's.

Write protect against owner. To change the program
the owner must change the protect code.

10-7

Protection codes are determined as the unique sum of any of
the above codes.

Some of the more common protection codes are as

follows:
Command

Explanation

PROTECT 1 0

Allow other users to access the file and
change it.

PROTECT 1 12

Allow other users to access the file but
not change it.

PROTECT 1 17

Allow only the file owner to read· the file.
He can also change it.

PROTECT 1 37

Allow only the file owner to read the file.
He cannot, however, change it.
(To change
it, he must first change the protection.)

A user's project number is the first 2 digits of the 4-digit
account number.

The protection word contains a filename extension,

and has the following format:

4
FILENAME EXTENSION
I

UNUSED
I

PROTECTION CODE
I

The filename extension gives additional information about the
file, which is printed in some directory listings.

The filename

extension codes are:
0

blank

.ASC

ASCII files, such as PAL source.

.SAV

Save format files.

.BIN

Binary files; must be loaded with program
LOADER.

. BAS

BASIC source file.

.BAC

BASIC compiled program file.

.FCL

FOCAL file

10-8

.TMP

Temporary file.

. OAT

Basic data file.

.LST

Listing file.

= PAL

PAL source file ..

The protection word may be set by using PROTECT:
.PROTECT 0 0217

This changes the protection of the file open under internal file
number 0 so that the file has an extension of .ASC, and that it
cannot be read or written by any person other than its owner.
Finally, the user can ask what file is open on a given internal
file number by means of the F (File

informatio~ command.

For exam-

ple, the command:
.F Cl

prints the following information about the file presently open on an
internal file Cl:
a.

Account number of file owner.

Name of file.

File extension.

Protection code.

Size of file in segments (decimal).

For example:

•F 1

0002 TYPE 01 12 5

10-9

10.3.5

Error Conditions

There are a number of error conditions which prevent the execution of the file definition commands (as previously described).

One

of the following error messages is printed by Monitor if an error
condition is detected:
Message

Explanation

DIRECTORY FULL

A CREATE command has been issued, but
the user's directory is full. He can
delete any of his files to make room
for the new file. This message also
indicates a user has exceeded his disk
quota.

[MYFILE EXCEEDING DISK QUOTA]

The user has extended a file beyond his
allowed disk quota. The amount of extra
space (grace) the user is allowed is
determined by the system manager.

FAILED BY n SEGMENTS

The user has attempted to extend a file,
but cannot because of lack of segments
on the system, or because he is attempting to go beyond the grace quota. The
number of segments requested, but not
available, is printed.

FILE IN USE

An EXTEND, REDUCE, PROTECT, or RENAME
command has been issued for a file which
is in use elsewhere by another user.
Because changing a file which is being
used (i.e., has been opened) could disrupt another user's work, under these
conditions such a change is prohibited.

FILE NOT FOUND

The user has attempted to OPEN a nonexistent file.

FILE NOT OPEN

An EXTEND, REDUCE, PROTECT, or RENAME
command has been issued for an internal
file number for which no file is open.

PROTECTION VIOLATION

An attempt has been made to change a
file which is write protected against
the user.

10.4. SAVING AND RESTORING USER PROGRAMS
Once a file has been defined, the user can save all or any part
of his user core in the file.

Files and user core are addresses in
10-10

the same way, by l2-bit words.
any part of core.

The user can transfer his file into

The SAVE command requires one to five parameters.
of the file to be written into must always be given.

The name
If the file

is not in the user's own library, the appropriate account number is
entered before the file name.

(Writing into a file owned by another

user is subject to file protection.)
are separated by spacess

In either case, the parameters

The SAVE command writes the indicated

section of core out into the indicated file.
If no parameters follow the file name, Monitor starts at location
zero of the user's core and saves it in location zero of the disk
file.

It continues to write core locations into the disk file until:

(a) it has written the whole 4K or (b) it has filled the file.

Either

condition completes the SAVE.
The user can further define his SAVE command by indicating parts
of core to be saved in specific parts of the disk file.

He does

this by typing one to three parameters following the file name.

The

first parameter following the file name indicates a specific disk file
address at which to begin writing.

The second parameter following the

file name indicates a specific core address at which to begin the
transfer.

If only the first two parameters are typed, the transfer

terminates when either the end of core or the end of file is reached.
Explanation

Command
SAVE Sl
SAVE Cl Sl

Assuming that a disk file Sl exists, and
that it is not write protected, the contents
of core are saved in Sl.
In the first case,
Sl is assumed to be in the library of the
user giving the command.
In the second
case, it is assumed to be in the library of
the user whose account number is Cl.

SAVE Sl C2 C3 C4

Locations C3 to C4 (inclusive) are saved in
file Sl starting at disk file location C2.
Sl is assumed to be in the user's own library.
If Sl is preceded by the parameter
CI, it is assumed to be in the library of
the user whose account number is Cl.

10-11

Once a core image has been saved in a disk file, it can be
restored to core by means of the LOAD command.

It should be noted

that the Monitor command LOAD is very different from the System
Library Program LOADER.

LOADER loads a BIN format file (created by

PAL-D) into the user's core.

LOAD loads a SAVE format file (created

by a previous SAVE command) into core.
The LOAD command requires from one to five parameters.
name of the file to be loaded must always be given.

The

If the file is

in the user's own library, this file name is typed after the SAVE
command itself.

If it is in another user's library, his account

number is entered before the file name.
is subject to file protection.)

(Reading another user's file

In either case, the parameters are

separated by spaces.
Explanation

Command

LOAD Sl
LOAD Cl Sl

Assuming that a disk file Sl exists, and
that it is not read protected, the contents
of the file Sl are loaded into core.
In
the first case Sl is assumed to be in the
library of the user giving the command.
In
the second case, it is assumed to be in the
library of the user whose account number
is Dl.

The user can further define his LOAD command by using the same
optional parameters discussed in the section on the SAVE command.
Explanation

Command
LOAD 81 C2 C3 C4

Locations C3 to C4 (inclusive) are loaded
from the file Sl starting at file location
C2.

LOAD NE~~ 5 10 17

Words 5 to 14 (inclusive) of the file named
NEWF are loaded into locations 10 to 17 of
the user's core.

10-12

It is not necessary to open a file before using it in a LOAD or
SAVE command.

Both commands automatically open the specified file
nurr~er

on internal file

3 before performing the transfer.

After

completion of the command, the file remains open on file number 3.
A special macro-command, RUN, exists to allow a program to be
loaded and started all in one command.
Command

Explanation

RUN Sl
RUN Cl Sl

Load file Sl into core from the disk and
start execution at location O.
In the first example, file Sl is assumed
to be in the user1s own library.
In the
second, it is assumed to be in the library
of the user whose account number is Cl.
RUN Sl is exactly equivalent to LOAD Sl:
START O. RUN Cl Sl is exactly equivalent to
LOAD Cl Sl: START O.

RUN Sl C2
RUN C1 81 C2

Load file into core from the disk and start
execution at location C2.

The R command (see the section EduSystem 50 Monitor)
case of the RUN command.

is a special

For example, the command:

.R Sl
loads file Sl from the System Library (account number 2) and starts
at location O.

R Sl is exactly equivalent to RUN 2 Sl.

Typing an address after the program name in a "R" or
"RUN" command causes execution to begin at that address,
rather than at zero.

10-13

Sometimes, when typing a complex SI command, the rubout (or delete)
key may have been used a number of times to make corrections, and the
user may not be quite sure of what was typed.

A LINE FEED may be

typed to instruct SI to print out the command line as SI currently
understands it.

If the command line was entered while a program was

running by prefacing the command with fB, SI will print tB to signify
this, or else it will start the line with a dot.

Similarly, if an

attempt is made to rubout characters when there are none to rubout,
SI will print either tB or a dot to signify this condition.
At times, the system becomes very busy, and an SI command takes
a long time to execute.

If a user attempts to enter another command

at this time, his typing is ignored and his terminal bell rings to
warn him to wait.
10.5

UTILITY COMMANDS
The Monitor provides a number of special purpose commands to aid

in program development and use.

The Monitor utility commands are

summarized in Table 10-2.

10-14

TABLE 10-2

MONITOR UTILITY CO~ll~NDS
Command

Explanation

BREAK

Print the current value of the user's
delimiter mask.

BREAK Cl

Set the user's delimiter mask to Cl.
(The
use of the delimiter mask is discussed in
the chapter on assembly language
programming).

DUPLEX

Place the user's terminal in duplex mode.
All characters typed at the keyboard are
automatically printed as they are entered.

RESTART

Print the user's restart address.

RESTART Cl

Set the user program restart address to Cl.
If CTRL/C is typed at the keyboard, Monitor
forces a jump to location Cl in the user's
program.

SWITCH

Print the current value of the user's switch
register.

SWITCH Cl

Set the user's switch register to Cl.
Monitor maintains a switch register for each
user.
When his program executes on OSR
(OR the switch register into the AC) this
value is the one which is loaded.

UNDUPLEX

Take the user's terminal out of duplex mode.
Input characters are received by the Monitor
and-by the user program without their being
printed at the console.

USER

Print the user's job number, account number,
and console number.

USER Cl

Print the job number, account number,
and console number associated with job Cl.

VERSION

Print the version of the Monitor being used.

10-15

CHAPTER 11

WRITING ASSEMBLY LANGUAGE PROGRAMS

11.1

INTRODUCTION
In addition to the higher-level programming languages available

in the EduSystem 50 library, the user can also code and run programs written in the PDP-8 assembly language, PAL-D (Program
Assembly Language).

These programs are prepared with EDIT, assembled

with PAL-D, then loaded with LOADER.
A user can program EduSystem 50 just as he would any other
4K PDP-8.

(Assembly language programs must fit in 4K of core.)

All memory reference instructions (AND, TAD, ISZ, DCA, JMS,
and JMP) function as on a stand-alone PDP-8.

All operate instructions

(instruction code 7) also function as on a regular PDP-8 (except that
microcoding HLT or OSR with any other operate instruction but CLA
gives unpredictable results).
The major difference between EduSystem 50 programming and
regular PDP-8 programming is in the lOT (input/output transfer)
instructions.

