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Document:	Advanced Software System Monitors
Order Number:	DEC-9A-MAD0-D
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Pages:	222
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Digital Equipment Corporation
Maynard, Massachusetts

mamaama

ADVANCED SOFnNARE
SYSTEM MON ITORS

ADVANCED SOFnNARE
SYSTEM MONITORS

For additional copies order No. DEC-9A-MADO-D from Program library,
Digital Equipment Corporation, Maynard, Massachusetts.
DIGITAL EQUIPMENT

CORPORATION

Printed in U.S.A.

Price $5.00

MAYNARD. MASSACHUSETTS

1st Printing March 1967
2nd Printing Revised February 1968
3rd Printing Revised May 1968
4th Printing Revised January 1968

Instruction times, operating speeds and the like are included in this manual for reference only; they are not to
be taken as specifications.

The following are registered trademarks of Digital
Equipment Corporation, Maynard, Massachusetts:
DEC
FLIP CHIP
DIGITAL

PDP
FOCAL
COMPUTER LAB

CONTENTS

CHAPTER 1
PDP-9 ADVANCED SOFTWARE SYSTEM

1.1

Introduction

1-1

1.2

Hardware Requi rements

1-1

1.3

Monitor Systems

1-2

1. 3. 1

Input/Output Monitor

1-2

1.3.2

Keyboard Monitor

1-3

1.3.3

Background/Foreground Monitor

1-3

1.4

Input/Output Programming System (lOPS)

1-4

1.5

System Programs

1-4

1 .5. 1

FORTRAN IV Compiler

1-5

1.5.2

MAC RO -9 Assemb ler

1-5

1.5.3

Dynamic Debugging Technique (DDT) Program

1-6

1.5.4

Text Editor Program

1-6

1 .5.5

Peripheral Interchange Program (PIP)

1-7

1.5.6

Linking Loader

1-7

1.5.7

PDP-7 to MACRO-9 Assembly Language Converter

1-7

1 .5.8

System Generator

1-7

1.5.9

Dump Program

1-8

1.5.10

Library Update Program

1-8

1. 5. 11

System Patch Program

1-8

1.5.12

Chain Builder and Execute Programs

1-8

CHAPTER 2
THE PDP-9 MONITOR ENVIRONMENT

2. 1

2-1

Monitor Functions

2. 1 . 1

General I/O Communication

2-1

2.1.2

Command, Control, and Data Flow

2-2

2.2

Line Buffers

2-5

2.3

Data Modes

2-8

2.3.1

lOPS Modes

2-9

2.3.2

Image Modes

2-10

2.3.3

Dump Mode

2-10

2.3.4

Input/Output Data Mode Terminators

2-11

iii

CONTENTS (cont)
Page
2.4

2-12

System Tables

2.4. 1

Device Assignment Table {. DAT}

2-12

2.4.2

System Communication Table (.SCOM)

2-13

Specifying Devices Used To Linking Loader

2-14

2.5

CHAPTER 3
USER PROGRAM COMMANDS (SYSTEM MACROS)
3.1

I/O Monitor Commands (System Macros)

3-1

3. 1 . 1

· I NIT (Initi al i ze)

3-2

3. 1 .2

. READ

3-2

3. 1.3

. WRITE

3-3

3.1.4

. WAIT

3-4

3.1.5

.WAITR

3-4

3.1.6

.CLOSE

3-5

3. 1 .7

· TIMER

3-5

3. 1.8

· EXIT

3-6

3.2

Keyboard Monitor Commands {System Macros}

3-7

3.2. 1

.SEEK

3-7

3.2.2

· ENTER

3-8

3.2.3

• FSTAT

3-9

3.2.4

.RENAM

3-9

3.2.5

· DLETE

3-10

3.2.6

.TRAN

3-10

3.2.7

.CLEAR

3-11

3.2.8

.MTAPE

3-11

3.3

Background/Foreground Monitor Commands (System Macros)