Some

instructi~ns

which are valid on stand-alone

PDP-8s, such as CDF, CIF, ION, IOF are considered illegal instructions under timesharing.

There are a great many new lOTs within

EduSystem 50 that are not valid on a regular PDP-8.

Finally, there

are lOTs which operate on EduSystem 50 in the same manner as on standalong PDP-8s.

(Table 7-2

is a summary of EduSystem 50 lOT

Instructions. )
The way EduSystem 50 actually executes an lOT instruction is
also different.

Non-lOT instructions (except HLT and OSR) are

executed by the hardware, while lOTs (and HLT and OSR) are executed
by the EduSystem 50 Monitor.
11-1

In general, EduSystem 50 provides the programming capabilities
of a 4K PDP-8 and allows programs of considerably greater complexity
to be run within the constraints of each user's 4K of core.

System

Library Programs, all of which were written in assembly language and
make use of the EduSystem 50 lOTs dealt with below, are examples of
programs which can be run on EduSystem 50.
NOTE: Some of the following instructions do not operate the same
under account 1. For information on these instructions, see the
Manager's guide.
11.2

CONSOLE I/O
User programs handle console (terminal) I/O in almost the same

way as stand-alone PDP-8 programs.

The KRB instruction is used to

input a character, the TLS instruction to output a character.

The

KSF and TSF (followed by JMP .-1) can be used but are not needed.
Monitor handles all timing problems whether these skip lOTs are
present or not.
EduSystem 50 differs from the stand-alone PDP-8 in that under
EduSystem 50 the user program interacts with multi-character input
and output buffers (maintained by Monitor) rather than with single
character registers.

Depending on the state of the system, these

buffers may have one, many, or no characters in them.

During

normal program execution, this fact is of no consequence.

User

programs still send and receive characters one at a time.

There are

times, however, when it is useful to clear out any and all characters
in the buffers; a special lOT exists for this purpose (SBC).
On a stand-alone system, characters are input as soon as they
are typed, whether they are of immediate interest or not.

Usually,

these characters are stored by the program until a terminating (or
delimiting) character is found.
characters is processed.

At this time, the whole line of

On a swapping, time-sharing system such as

EduSystem 50, this mode of operation is wasteful.

It is far more

efficient to allow input characters to accumulate in the Monitor
input buffer until a delimiter is found.

There is an lOT to specify

which characters are to be considered delimiters (KSB).
11-2

EduSystem 50 also allows programs to input and output strings of
characters.

The read string (KSR) and send string (SAS) instruc-

tions provide a convenient and efficient means of doing lengthy
transfers.
All keyboard input uses full-duplexed hardware; there is no
wired connection between the keyboard and printer (i.e., characters
are not printed on the console as typed).

Input characters are

echoed to the console under program control rather than by hardware.

Because input characters are allowed to accumulate .in buffers

before being passed to the user program, it is important to have
Monitor perform the echoing rather than user programs.

There is

an lOT (DUP) to set up this automatic echoing as well as an lOT
(UND) to inhibit echoing for such operations as reading tapes.
Read Keyboard Buffer (KRB)
Operation:

Octal Code:

Read the next input character into bits 4-11 of the AC.

Load Teleprinter Sequence (TLS)
Operation:

6036

Octal Code:

6046

The ASCII character in AC bits 4-11 is printed on the

user's console.
Skip on Keyboard Flag (KSF)
Operation:

Octal Code:

6031

The next instruction is skipped if there is a delimiter

character in the user's input buffer.
Read Keyboard String (KSR)
Operation:

Octal Code:

6030

Execution of this instruction initiates a transfer of one

or more characters from the user's keyboard to a designated core
area.

Before executing KSR, load the AC with the address of a

two-word block, where:
Word 1:

negative of the number of characters to be transferred.

11-3

Word 2:

address of the core area into which characters are to
be placed minus one.

The transfer is terminated when either:
a.

the indicated number of characters have been input or

a delimiter is seen.

At the end of the transfer, the word

count and core address are updated and the AC is cleared.
Send A String (SAS)
Operation:

Octal Code:

Before executing an SAS

6040

load the AC with the ·address

of a two-word block, where:
Word 1:

contains the negative of the number of characters to
be sent.

Word 2:

contains the address - 1 of the first word of the string.

The characters are stored one per word right justified starting at
the address specified by word 2.

Upon e'xecution of SAS, the system

takes only as many characters as will fit in the output buffer.

then makes the appropriate adjustment to word 2 to indicate a new
starting address and to word 1 to indicate the reduced character
count; it returns to the instruction following the SASe

If the char-

acter count is reduced to zero, the instruction following SAS is
skipped.

The instruction following the SAS usually contains a JMP

.-2 to continue the block transfer of terminal characters.

The

AC is cleared by SASe
Octal Code:

Set Keyboard Break (KSB)
Operation:

6400

Rather than activate a user's program to receive each

character as it is typed, EduSystem 50 accumulates input characters
until a certain character, or characters, is seen.

To tell the

Monitor which characters to look for (these characters are referred
to as delimiters), load the AC with a l2-bit mask before executing
a KSB.

For each bit in the mask which is set, Monitor considers

the corresponding character or characters to be delimiters.

11-4

Bit

Specifies

0 = check rest of mask
1

= any character is break

301-332 (all letters)

260-271 (all numbers)

211

(Horizontal tab)

212=215 (line feed, vertical

4- ... 1-

l..a..LI ,

241-273 ( ! " # $ %&' () *+ , - • /: ; )

240

274-300 «

333-337

([,It--)

377

(RUBOUT)

375

(ALT MODE)

any characters not mentioned above

RETURN)

(space)
+>?@)

Duplex (DUP)
Operation:

form

Octal Code:

6402

DUP informs Monitor that the user wishes each character

typed at the console to be echoed on that console's printer as it is
received by Monitor.

The DUP instruction does not affect the user's

registers.
Unduplex (UND)
Operation:

Octal Code:

6403

UND informs Monitor that the user wishes to suppress

character echoing.

This can be done for reasons of privacy or be-

cause a program does its own character echoing.

The user's registers

are unaffected by UND.
Octal Code:

Set Buffer Control (SBC)
Operation:

6401

SBC permits the user program to clear its terminal input

and/or output buffer.

Before executing SBC set bits 0 and 1 of the

AC as indicated below:
Bit 0

Clear output buffer.

Bit 1

Clear input buffer.

11-5

11.3

FILES AND DISK I/O
All user programs can gain access to disk storage.

The time-

sharing Monitor maintains a pool of available disk space which is
allocated in units referred to as segments.
each.

Segments are 256 word

These segments are used to make up user files on the disk.

Monitor also maintains, for each user, a directory of all files which
he has defined.
The lOTs which allow the user to access the disk are of two
types:

those which define files on the disk and those which transfer

data between a defined file and the user's core.
NOTE
CREATE and OPEN require that a user set up a file
name in core.
core.

FINF and WHO return file names to

Each must be specified in internal code

(excess 40 code) as shown in Table 11-1.

Charac-

ters are packed two to a word.
The first step in defining a file is to create it.

Creating a

file reserves a single segment of disk storage and associates it with
a name.

This file can then be extended to any length desired.

tending a file appends more segments to it.

Ex-

Similarly, a file can be

reduced by any number of segments.

Reducing a file removes the last

segment or segments from the file.

Reducing a file to zero segments

deletes it entirely.

Once created, a file can be protected, thereby

restricting access to it.

When created, a file can be read by any

user, but only the creator can write in it.
reset if desired.

This protection can be

Finally, it is possible to rename an existing file.

11-6

TABLE 11-1

EDUSYSTEM 50 INTERNAL CHARACTER SET
6-Bit 1
Octal

8-Bit
Octal

0
1

00
01
02
03
04
05
06
07
10
11
12
13
14
15
16
17
20
21

3
4
5
6
7
8
9

23
24
25
26
27
30
31
32
33
34
35
36
37

240
241
242
243
244
245
246
247
250
251
252
253
254
255
256
257
260
261
262
263
264
265
266
267
270
271
272
273
274
275
276
277

Character
Space
!

"
#
$
%
&

(
)

<
=

>
?

Character
@

B
C
D
E
F
G

H
I

J
K
L
M
N

a
p

Q
R
S
T
U
V
W
X
y

[

f
t

6-Bit 1
Octal

8-Bit
Octal

40
41
42
43
44
45
46
47
50
51
52
53
54
55
56
57
60
61
62
63
64
65
66
67
70
71
72
73
74
75
76
77

300
301
302
303
304
305
306
307
310
311
312
313
314
315
317
317
320
321
322
323
324
325
326
327
330
331
332
333.
334
335
336
337

IThe 6-bit octal code is used to store passwords and file names only.

11-7

None of these actions affect the contents of the file-they only
reserve space on the disk.

Until it has been written in, the actual

content of a file is unspecified.

Extending a file does not alter the

content of the file as it previously existed.
be used to read and write data.

Once defined, files can

Any number of words (1 to 4096) can

be moved from any part of the user's core to any part of a file
(subject to file protection).
in core and a word count.

The user program specifies a location

This indicates how many words are to

be transferred and from (or to) where in core they are to be moved.
Also specified is a disk file address indicating what part of the file
is involved.

This address is the address of a word in the file.

Files are addressed in the same manner as core:

in 12-bit words.

Unlike core, however, files can be longer than 4K.

To address these

files provision is made for a 24-bit disk file address, containing
the high-order and low-order file addresses.
File addresses are independent of any consideration of segments.
The file address is meaningful only in defining files.

Files can be

read and written across segment boundaries without restriction.

(The

user cannot read or write beyond the last segment boundary.)
When it executes a file read or write rOT, the system updates the
core address and word count and places an error code in the error
word (see RFILE) if any error is detected.

At the end of a successful

transfer, the word count is set to zero and the core address set to
the last word transferred.

rf the transfer cannot be completed for

some reason, the word count and core address indicate how much of
the transfer was successful; the error word indicates the cause of
the failure.

All file operations except CREATE (and OPEN) require

that the file be open.

Up to four files can be open at a time.

The

process of opening a file associates it with one of four internal
file numbers (0, 1, 2 or 3).

All file rOTs except CREATE and OPEN,

are specified in terms of one of these internal file numbers, rather
than a file name.

rOTs operate on the file which is indicated by
11-8

that internal file number at the time.

It is therefore possible to

write file handling programs which are independent of the actual
file(s) they operate on.
Each user has a disk quota, defined by the system manager.
When a file is extended beyond this quota, the Monitor prints the
message [EXCEEDING DISK QUOTA].

When this happens, the user may no

longer create files and may only extend.

The amount by which a user

may exceed his disk quota is called the "grace" quota, and is defined
by the system manager.
File lOTs, that are successfully completed, return with the AC
cleared~

If an error was found which prohibited execution of the lOT,

one of the following error codes is returned.
Code
4000

There was no file opened on the specified internal file
number.

4400

Attempting to redefine a file which is open to another
user.

5000

Attempting to create a file for a user whose directory
is full, or who has exceeded his disk quota.

5400

Bad directory.

6000

File protection violation.

6400

Invalid file name.

7000

Attempting to open a nonexistent file.

7400

Disk is full.
Octal Code:

Create a File (CRF)

6610

Operation:

The user can request the system to create a new file of

one segment.

The user program provides the new name for the file.

Load the AC with the beginning address of a 3-word block: where:

Words 1 through 3:
contain the 6-character name.
If there is some reason why the request cannot be granted, the system
will return a non-zero error code in the AC. The protection code of
a newly created file is 12.
11-9

Extend A File (EXT)
Operation:

Octal Code:

6611

To extend the length of an existing file, that file must

be currently open.

Load the AC with the beginning address of a

2-word block, where:
Word 1:

contains the internal file number of the file to be
extended.

Word 2:

contains the number of segments the system should
append to the file.

If for some reason the request to extend a file cannot be ,granted,
the AC will contain 4000, 6000, or the number of segments it failed
to append.
Octal Code:

Reduce A File (RED)
Operation:

6612

To reduce the length of an existing file, that file must

be currently open.

Load the AC with the beginning address of a

2-word block, where:
Word 1:

contains the internal file number of the file to be
reduced.

Word 2:

contains the number of segments to be removed.

This request is granted unless the file to be reduced is currently
opened to another user or if the file is write protected against the
user.
Octal Code:

Rename A File (REN)
Operation:

REN is used to change the name of a file.

6600

Load the

AC with the address of a 4-word block where:
Word 1:

contains the internal file number associated with
the file whose name is to be changed.

Words 2-4:

contains the new name.

This name is in 6-bit

characters packed two in a word.

11-10

Protect A File (PROT)
Operation:

Octal Code:

6604

The owner of a file can protect his file from unauthor-

ized attempts to access i t by using this instruction.

Before ex-

ecuting PROT, load the AC with:
Bits

File extension code (for further information

to 4

on extensions see the description of the
PROTECT Monitor command).
Bits 5 and 6

Internal file number of the reserved file to be
protected.

Bit 7

Write protect against owner.

Bit 8

Write protect against users whose project
number is same as owner's.
Read protect against users whose project number

Bit 9

is same as owner's.
Bit 10

Write protect against users whose project number
differs from owner's.
Read protect against users whose project number

Bit 11

differs from owner's~
A file must be opened before it can be protected.

PROT is legal

only when performed by the file owner, i.e., the user who created
the file.

All attempts to access the file which violate any of the

protection flags are considered illegal.

(For further information

on project numbers, see Appendix C) .
Octal Code:

Open A File (OPEN)
Operation:

6601

OPEN is used to associate a file with an internal file

number, which is necessary because all file operations are in terms
of the internal file numbers.

Before executing the OPEN lOT, load

the AC with the beginning address of a 5-word block, where:
Word 1:

contains the internal file number.

Word 2:

contains the account number of the owner of the
file.

If 0, the account number of the current user

is specified.
11-11

Word 3-5:

contain the name of the file to be opened.

This

name is in 6-bit characters packed two to a word.
If there was another file associated with the internal file number
before the execution of the OPEN lOT, it is closed automatically
before the new file is associated with the internal file number.
Close A File (CLOS)
Operation:

Octal Code:

6602

CLOS terminates the association between files and their

internal file numbers.

Before executing CLOS, load the AC with a

selection pattern for the internal file numbers whose associated
files are to be closed.
I

The file is closed if bit I is 1, where

= bit 0, 1, 2, or 3.

READ File (RFlLE) and Write File (WFlLE)

Octal Code:
6603 & 6605

Operation:

Once the association of a file with an internal file num-

ber has been made, these lOTs allow the actual file reference to be
made.

They are illegal on a file that has not been opened (asso-

ciated with an internal file number).
To read or write a file, load the AC with the address of a 6-word
block, then execute the lOT.

The format for the 6-word block is:

Word 1:

contains the high-order file word address.

Word 2:

contains the internal file number

Word 3:

contains the negative of the number of words for the
operation.

This number is either the number of

words to be read or the number of words to be
written.
Word 4:

contains a pointer to the beginning address - 1 of a
buffer located in the user program.

On a read oper-

ation this buffer receives the information from the
file:

on a write operation this buffer holds the

information that is to be sent to the file.

11-12

Word 5:
Word 6 :

contains the least significant 12 bits of the initial
file word address to begin the operation.
contains an error code:
0 if no error
1 if parity error
2 if file shorter than word count
3 if file not open
if protection violated
4

The read or write begins at the word speci.fied by words 1 and 5.
For example:
TAD X

WFILE

.+1
~

-2~~

6477
2~~

means: write 200 (octal) words starting at word 200 of the file
that is associated with internal file number one from a core area
starting at location 6500.
After completion of the transfer, the word count (word 3) and core
address (word 4) are updated. If an error was detected the appropriate error code is placed in word 6.
Octal Code:

File Information (FINF)

Operation: FINF enables a user program to determine what file,
if any, is associated with an internal file number. Load the AC
with the beginning address of a 7-word block, where:
Word 1:

contains the internal file number for which the

Words 2

user program wishes information.
contain the information that the system returns

through 7:

after executing FINF.

11-13

6613

Word 2:

contains the account number of the owner or zero
if no file is associated with the internal file
number, that is, the file is not open.

Words 3-5:
Word 6:

contains the name of the file in 6-bit code.
contains the file extension code and protection
code. See Monitor PROTEC~ command for more details.

Word 7:

contains the number of segments which compose
the file.

11.4 'ASSIGNABLE DEVICES
Users can access both their own terminal and the disk; with the
remaining system devices (referred to as the assignable devices)
this is not true.

One function of the Monitor is to ensure that de-

vice usage never conflicts.

Only one user at a time can access the

high-speed paper-tape reader or punch, or anyone of the DECtapes.

To ensure that only one user can access a device, EduSystem

50 requires that the device be assigned before it is used.

After a

device is assigned, it is not available until it is released by its
owner.
Once assigned, the device is programmed
alone PDP-8.

much

as on a stand-

The RRB instruction is used to read a character from

the high-speed reader; the PLS instruction is used to punch one on
the high-speed punch.

The skip lOTs (RFS and PSF) can be used

(followed by JMP.-l) but are not necessary.
there are two string transfer commands:

For block transfers,

RRS and PST.

The DECtape instructions have been simplified.

A single instruc-

tion, DTXA, initiates the transfer of a block of data.

The DTRB

instruction is then used to determine if the transfer was successful.
The skip instruction, DTSF, can be used (followed by JMP.-1) but is
not necessary.

11-14

Executing any of the assingable device lOTs without first assigning the device gives the following results:

(a) If the device is

assigned to another user, the instruction is considered illeaal: nro.."

gram execution is now terminated and an error message printed~

•

,L--

(b)

If the device is available it is automatically assigned before execution of the lOT.

The device then belongs to this user until he

releases it.
Because these devices are shared by all users, the Monitor must
ensure that they are operable at all times.

In particular, the

Monitor must ensure that a user is not waiting for a device which is
not available.

This situation can arise when trying to use the punch

when it is turned off, or when the reader has read off the end of a
tape.

All these conditions, known as "hung devices"-are considered

to be system errors.

If the program doing the transfer has been en-

abled for system errors (by executing an SEA), control transfers to
the error routine indicated which must clear the error flag in the
status word before continuing (See Section 11.6).

If the user

program has not been enabled for system errors, a hung device causes
the program to be terminated and an error message is printed.
When the paper tape punch or line printer is off line or hung,
the Monitor takes special action so that it is usually possible to
continue with little or no data loss.
the output buffer is not cleared.

When these devices are hung,

A system error is generated, and

regenerated every few seconds until the condition is cleared.

the user program has not enabled errors, the result will be a printed
"HUNG DEVICE" message, and then the terminal bell will ring, trying

11-15

to persuade the user to do something. There are only two things the
user may do to remove himself from this condition. If he is not
interested in continuing, he may release the hung device. If he does
wish to continue he should put the device on line, and it should
take off. He may now type "START" to continue program execut~on.
octal COde: 6440

Assign Device (ASD)

Operation: If the device specified by the content of the AC is
available, it is assigned to the users program and the AC is cleared.
Otherwise, the number of the job owning the device is placed in
the AC. If the device does not exist, 7777 is returned in the AC.
4000
4001
4003
4004
4005+N
4015

Paper-tape reader
Paper-tape punch
Line printer
Card reader
DECtape unit N, N=0-7
RK8E drive N, N=0-3

The assignment is in effect until a corresponding REL instruction
or LOGOUT is executed.
Octal Code: 6442

Release Device (REL)

Operation: The device specified by the contents of the AC is releaseed (providing it was owned by the U5e= sxecuting the REL).
The AC is cleared. Releas ing a device makes it available to other
users.
Octal Code: 6011

Skip on Reader Flag (RSF)

Operation: The contents of the PC are incremented by one so that
the next sequential instruction is skipped.
octal Codes; 6012 & 6016

Read Reader Buffer (RRB)

Operation: The contents of the reader bu~fer are transferred into
bits 4 - 11 of the AC. This instruction does not clear the A2.
If the reader buffer is empty, the user program is put into a wait state
until the buffer is full or an end-of-tape condition is detected.