3-12

3.3.1

.REALR

3-12

3.3.2

· REALW

3-13

3.3.3

.IDLE

3-15

3.3.4

.IDLEC

3-15

3.3.5

· TIMER

3-15

3.3.6

· RLXIT

3-16

CONTENTS (cont)
Page
CHAPTER 4
INPUT/OUTPUT MONITOR
4. 1

Input/Output Monitor Functions

4-1

4.2

Programming Example

4-1

4.3

Operating The I/O Monitor System

4-3

4.3. 1

Loading Program in the I/O Monitor Environment

4-3

4.3.2

Device Assignments

4-8

4.3.3

Error Detection and Handling

4-9

4.3.4

Control Character Commands in the I/O Monitor Environment

4-10

4.3.5

Modifying System Programs and Bui Iding Executable User Core
Loads in the I/O Monitor Environment

4-10

CHAPTER 5
KEYBOARD MONITOR
5. 1

Keyboard Monitor Functions

5-1

5.2

Programming Example

5-1

5.3

Keyboard Commands

5-4

5.3.1

System Program Load Commands

5-4

5.3.2

Special Function Commands

5-5

5.3.3

Control Character Commands

5-12

5.4

Operating The Keyboard Monitor System

5-13

5.4.1

Loading the Keyboard Monitor

5-13

5.4.2

System Generation

5-14

5.4.3

Assigning Devices

5-19

5.4.4

Loading Programs in the Keyboard Monitor Environment

5-20

5.4.5

Error Detection and Handling

5-21

5.5

Batch Processing

5-26

5.6

DECtape File Organization

5-29

5.6. 1

Non-File-Oriented DECtape

5-29

5.6.2

File-Oriented DECtape

5-29

5.7

5-32

Interim Disk System

5.7. 1

The Disk as System Device

5-33

5.7.2

Disk File Organization

5-33

5.8

Disk System Operation

5-34

CONTENTS (cont)
Page

5.8.1

Paper Tape Load Procedure

5-35

5.8.2

Disk System Generation

5-37

5.8.3

Disk System Generation from DECtape

5-37

5.8.4

Disk System Save/Load from DECtape

5-38

Magnetic Tape Systems

5-39

5.9.1

File Organization

5-40

5.9.2

File Identification and Location

5-42

5.9

5.10

Magnetic Tape System Operation

5-44

5.10.1

System Fi Ie Structure

5.10.2

System Tape Organization

5-44
5-45

5.10.3

System Startup

5-45

5.10.4

Continuous Operation

5-46

5.11

5-47

Drum File Organization
CHAPTER 6
BACKGROUND/FOREGROUND MONITOR

6.1

Background/Foreground Monitor Functions

6-1

6.1.1

Scheduling of Processing Time

6-2

6.1.2

Protection of FOREGROUND Job Core and I/O

6-4

6. 1.3

Sharing of Multi-Unit Device Handlers

6-4

6.1.4

Use of Software Priority Levels

6-5

6.1.5

Use of Real-Time Clock

6-5

6.1.6

Communication Between BACKGROUND and FOREGROUND Jobs 6-5

6.2

Hardware Requirements and Options

6-5

6.3

Keyboard Commands

6-7

6.3. 1

FILES

6-7

6.3.2

FCORE

6-7

6.3.3

FCONTROL

6-7

6.3.4

BCONTROL

6-8

6.4

Operating the Background/Foreground Monitor System

6-8

6.4.1

Loading the Background/Foreground Monitor

6-9

6.4.2

Assigning Devices

6-9

6.4.3

Loading User FOREGROUND Programs

6-9

6.4.4

Loading System or User BACKGROUND Programs

6-10

CONTENTS (cont)
Page

6.4.5

End of Job

6-11

6.4.6

Error Detection and Handling

6-12

CHAPTER 7
I/O DEVICE HANDLERS
7. 1

Description of I/O Hardware and API Software Level Handlers

7-1

7.1.1