11-16

Reader Clear Buffer (RCB)

Octal Code: 6017

Operation: Any characters, which may have been read from the highspeed reader but not passed to the user, are cleared fro the
buffer.
Read Reader String (RRS)

Octal Code: 6010

Operation: This instruction initiates a transfer from the high-speed
reader to a selected area in the users core. Before executing RRS,
load the AC with the address of a 2-word block where:
word 1: minus the number of characters to be transferred.
word 2: the address of the user core area minus one.
The transfer is terminated by either of two conditions:

(a) the

word count (word 1) is zero indicating that the required number of
characters have been read or (b) the reader has read off the end of
the tape (a system error condition). In either case, the word count
and core address are updated. RRS clears the AC.
Load Punch Buffer Seguence (PLS)

Octal Code: 6026

Operation: The ASCII character in AC bits 4 - 11 is transmitted
to the high-speed punch. PLS does not clear the accumulator.
Skip on Punch Flag (PSF)

Octal Code: 6021

Operation: The contents of the PC are incremented by one so that
the next sequential instruction is skipped.
Punch String (PST)

OCtal Code: 6020

Operation: PST allows a user program to punch a string of charactses. Before executing PST, load the AC with the beginning address
of a 2-word block where:

11-16.5

Word 1:

contains the negative of the number of characters
to be punched.

word 2:

contains the beginning address - 1 of the string to
punched: the characters should be right justified
one per word.

After execution of PST, the system takes only as many characters as
fit in the punch buffer: it then makes the appropriate adjustment
to word 2 to indicate a new starting address and to word 1 to indicate the reduced character count.

It returns to the instruction

following the PST which may be a JMP .-2 to continue the transfer.
If the character count is reduced to zero, the instruction following
PST is skipped.

The AC is cleared by PST.
octal Code:

Line Printer Print (LPC)
Operation:

6666

The ASCII character in bits 4 through 11 of the AC are

placed into the line-printer buffer to be printed.

LPC does not

change the AC.
Octal Code:

Line Printer Skip on Flag (LSF)
Operation:

6661

The contents of the PC are incremented by one so that the

next sequential instruction is skipped.
Line Printer Send-A-String (LST)
Operation:
terse

Octal Code:

6660

LST allows the user program to print a string of charac-

Before executing LST, load the AC with the beginning address

of a 2-word block, where:
Word 1:

Contains the negative of the number of characters to
be printed.

Word 2:

contains the beginning address -1 of the string to
be printed: the characters should be right justified
one per word.

After execution of LST, the system takes only as many characters as
fit in the punch buffer: it then makes the appropriate adjustment to
word Z to indicate a new starting address and to word 2 to indicate

11-17

the reduced character count.

It returns to the instruction following

the PST which may be a JMP .-2 to continue the transfer.

If the

character count is reduced to zero, the instruction following PST
is skipped.

The AC is cleared by LST.

Load Status Register A (DTXA)
Operation:

Octal Code:

6764

DTXA allows a user program to read and write records

(l29-word blocks) on DECtape.

Load the AC with the beginning address

of a 3-word block, where:
Word 1:

contains:
Bit 1

Meaning

0-2

contains the transport unit select number,

is set to 1 to read/write in reverse

4-5

should be ¢

6-8=2
=4
9-11

for read data function,
"for write data function"
should be ¢

Word 2:

contains the DEC tape block number.

Word 3:

contains the beginning core address - 1 of a 2¢1 (octal)
word buffer.

After DTXA is given, the DECtape request is placed in the DECtape
request queue.

Control does not return to the user until the request

has been honored or an error has occurred.

DTXA does not update word

The AC is cleared by DTXA.

Skip on Flags (DTSF)
Operation:

Octal Code:

6771

The contents of the PC are incremented by one so that

the next sequential instruction is skipped.

11-18

Read status Register B (DTRB)
Operation~

the AC.

octal Code:

6772

The content of DECtape status register B is loaded into

This instruction is also used with the card reader and RK¢5.

See Read Status (RDS) for details=
Read card Alphanumeric RCRA)

Octal Code:

6632

Read card Binary (RCRB)

Octal Code:

6634

Read card Compressed (RCRC)

Octal Code:

6636

Before executing the above instructions, load the AC with the address
minus 2 of an 80 wo~d buffer. A card is read and the data is put
into the buffer in the same form as the corresponding hardware rOT.
The UUO returns in the AC the number of characters successfully
transferred to the user's buffer.

(See also 6772 - RDS.)
Octal Code:

Disk Load Address and go (DLAG)
Allows the user to read or write on the RK8E.

6743

To use, load the

AC with the address of a three word block, where
Word 1:

Bit 0 = 0 for a read,

= 1 for a write
Bits 3-8 contain the number of pages to read/write,
1 to 40.

Bits 9-10 contain the drive number 0 to 3.
Bit 11 contains the high order sector address.
Word 2:

contains the core buffer address minus one,

Word 3:

contains the low order sector address.

11-19

Upon return, the AC contains the number of blocks transferred.
To determine error conditions, see 6772-RDS.
The disk transfer is made in 400 (octal) word blocks.
drive contains 14540 (octal) blocks.

Each RK05

To specify the initial block

number, the high order bit goes into word 1 of the parameter block,
and the remaining 11 bits into word 3.

If the transfer requests an

odd number of pages on a write, the last page of the last block on
the disk will contain zeros.

Upon return, the AC contains (P+l)/2,

where P is the number of pages successfully transferred.
Octal Code:

Read Status (ROS)

6772

The contents of the device status register are placed into the AC.
The information obtained pertains to the RK8E, DECtape, or
Card Reader, depending on which was most recently used.
contents of the device status register are:
RK8E:

RK8E Status Register
Bit

Assignment

Control done

Heads in motion

Seek fail

File not ready

Busy error

Time out error

Write lock out error

CRC error

Data request late

10:

Drive status error

11:

Cylinder address error

11-20

The

DECtape:

TCOS/TCOI status register B

Bit 0:

Error flag

Mark track error

End of tape

Select error

Parity error

Timing error

11:

DEC tape flag (normal)

The status register for DECtape may also include 4¢¢¢ or 4¢¢1.
These are software generated errors such as block number out of range.
Card reader:

The device status register contains the address of the

last word of data transferred to the user's buffer.
the device status retister may contain 7777.

In addition,

This indicates that

CTRL/B followed by S was typed while a DECtape or RK¢5 transfer was
in progress, and the transfer was not finished.
lIeS

PROGRAM CONTROL

There are a number of ways that the status of a running program
can be changed. The program can be terminated in one of three ways:
by execution of a HLT, by the user typing CTRL/B followed by S to
force a program halt, or by a 'program error which forces Monitor to
terminate the program after printing an error message.
It is also possible for the status of a running program to change
without it being terminated. First, the user program can request
that it handle its own program error conditions. In this case, Monitor does not terminate a job on an error; instead, it transfers control to a user error handler. This error handler then determines
what the error was, by a CKS instruction and takes appropriate action.
Monitor also provides the program with an interrupt key, CTRL/C.
If the user types a CTRL/C, the Monitor unconditionally transfers
control to a restart address. Thus, the user program can handle
its own restarts.
11-21

Halt (HLT)
Operation:

Octal Code:

7402

This instruction is used to stop the user program and

return control to Monitor.

Executing HLT is equivalent to typing

tBS followed by RETURN.
Set Restart Address (SRA)
Operation:

Octal Code:

6417

This instruction allows the user to specify an address

to which control is transferred when an tc is typed on the user's
console.

Load the AC with the restart address and execute SRA.

If tc is detected, the program's input and output buffers are
cleared, the AC and Link are cleared and control goes to the restart address.
Set Error Address (SEA)
Operation:

Octal Code:

6431

This instruction allows the user to specify an address

to which control is transferred in the event of a system error.
the AC with an address before executing SEA.

Load

If a system error is

detected, Monitor simulates a JMS to the error address.

The pro-

gram counter is stored in the error address and control transferred
to the error address +1.

AC, Link, and input/output buffers are

not affected. The error code of the system error is in STRO bits
9-11. The error routine must read these bits (by a CKS) to determine
the cause of the error, then clear them by means of a CLS.
The only error code that occurs, for example, in the course of
normal system usage is due to a hung device.

This error occurs when

the user attempts to use a punch# line printer, or reader which is
not turned on, or allows the paper-tape reader to run off the end of
a tape.

In the case of the line printer or the punch, the error

routine must release the device or the device must be turned on to
clear the error condition.

The illegal rOT error probably means that

an assignable device lOT was executed without the device first being
assigned.

Swap and file errors occur if a hardware error is detec-

ted while Monitor is swapping user programs or while reading or writing

11-22

file directories.

These are system malfunctions from which there is

no recovery.

PROGRAM k~D SYSTEM STATUS

11.6

Because EduSystem 50 programs run under
sharing Monitor, it is important for them to determine their status
within the system and the status of the system as a whole.

Several

lOTs, listed below, have been defined for this purpose.

octal Code:

Check Status (CKS)

6200

Monitor maintains for each user a complete set of status information, his program's running status and the state of his input/output
devices.

This status information, stored in three words, can be

accessed by a running program with the CKS instruction.

Before

executing a CKS, load the accumulator (AC) with the address of
a three-word block.

Executing CKS stores the three status words

(STRO, STRl, and DEVICE STATUS REGISTER) in the three-work block
and clears the AC.
The formats of these registers are:
STRO Bits

Run Bit

User program is in the run state

Error Enable

Program handles its own errors

JCOMBD

Program was compute bound

JSPEEK

User has R privilege

JSACC

User is privileged account

JSIOT

System use only

JSIOTC

System use only

Not used

JSlNER

System use only

9-11

Error Code

System detected error condition
1
Illegal lOT
2
Swap read error
3
Swap w~ite error
5
D~sR f~l~ error
6
Hung dev~ce

11-23

STRl Bits
0

Timer

Time is up

File 0

Internal file 0 is not busy

File 1

Internal file 1 is not busy

File 2

Internal file 2 is not busy

File 3

Internal file 3 is not busy

Delimiter

Line Printer

There is a delimi ter in the input buffer
Output buffer is not full

Teleprinter

Output buffer is not full

Reader
Punch
Error

Character in reader buffer
Punch buffer is not full
System error has occurred.

wait

Job is not waiting

10
11

Device Status Register:

The contents of the Device Status Register

pertain to the card reader, DECtape, or RK¢5 as described under
the Read Status (RDS) lOT.
Octal Code:

OR with Switch Register (OSR)
Operation:

7404

The content of the user's switch register is inclusively

ORed into the AC.
Set Switch Register (SSW)

Octal Code:

6430

Operation:

The content of the AC is stored in the user's switch

The AC is cleared.

Assembly language programs run under control of the Monitor.
The following lOTs are defined to allow a program to determine the
status of the system as a whole.
Octal Code:

Segment Size (SIZE)
Operation:

6614

The segment is the basic unit of on-line file storage.

The size of a segment (0400 octal) is returned in the AC.

11-24

Segment Count (SEGS)
Operation:

Octal Code:

6406

The number of available disk segments is returned in

the ACe

Account (ACT)

Octal Code:

6617

Operation: The account number (of the job number in the AC) is returned in the AC. If AC is 0, the account number for the current
job is returned. If the requested job does not exist, zero is
returned.
Octal Code:

Who (WHO)

6616

Operation: The account number and password of the current job are
returned to the 3-word block whose address is in the AC and the AC
is cleared.
Octal Code:

User (USE)
Operation:

6421

Return in the AC the number of the current job.
Octal Code:

Console (CON)

6422

Operation: Return in the AC the console unit number assigned to the
job whose number is in the AC, if that console number does not exist,
-1 is returned.
Octal Code:

User Run Time (URT)

6411

Operation: Load the AC with the address of a 3-word block,
where word 1 contains the number of the job for which the run
time is sought. The run time is returned in the last two locations
of the block. If job 0 is specified, the run time of the current
job is returned. The AC is cleared.
Octal Code:

Time-of-Day (TOO)

6412

Operation: Returns the time of day in the two locations starting
at the location of the address in the AC. The time of day is
returned in clock ticks since midnight. The AC is cleared. The
clock ticks 10 times per second.

11-25

RETURN CLOCK Rate (RCR)
Operation:
AC.

Octal Code:

6413

The number of clock ticks per second is returned in the

The clock ticks every 100 ms, the AC will be set to 12 (octal).
Octal Code:

Date (DATE)
Operation:

Returns the date in the AC.

6414

The format of this·12-bit

number is:
DATE=«YEAR-1974)*12+(MONTH-l»*3l+DAY-l
Octal Code:

Skip on EduSystem 50 (TSS)
Operation:

6420

This instruction is used by programs which run under

both EduSystem 50 and on a standard PDP-B.

Under EduSystem 50,

the instruction following TSS is skipped and the Monitor version
number is returned in the AC.

On a standard PDP-B, the rOT has the

effect of a NOP instruction.
Quantum Synchronization (SYN)
Operation:

Octal Code:

6415

Upon execution of this instruction, the system dis-

misses the user program and sets it in the run state so that it will
be run again in turn.

Ordinarily, this instruction is used to en-

sure a full time quantum to perform some critical operation.
Set Time (STM)
Operation:
gram.

Octal Code:

6416

The system provides a clock time for each user pro-

By means of this rOT, the time can be set to "fire" after a

specified number of clock ticks have elapsed.
the time (in seconds) to prime the timer.

Load the AC with

Upon execution of the

STM instruction, the system sets the time to "fire" in the specified
number of seconds, clears the AC, and dismisses the job. After the
specified time has elapsed, the job is restarted.

Due to the time-

sharing environment, this time may vary by a second or two.

11-26

.1..1. • 0

.1./ L.

SPECIAL INSTRUCTIONS

The following instructions are usable only on certain TSS/8
systems, and are not included in the PALD symbol table.

Grt Flags (GTF)

Octal Code: 6004

Operation: Upon execution of this instruction, the link is
placed into AC bit 0, and the EAE GT flag (if present) is placed
into AC bit 1. The rest of the AC is cleared. This instruction
is valid only on a PDP-8/E.
Restore Flags(RTF)

Octal Code: 6005

Operation: Upon execution of this instruction, AC bit 0 is
placed into the link and AC bit 1 is used to set or clear the EAE
GT flag (if present). The AC is not changed by RTF. This instuction
is valid only on a PDP-8/E.
Skip or Greater Than ~,~g5aJ SGT)

Octal Code:

6006

Operation: If the system includes an EAE, and if its GT flag
is set, this instruction will cause the PC to be incremented by one
so that the next core location is skipped. This instruction is
valid only on a PDP-8/E.

In addition, all operate type instructions which the computer is
capable of executing may be used. This includes the BSW and MQ
instructions on any PDP-8/E, and all the EAE instructions on systems
which have an EAE.

11-27

11.7

PDP-B COMPATABILITY

Programming EduSystem 50 in assembly language is very similar to
programming a stand-alone PDP-B.

All instructions except the lOTs

operate identically in either case.

As discussed previously, pro-

gramming such devices as the terminal and high-speed reader/punch for
EduSystem 50 is somewhat simpler.
include timing loops.

EduSystem 50 runs programs which

Thus, programs written for stand-alone PDP-Bs

with terminal and high-speed reader or punch will run on EduSystem
50, although generally not as efficiently as programs which are
written specifically for EduSystem 50.
The same is not true for disk and DECtape operations because
EduSystem 50 uses a simplified programming structure for these
devices.

The actual differences in coding are very small.

It is a

simple task to adapt previously written code for EduSystem 50 disk
and DECtape.
There are a few standard changes which users generally make
in adapting PDP-8 code to EduSystem 50.
rather than the user program.

Monitor does the echoing

The TLS which does the echo can be

deleted and a DUP instruction added somewhere near the start of the
program.

Also, for efficiency, the EduSystem 50 delimiter capa-

bility can be used.

A KSB in the program determines what the

delimiters are.
Many PDP-B programs execute a reader and punch lOT early in the
program, to initialize the device, whether they are actually to be
used or not.

If the devices are free, they are assigned and thus

made unavailable to other users.
terminates on an illegal lOT.
these lOTs randomly.

If they are unavailable, the progra~m

Thus, it is important not to execute

If a disk card reader or DECtape is involved,

11-28

the actual transfer code must be altered to conform to EduSystem 50.
(The fact that core page 37, locations 7600 through 7777, is available to EduSystem 50 programs is useful in making these changes.
New code can be placed in the area normally reserved for the Binary
Loader.)
The most difficult code to convert is that code which operates
under interrupt.

To be run under EduSystem 50, these programs must

be recoded so as not to use the interrupt.
lOTs for nonexistent devices are ignored as are CDFs and CIFs.
It must be remembered that many lOTs have been redefined for use as
special EduSystem 50 instructions.

In all other situations, EduSystem

50 remains compatible with stand-alone systems whenever possible.

11-29

APPENDIX A
EDUSYSTEM 50
MONITOR COMMAND SUMMARY
A.I

MONITOR CO~P~DS

A Monitor command is a string of characters terminated by a
semicolon (i), a colon (:), or a carriage ~eturn (RETURN key).
Parameters of commands can be octal n~~hers, decimal n~~bers,
character strings, or single letters. In the following summary,
parameters are coded as follows:
Cl, C2, •••
01, 02, •.•
LI, L2, •••
Sl, S2, •••
A.l.l

represent octal numbers
represent decimal numbers
represent single letters
represent character strings

LOGGING IN AND OUT
KJOB
LOGIN Cl Sl

LOGOUT
TIME Cl

used as an alternative to LOGOUT
Request to login:
Cl = user's account number
Sl = user's password
Request to logout: processing and device
time are ~rinted.
Cl = job number
A)

If Cl is omitted and the user is
logged in, the processing time of
the current job is printed. If
Cl=O, or if the user is not logged
in and Cl is omitted, the time of day
is printed.

A-I

A.l.2

DEVICE ALLOCATION
ASSIGN D Cl

Reserve DECtape unit:

ASSIGN K Cl

Assigns a specific RK,05 unit

ASSIGN Ll

Reserve device:
Ll

Cl = DECtape unit number

= R for paper tape reader
p

for paper tape punch

D for any DECtape unit
L for line printer
C for Card Reader
K for any RK,05 unit
RELEASE D Cl

Release DECtape unit: Cl = DECtape unit number

RELEASE K Cl

Release an RK,05 unit:

RELEASE Ll

Release device:
Ll

= RK,05 drive number

= R for paper tape reader
p

for paper tape punch

L for line printer
C for card reader
A.l.3

FILE HANDLING
CLOSE Sl

Close files:
Sl = list of internal file numbers

CREATE 81

Create new file:
Sl = name of new file

EXTEND Cl Dl

Extend length of file:
Cl

= internal file number

Dl = number of segments to be added to
end of file
F C,l

Print information about an open file
Cl = internal file number

A-2

OPEN C1 81 C2

Establish association between internal file
number and file:
Cl = internal file nurnher
Sl = file name
C2 = account number.
If omitted, the user's
account is assumed.

PROTECT C1 C2

Protect a file:
C1 = internal file number
C2 = new file protection mask (See 10.3.4)

REDUCE C1 D1

Reduce length of file:
C1 = internal file number
D1 = number of segments to be removed from
end of file

RENAME C1 Sl

Rename a file:
C1 = internal file number
Sl = new name of file

A.1.4

CONTROL OF USER PROGRAMS
DEPOSIT C1 C2 ••. Cn Store in core memory:
C1 = location
C2 = contents to be stored in location C1
C3 = contents to be stored in location C1+1, etc.
EXAMINE C1 D1

List specified contents:
C1 = first location
Dl = number of location to be listed, D1<10
(decimal)

RESTART

Print the program restart address

A-3

RESTART Cl

Set program restart address.

START

Restart user program.

START Cl

Execute user program:
Cl = starting location

A.l.S.

UTILITY COMMANDS

BREAK

Print keyboard break mask.

BREAK Cl

Set keyboard break mask:
Cl = new mask

DUPLEX

Echo typed characters on printer.

LOAD Cl Sl

Load Core image:

LOAD Cl Sl C2

Cl = owner's account number~ if not specified
the user's account is assumed.

LOAD Cl Sl C2 C3

C2 = file address of first word to be loaded: if
not specified, ~ is assumed.

LOAD Sl

C3 = core address of first word to be loaded: if
not specified~ ~ is assumed.

LOAD Sl C2

= core address of last word to be loaded~ if
not specified, highest possible value is
assumed.

LOAD Sl C2 C3
LOAD Sl C2 C3 C4
R Sl

Run system file:

R Sl Cl

Sl = name of file
Cl = beginning address: if omitted,

is assumed.

RUN

Run user file:

RUN

Cl Sl

Sl = name of file

RUN

Sl C2

Cl = owner's account number: if omitted, the user's
account is assumed.

RUN

Cl Sl C2

= starting address: if omitted, ~ is assumed.

stop execution
Save Core image:

A-4

SAVE Cl Sl

Cl = owner's account number; if not specified the
user's account number is assumed.

SAVE ...... ..1.. 81

81 ~ name

SAVE Cl Sl C2 C3

SWITCH

Print the current value of the user's switch
register.

,.."

file address of first word to be saved; if
not specified, ¢ is assumed.

Set switch register:
SWITCH Cl

Cl = word to be set

TALK Cl Sl

Send a message to console Cl:
Cl

= destination console

Sl = message
UNDUPLEX

Inhibit echo of characters typed to a user program

USER

Print the user's job number, account number, and
console number.

USER Cl

Print the job number, account number, and console
number of job Cl.

WHERE

Print the current value of the user's PC, AC,
link, swi t·ch register, and EAE registers.

A-5

APPENDIX B
CHARACTER CODES
The ASCII l character codes shown in the following table are
used by EduSystems as the argument in the CHR$ function.

For

each ASCII code a second acceptable form is permitted In eHR$.
The second code is obtained by adding 128 to the code given in
the following table.

For example, CHR$ would print A in response

to either 65 or 193 as an argument.

These codes are also used with

the CHANGE statement in EduSystem 50.

Character

ASCII Code No.
(Decimal)

linefeed

formfeed

RETURN

space

#
$

Character

ASCII Code No.
(Decimal)

IAn abbreviation for American Standard Code for Information Interchange.

B-1

Character

ASCII Code No.
(Decimal)

Character

ASCII Code No.
(Decimal)

1
2

49
50

54
55

8
9

56
57

88
89

[

]

B-2

APPENDIX C
STO~~GE

C.l

F~LOCATION

STORAGE MAP
The system:s storage allocation is illustrated below.

CORE MEMORY

DISK STORAGE

1 ' 4 - - - - - - M O N ITOR -------II~+I.----SWAPPING AREA -----t~-

Figure C-l.
C.2

EduSystem 50 Storage Map

FILE DIRECTORIES
There are two directories on the disk:

the Master File Directory

(MFD) referenced mainly by the system, and the User File Directory
(UFD), referenced by the user.
service the UFD.

One of the functions of the MFD is to

A UFD is a particular user's file directory con-

taining the names of programs he has created on the disk.
The UFD is a file like any other file except that its filename is
the project-programmer number and password.

When a user is logged in

under a specific number and references the disk, he is actually referencing his own file area on the disk through the UFD which has his
project-programmer number as its name.

C-l

MASTER FilE DIRECTORY
WORD 1

PROG. NO.

PROJECT NO.

USER FilE DIRECTORY
(1

CHAR)

FilE

(1 CHAR)

NA ME

(1 CHAR)

WO RD

(1 CHAR.)

PA SS

(1 CHAR.)

WO RD

(1 CHAR.)

LINK TO NEXT ENTRY

LINK TO NEXT ENTRY
EXT

IDISK QuOTJ'\

I"" PROTECTED BITS

CONSOLE TIME

SEGMENT COUNT

CPU TIME

DATE OF CREATION

POINTER TO RETRIEVAL

"- LINK TO NEXT RETRIEVAL BLOCK

SEGMENT

Figure C -2.

File Directories

System account numbers are a combination of a project number
and a programmer number. If expressed as a four-digit octal number,
the first two digits of the account number are the project number,
and the last two digits are the programmer number.

C-2

APPENDIX D
ERROR MESSAGES

program

Explanation

ABORT

BASIC

BASIC can not run for some
reason. perhaps the user's
disk quota is exceeded.

ARRAY OR RECORD USED BEFORE
DEFINITION

BASIC

The RECORD statement must occur

Message

before any reference to it is
made.

A DIM statement must occur

before an array is used.

(RECORD

and DIM are placed at the beginning of a program.)

BAD FILE FORMAT

BASIC

The program specified in response
to OLD PROGRAM NAME was not acceptable to BASIC.

This is gen-

erally caused by:

(1) trying

to load an obsolete compiled
(.BAC) file, or (2) trying to
load a non-BASIC (FORTRAN or PAL-D)
program.

BAD FILE NAME

BASIC

The file name used is not valid;
e.g., it does not begin with a
letter.

The argument of the SLEEP state-

BAD SLEEP ARGUMENT

ment must have a number greater
than or equal to 0, and less
D-l

than or equal to 4095.

Message

Program

Explanation
While performing CHANGE A TO A$,

BAD VALUE IN CHANGE STATEMENT

one of the elements of the array
A was found to contain an illegal
value.

An OPEN statement tried to create

CAN'T CREATE FILE

a file, but there is:

(a) no

disk space available,

(b) no file

name specified, or (c) a null
string has been given as the file
name.

UNSAVE cannot delete a file.

CAN'T DELETE FILE

This

is usually due to the fact that
another user has the file open,
or the file is protected with a
code> 20.

CAN'T FIND LINE

BASIC

An attempt has been made to edit
a nonexistent line.

CAN'T FIND "NAME" IN SYSTEM
LIBRARY

BASIC

The requested OLD file cannot
be found.

D-2

Message
CHAIN TO BAD FILE

Program

Explanation

BASIC

The file specified by the CHAIN
has an invalid format; it is not
a BASIC format file.
IS~.~"

The "PROGRAM

message will follow this

error message.

The program name

will be the name of the bad file.

DEF STATEMENT MISSING

BASIC

A function needing a DEF statement
exists in the program.

DEVICE BUSY

BASIC

The user tried to OPEN DECtapes
0-7, line printer, or paper tape

punch, but the device was unavailable, and there was no ELSE clause
in the OPEN statement.

DIMENSION TOO LARGE

BASIC

Too large an array to fit in the
available core.

DISK FULL

BASIC

There is no more storage space
on the system disk l or the user
has exceeded his disk quota.

DUPLICATE FILE NAME

BASIC

An attempt has been made to SAVE
a program but one already exists
with that name.

D-3

Message
EXECUTE ONLY

Program

Explanation

BASIC

An attempt has been made to list,
edit, or alter a BASIC compiled
program.

FOR WITHOUT NEXT

BASIC

It may be run only.

There is an unmatched FOR statement in the program.

GET BEYOND END OF FILE

BASIC

Disk data file is too small to
have a record with the number
specified in the GET statement
at line n.

GET/PUT ERROR

BASIC

A hardware error occurred in GET
or PUT.

(This is usually due to

a DECtape unit being write-locked.)

GOSUB-RETURN ERROR

BASIC

Subroutines are too deeply nested
or a RETURN statement exists outside a subroutine.

ILLEGAL CHARACTER

BASIC

The user attempted to use an illegal character in the statement
being processed.

ILLEGAL CONSTANT

BASIC

The format of a constant in the
statement being processed is not
valid.

D-4

Messaye
ILLEGAL FORMAT

Program

Explanat~on

BASIC

The structure of the statement
does not agree with BASIC syntax.

ILLEGAL FOR NESTING

BASIC

FOR NEXT loops are too deeply
nested or NEXT appears before FOR~

ILLEGAL INSTRUCTION

BASIC

A statement was used which is not
one of the legal BASIC statements.

ILLEGAL LINE NUMBER

BASIC

The format of the line number being used in a GOTO or IF statement
is not acceptable.

ILLEGAL OPERATION

BASIC

The expression being processed
does not agree with the BASIC
rules (this is probably due to
unmatched parentheses) .

ILLEGAL SYNTAX

BASIC

The expression in a statement
does not agree with the BASIC
syntax.

ILLEGAL VARIABLE

BASIC

An illegal variable was used
in an array.

IMPROPER ACCOUNT #
ABORT
tBS

BASIC

A user logged in under account
numbers 1 (system account) or 2
(system library) and tried to run
BASIC.

D-5

This is prohibited.

Message

Program

IMPROPER DIM OR RECORD
STATEMENT

BASIC

Explanation
Syntax error in DIM or RECORD
statement, or an array name
that was previously dimensioned
is reused.

INVALID DEVICE NO.

BASIC

The device number in the file
I/O statement is not between 0
and 11 inclusive, (or X and 11
inclusive where X is a number
set by the system manager) .

INVALID RECORD NO.

BASIC

The record number must be a
number which is greater than
or equal to 0 and less than or
equal to 4095.

For DECtape I/O

the maximum record number is
limited further by the DEC tape
size.

LINE TOO LONG

BASIC

Too much has been typed.

MISUSED TAB

BASIC

The TAB function was used in
an invalid manner.

TAB can ap-

pear only in PRINT statements.

MISUSE OF CHR$

BASIC

The CHR$ function was used in
an invalid manner.

CHR$, like

TAB, can appear only in PRINT
D-6

statements.

Message
MORE?

Program

Explanation

BASIC

Not enough values have been entered in response to an INPUT
cornrnand~

The rest of the values

may be entered.

NEXT WITHOUT FOR

BASIC

The NEXT statement indicated has
no preceding FOR statement.

NO END STATEMENT

BASIC

All programs must have an END
statement.

ON INDEX OUT OF RANGE

BASIC

The value of the index is less
than one, or greater than the number of statement numbers.

OUT OF DATA

BASIC

An attempt was made to READ more
data than was supplied by the user.

PROGRAM IS "progname"

BASIC

This message may immediately folIowan error message, to identify
the current program in a series
of CHAINed programs.

If there is

no CHAIN, this message will not
occur.

PROGRAM NOT FOUND

BASIC

The file which the user tried to
access with a CHAIN statement does

D-7

not exist in his disk area.

The

PROGRAM IS message will also occur.

Message
PROGRAM TOO LARGE

Explanation

Program
BASIC

The program is too large to be
executed.

STACK OVERFLOW

BASIC

Make it smal1er~

The user programmed a situation
in which the expression is too
complicated to be executed.

SUBSCRIPT ERROR

BASIC

A negative subscript was used
for an array.

SYSTEM I-O ERROR

BASIC

BASIC was unable to perform the
desired disk I/O.

TIME LIMIT EXCEEDED

BASIC

The number of statements executed
by a job has exceeded the maximum
established by the system manager.
Generally, some error was made and
the program is caught in a loop.

TOO MUCH INPUT, EXCESS
IGNORED

BASIC

Too many values have been entered
in response to an INPUT command.

UNDEFINED LINE NUMBER

BASIC

The line number appearing in a
GOTO or an IF-THEN statement does
not appear in the program.

D-8

Message
UNOPEN DISK UNIT

Explanation

Program
BASIC

The user tried to do a GET,
PUT, or UNSAVE to device 8
or 9, without -a file being
previously opened on the device.

WHAT?

BASIC

The editor cannot understand
the command given.

ACCOUNT ERROR

CAT

A directory listing has been
requested for an account number
which CAT cannot find.

ERROR IN MFD OR UFD

CAT

A directory is bad.

The system

may have to be rebuilt.

SYSTEM ERROR

CAT

The system has returned an error
code when CAT attempted a file
operation.

D-9

Message

Program

Explanation

CAN'T ASSIGN DECTAPE

COpy

An attempt has been made to use
a DECtape which cannot be assigned, probably because it is
assigned to someone else.

CAN'T DELETE:

NAME

COpy

The named file cannot be deleted
because it is protected.

DECTAPE FULL

COpy

There is not room on the DECtape for the file.

DISK FULL

COpy

The disk is full.

?ERROR

COpy

A command line may have been
typed incorrectly.

SELECT ERROR

COpy

A DECtape unit is either not set
to REMOTE or is WRITE PROTECTed
and copy is trying to write.
Type ST to try again.

COMMAND ERROR

DECODE

A command line is formatted
improperly, one of the listed
files cannot be found, RUBOUT
has been pressed, the disk is
full for output, or there has
been some kind of file error.

D-IO

Message

Program

PROTECT ERROR

DECODE

Explanation
An attempt has been made to write
into someone else's file, write
into one~ own file which is protected or open to another user,
or read someone else's file which
is protected.

?OO.OO

FOCAL

Manual start given from console.

?01.00

FOCAL

Interrupt from keyboard via CTRL/C.

?01.40

FOCAL

Illegal step or line nurober used~

?01.78

FOCAL

Group number is too large.

?01.96

FOCAL

Double periods found in a line
number.

?01.;4

FOCAL

Group zero is an illegal line
number.

?01.:5

FOCAL

Line number is too large

?02.32

FOCAL

Nonexistent group referenced by DO.

?02.52

FOCAL

Nonexistent line referenced by DO.

?02.79

FOCAL

Storage was filled by push-down
list.

?03.05

FOCAL

Nonexistent line used after GOTO
or IF.

?03.28

FOCAL

Illegal command usedo

?04.39

FOCAL

Left of = in error in FOR or SET.

?04.52

FOCAL

Excess right terminators encountered.

?04.60

FOCAL

n-ll

Illegal terminator in FOR command.

Message
?04. : 3

Program

Explanatl.on

FOCAL

Missing argument in display
command.

?05.48

FOCAL

Bad argument to MODIFY.

?06.06

FOCAL

Illegal use of function or number.

?06.54

FOCAL

Storage is filled by variables.

?07.22

FOCAL

Operator missing in expression
or double E.

?07.38

FOCAL

No operator used before parenthesis.

?07.;6

FOCAL

Illegal function name or double
operators.

?07. : 9

FOCAL

No argument given after function
call.

?08.47

FOCAL

Parentheses do not match.

?09.11

FOCAL

Bad argument in ERASE.

?10.:5

FOCAL

Storage was filled by text.

?11.35

FOCAL

Input buffer has overflowed.

?20.34

FOCAL

Logarithm of zero requested.

?23.36

FOCAL

Literal number is too large.

?26.99

FOCAL

Exponent is too large or negative.

?28.73

FOCAL

Division by zero requested.

?30.05

FOCAL

Imaginary square roots required.

D-l2

Message-

Explanation

Program

?30.71

FOCAL

Undefined library command.

?30. 0

FOCAL

Bad argument or missing argument to library command.

?31. 7

FOCAL

Illegal character, unavailable
command, or unavailable function
used ..

?31 .. 42

FOCAL

No such name in library directory~

?31.43

FOCAL

Attempt to enter a duplicate name
in the directory.

?31.44

FOCAL

Library directory is full.

FORTRAN-D

Mixed mode arithmetic expression.

FORTRAN-D

Missing variable or constant in
arithmetic expression.

FORTRAN-D

Comma was found in arithmetic expression.

FORTRAN-D

Too many operators in this expression.

FORTRAN-D

Function argument is in fixedpoint mode.

FORTRAN-D

Floating-point variable used as a
subscript.

FORTRAN-D

Too many variable names in this
program.

FORTRAN-D

Program too large, core storage
exceeded.

FORTRAN-D

Unbalanced right and left parentheses.

D-13

Message

Program
FORTRAN-D

Explanat10n
Illegal character found in this
statement

FORTRAN-D

Compiler could not identify this
statement

FORTRAN-D

More than one statement with same
statement number

FORTRAN-D

Subscripted variable did not appear
in a DIMENSION statement

FORTRAN-D

Statement too long to process

FORTRAN-D

Floating-point operand should have
been fixed-point

FORTRAN-D

Undefined statement number

FORTRAN-D

Too many numbered statements in
this program

FORTRAN-D

Too many parentheses in this statement

FORTRAN-D

Too many statements have been
referenced before they appear in
the program

FORTRAN-D

DEFINE statement was preceded by
some executable statement

FORTRAN-D

Statement does not begin with a
space, tab, C, or number

0240

FORTRAN-D

System file error.

One of the

FORTRAN components cannot be found
or the disk is full, preventing
FORTRAN from proceeding.
calling FORT.

D-14

Try re-

Message

Program

Explanation

3100

FORTRAN-D

Illegal operator on compiler stack.

3417

FORTRAN-D

Pre-precedence error.

6145

FORTFAN-D

Could not find FOSL on system
device; if the error occurs, it
may be necessary to reload FORT
and FOSL.

6223

FORTRAN-D

Error while loading the Compiler.

6226

FORTRAN-D

Same as above.

6257

FORTRAN-D

Same as above.

6724

FORTRAN-D

No END statement on source device.

6746

FORTRAN-D

Same as above.

7114

FORTRAN-D

Same as above.

Checksum error on FORTRAN binary

input
Illegal origin or data address on

FORTRAN binary input
04

Disk input-output error

High-speed reader error

Illegal FORTRAN binary input device

Attempt to divide by zero

Floating-point input data conversion error.

Illegal op code

Disk input-output error

D-15

Message

Explanation

Program

Non-FORMAT statement used as a

FORMAT
16

Illegal FORMAT specification

Floating-point number larger than
2047

Square root of a negative number

Exponential negative number

Logarithm of a number larger than
2047

Illegal device code used in READ

or WRITE statement
System device full, could not

complete a WRITE statement
76

Stack underflow error

Stack overflow error

LOAD ERROR

LOGID

The file

given as input is not a

valid binary file.
DUPLICATE ACCOUNT #

LOGID

An attempt has been made to define
an account, but the account number
already exists with a different
password.

LOGGED IN -- NOT DELETED

LOGID

A user is logged in under an account which the manager is attempting to delete.

NOT FOUND

LOGID

An attempt has been made to delete

an account which cannot be found.

D-16

Message
OPEN FILE - NOT DELETED

Program

Explanation
=

LOGID

An account cannot be deleted because one of its files is open to
some other user.

RESTRICTED ACCESS

LOGrD

Accounts 1, 2, and 3 cannot be deleted by LOGID.

RESTRICTED ACCESS tBS

LOGID

LOGID can be run only under account 1.

SYSTEM ERROR

LOGID

An error code has been returned
from a file operation.

Possibly

someone has a file open belonging
to an account which is being deleted.

Message

Program

Explanation

ALREADY LOGGED IN

MONITOR

The user tried to log in on a
console which is already in use.

BAD DIRECTORY

MONITOR

A request cannot be honored because a disk directory is invalid.

BAD FILE NAME

MONITOR

An invalid file name has been given

BUSY

MONITOR

The user attempted to talk to a
console which is currently printing
or on which another user is typing.

DEVICE NOT AVAILABLE

MONITOR

A device which a user tried to assign is not present on the system,
or is temporarily busy and will be
free in a few seconds.

D-17

Program
MONITOR

Message
DIRECTORY FULL

Explanation
A request cannot be honored
because the user's directory
is full, or his disk quota
is exceeded.

DISK FULL

MONITOR

A request cannot be honored
because the disk is full.

DISK ERROR FOR JOB

MONITOR

There has been an error while
reading or writing in a disk
file.

MYFILE EXCEEDING
DISK QUOTA

MONITOR

The user has extended a file
beyond the allowed disk quota.
The amount of extra space
(grace) the user is allowed
is determined by the system
manager. This message is
informational only.

FAILED BY n SEGMENTS MONITOR

FILE IN USE

MONITOR

An EXTEND command caQnot be completed because the d~sk or directory is full, or the disk quota
would be exceeded.
A file ca~~o~ be altered because
it is open to another user, or
possibly twice to one user.

FILE NOT FOUND

MONITOR

A file cannot be found.

FILE NOT OPEN

MONITOR

A file request has been made, but
there is no file open on the internal file number which has been
given.

FULL

MONITOR

The system is full.

Another user

cannot log in until one of the
present users logs out.
HUNG DEVICE FOR JOB

MONITOR

A device which the user tried to
use is not responding.

For the

paper tape punch and line printer,
this message will be repeated until the device is turned on or

D-18

released.

Message

.program

Explanation

ILLEGAL lOT FOR JOB

MONITOR

The user has tried to execute an
lOT which is illegal.

This can

mean that either he has tried to
use a device which is not available, or he has executed a privileged lOT, but is not in the privileged condition at the time.

ILLEGAL REQUEST

MONITOR

The user requested an illegal command.

This error usually results

when some parameter has been given
an incorrect value or the request
refers to a facility not owned
by the user.
LOGIN PLEASE

MONITOR

The user attempted to use a console
which is not logged into the
system.

PROTECTION VIOLATION

l-10NITOR

A request cannot be honored because
of a file's protection, or because
it is open more than once.

SWAP ERROR FOR JOB

MONITOR
D-l9

These has been a disk error while
swapping the user's program.

Message
TYPE tBS FIRST

Program

Explanation

MONITOR

The user typed a command which
cannot be honored, while a program is running.

The user should

type CTRL/B followed by S, a
carriage return, and then enter
his command.

He may then type

START to continue running the program.

UNAUTHORIZED ACCOUNT

MONITOR

The user attempted to log into
the system with an invalid account
number or password.

WAIT FOR I/O

MONITOR

A command cannot be honored because of I/O in progress.

Non-Fatal
BASIC

Non-Fatal

Wait

a few seconds and try again.
An invalid character was typed
in response to an INPUT statement.
An attempt was made to compute
the logarithm of zero or a negative number.

Zero is used for

the result.

Non-Fatal
BASIC

Overflow - the result of a ca1culation was too large for the
computer to handle.

The largest

possible number is used for the
result.
D-20

Mess~ge

Program

Explanation

Non-Fatal
BASIC

An attempt was made to raise a
negative number to a fractional
power.

The absolute value of

that number raised to the fractional power is used.

Non-Fatal
BASIC

An attempt was made to compute the

square root of a negative number.
The square root of the absolute
value is used for the result.

Non-Fatal
BASIC

Underflow - the result of a calculation was too small for the computer to handle.

Zero is used for

the result.

Non-Fatal
BASIC

Zero divide - an attempt was made
to divide by zero.

The largest

possible number is used for the
result.

PAL-D

Two PAL-D internal tables have
overlapped.

This situation can

usually be corrected by decreasing
the level of literal nesting or
number of current page literals
used prior to this point on the
D-2l·

page.

Message
DE

Explanation

Program
PAL-D

System device error - An error
was detected when trying to read
or write onto the system device;
after three failures, control is
returned to the Monitor.

PAL-D

Systems device full - The capacity
of the system device has been exceeded; assembly is terminated and
control is returned to the Monitor.

PAL-D

Illegal character - An illegal
character was encountered other
than in a comment or TEXT field;
the character is ignored and the
assembly continued.

PAL-D

Illegal redefinition of a symbol An attempt was made to give a previously defined symbol a new value
by means other than the equal sign;
the symbol was not redefined.

PAL-D

Illegal equals - An equal sign was
used in the wrong context.
Examples:
TAD A+=B
A+B=C

D-22

the expression to the
left of the equal sign
is not a single symbol
or, the expression to
the right of the equal
sign was not previously
defined.

Message
II

Explanation

Program
PAL-D

Illegal indirect - An off-page reference was made; a link could not
be generated because the indirect
bit was already set.

PAL-D

The program terminator, $, is missing.

PAL-D

Current nonzero page exceeded - An
attempt was made to:
a.

override a literal with an
instruction, or

override an instruction with
a literal i this can be corrected
by
(1) decreasing the number of
literals on the page or

(2) decreasing the number of
instructions on the page.

PAL-D

Symbol table exceeded - Assembly
is terminated and control is
returned to the Monitor.

PAL-D

Undefined symbol - A symbol has
been processed during pass 2 that
was not defined before the end of

D-23

pass 1.

Message
ZE

Program
PAL-D

Explanation
Page 0 exceeded - Same as PE
except with reference to page O.

COMMAND ERROR

PIP

An illegal option has been entered.

DISK I/O ERROR

PIP

Self-explanatory.

DIRECTORY FULL

PIP

The file specified for output
cannot be written into because
the user's directory is full.

DEVICE NOT AVAILABLE OR
HUNG

PIP

A device cannot be assigned or is
hung.

Hung devices usually result

from having the device turned off.

FILE NOT FOUND

PIP

The file listed as input cannot
be found.

LOAD ERROR (nnnn)

PIP

A SAVE format paper tape was not
read properly.

nnnn = the final

checksum.

OUTPUT FILE IN USE

PIP

The output file cannot be written
into because some other user has
that file open.

D-24

Program

Message

PIP

PROTECTED

Explanation
A file cannot be accessed because
of protection.

***SYSTEM ERROR***
DISK FULL

PIP

The disk is full.

ARE YOU SUR!:?

PTJT~

The user is trying to zero a
device. To proceed, type Y.
Type anything else otherwise.

BAD CARD TRY AGAIN?

PUTR

When PUTR tried to read a card,
it did not receive 39, 40, or 80
columns.

Typing N and a carriage

return will cause PUTR to close
the output file, or typing anything
else will cause PUTR to try reading
once again.

BAD INPUT DEVICE

PUTR

An attempt has been made to input
from a device which is output only,
such as LPT:.

BAD OUTPUT DEVICE

PUTR

An attempt has been made to output
to an input-only device, such as
PTR: •

BAD SWITCH

PUTR

A switch (characters following a
slash) is invalid.

BAD SYSTEM DIRECTORY

PUTR

CAN'T ASSIGN

PUTR

DEVICE

D-25

The system Q1rectory is invalid.
The listed device cannot be
assigned. Type any character
and try again, or type CTRL/C
to give up.

Message
CAN'T DELETE

Program
PUTR

Explanation
The listed file could not be
deleted.

CAN'T OPEN INPUT

PUTR

The file listed as input cannot
be opened.

CAN'T OPEN OUTPUT

PUTR

The desired output file cannot
be opened.

CREATE ERROR

PUTR

A file with the desired name
cannot be created on the system
disk.

Perhaps one with that name

already exists and is protected.

DECTAPE STATUS B ERROR

PUTR

An error has occurred while readlng or writing a DECtape. The
error code is in the switch
register, which can be found
by typing CTRL/B, then W, then
RETURN

DIRECTORY FULL

PUTR

ILLEGAL SYNTAX

PUTR

The DECtape or RK¢5 directory
has no more room.
PUTR cannot understand the command
which was typed.

ILLEGAL UNIT

PUTR

The unit number for DECtape or
RK8E was invalid.

INPUT ERROR

PUTR

There has been an error while
reading from the input device.

LINE TOO LONG

PUTR
D-26

The command line just typed was
too long for PUTR.

Message

Program

NOT UNDER ACCOUNT 1

PUTR

PUTR must never be run under
account 1.

NO END OF FILE

PUTR

When reading a BASIC file, the
physical end of the file was
found before the logical end
of file.

FILES FOUND

Pl.JTR

The user has requested some
operation, but PUTR has found
no files to operate upon.

OLD DECTAPE

PUTR

An attempt has been made to
output to a DECtape which is
neither OS/8 nor PUTR format.

OUTPUT FILE TOO LARGE

PUTR

There is not room for the
output file.

PUTR2 APPEND ERROR

PUTR2

PUTR2 could not successfully
append itself to PUTR. Perhaps PUTR is being used by
another user, has already had
PUTR2 appended to it, is not
the same version as PUTR2, or
the disk is full.

RK,05 I/O ERROR

PUTR

There has been an error while
reading or writing on the RK,05.
The status can be found in the
switch register which can be
found by typing CTRL/B followed
by SW and RETURN.

Explanat~on

RK,05 NOT READY?

PUTR

The RK¢5 is not ready or writelocked. Type CTRL/C to abort
the operation or any other
character to try again.

SELECT ERROR?

PUTR

A DECtape unit is not on remote
or not write enabled. Type a
carriage return to try again or
CTRL/C to abort the operation.

SYSTEM READ ERROR

PUTR

There has been an error while
reading from the system disk.

SYSTEM WRITE ERROR

PUTR

There has been an error while
writing to the system disk.

USE DEL *

PUTR

Zero is an invalid command for
SYS: .

WHAT?

PUTR

PUTR cannot understand the
command just typed.

HOW TO OBTAIN SOFTWARE INFORMATION
SOFTWARE NEWSLETTERS, MAILING LIST
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Newsletters are published monthly, and keep the user informed about customer software problems and solutions, new software products, documentation corrections, as well as programming notes and techniques.
There are two similar levels of service:
The Software Dispatch
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The Software Dispatch is part of the Software Maintenance Service. This
service applies to the following software products:
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RSTS-E
DECsystem-lO
A Digital Software News for the PDP-II and a Digital Software News for
the PDP-8/l2 are available to any customer who has purchased PDP-ll or
PDP-8/l2 software.
A collection of existing problems and solutions for a given software
system is published periodically. A customer receives this publication
with his initial software kit with the delivery of his system. This
collection would be either a Software Dispatch Review or Software Performance Summary depending on the system ordered.
A mailing list of users who receive software newsletters is also maintained by Software Communications. Users must sign-up for the newsletter they desire. This can be done by either completing the form supplied with the Review or Summary or by writing to:
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SOFTWARE PROBLEMS
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as follows:
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Upon completion of Software Performance Report (SPR) form remove last
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The acknowledgement copy will be returned along with a blank SPR form
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Software and manuals should be ordered by title and order number. In the
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Outside of the united States, orders should be directed to the nearest
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USERS SOCIETY
DECUS, Digital Equipment Computers Users Society, maintains a user exchange center for user-written programs and technical application information. The Library contains approximately 1,900 programs for all
DIGITAL computer lines. Executive routines, editors, debuggers, special
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DECUS Program Library Catalogs are routinely updated and contain lists
and abstracts of all programs according to computer line:
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PDP-7/9, 9, 15
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PDP-6/l0, 10
Forms and information on acquiring and submitting programs to the DEC US
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In addition to the catalogs, DECUS also publishes the following:
DECUSCOPE
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aimed at facilitating the interchange of technical information among users of DIGITAL computers and at disseminating news items concerning the Society. Circulation reached 19,000 in May, 1974.
PROCEEDINGS OF
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THE DIGITAL
in Europe, Australia, and Canada.
EQUIPMENT USERS
SOCIETY
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MINUTES OF THE
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DECsystem-10
SESSIONS
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COPY-N-Mail
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application.
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READER'S COMMENTS
NOTE:

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SOFTWARE INFORMATION page).

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