I/O Device Handlers

7-1

7.1.2

API Software Level Handlers

7-4

7.1.3

Standard API Channel/priority Assignments

7-6

7.2

Writing Special I/O Device Handlers

7-6

7.2.1

Discussion of Example A by Parts

7-8

7.2.2

Example A, Skeleton I/O Device Handler

7-9

7.2.3

Example B, Special I/O Handler for Type AF01 B A/D Converter

7-11

7.2.4

Incorporating Special, User-Program I/O Handler into Paper
Tape System

7-14

7.3

I/O Handlers Acceptable to System Programs

7-15

7.4

Summary of Standard I/O Handler Features

7-21

APPENDIX A
PDP-9 ASCII CHARACTER SET
APPENDIX B
PDP-9 ASCII/HOLLERITH CORRESPONDENCE
APPENDIX C
KEYBOARD AND BACKGROUND/FOREGROUND MONITOR ERRORS
APPENDIX D
LINKING LOADER AND SYSTEM LOADER ERRORS
APPENDIX E
lOPS ERRORS
APPENDIX F
SYSTEM PROGRAM DISK AND DECTAPE ADDRESSES
APPENDIX G
SUMMARY OF KEYBOARD COMMANDS
FOR KEYBOARD AND BACKGROUND/FOREGROUND MONITORS

vii

CONTENTS (cont)

ILLUSTRATIONS

2-1

General I/O Communication in Monitor Environment

2-2

Command, Control, and Data Flow in Monitor Environment

2-3

Monitor Commands and Function Codes

2-4

line Buffer Structure

2-6

2-5

Format of Header Word Pair

2-7

2-6

lOPS Mode Data on Paper Tape

2-9

2-7

5/7 ASCII Packing Scheme

2-10

2-8

Image Mode Data on Paper Tape

2-11

2-9

lOPS ASCII and Image Alphanumeric Data in line Buffers

2-11

4-1

I/O Mon i tor System Memory Maps

4-5

4-2

Device Assignment Table (.DAT) for I/O Monitor

4-8

4-3

Device Assignment Table (.DAT) for PIP

4-9

5-1

Function of • DAT Slots in Keyboard Monitor System

5-20

5-2

Keyboard Monitor System Memory Maps

5-22

5-3

Paper Tape Block Format

5-35

5-4

Block Format, Fi Ie-Structured Mode

5-41

5-5a.

Format of the File Directory Data Block

5-43

5-5b.

Format of Fi Ie-Structured Tape

5-43

5-6a.

User-Fi Ie Header Label Format

5-44

5-6b.

User-File Trailer label Format

5-7a.

System Program (PIP) Header Label

5-7b.

System Program (PIP) Trailer Label

5-44
5-45
5-45

6-1

Keyboard Communication in Background/Foreground Monitor System

6-2

Background/Foreground Monitor System Memory Maps

6-13

7-1

Structure of API Software Level Handler

7-5

7-2

lOPS Binary Input Card Format

7-36
TABLES

2-1

Maximum line Buffer Sizes

2-8

2-2

Input/Output Data Mode Terminators

2-12

2-3

System Communication Table (.SCOM) Entries

2-13

4-1

Control Character Commands

4-10

viii

TABLES (cont)
Page

5-1

5-12

Control Character Commands

PREFACE

This manual contains information required to prepare programs for operation under
control of PDP-9 ADVANCED Software System Monitors.

The manual is organized

as follows:
Chapter 1

PDP-9 ADVANCED Software System

Chapter 2

The PDP-9 Monitor Environment

Chapter 3

User Program Commands (System Macros)

Chapter 4

Input/Output Monitor

Chapter 5

Keyboard Monitor

Chapter 6

Background/Foreground Monitor

Chapter 7

I/O Device Handlers

The I/O Monitor (Chapter 4) is used with paper tape systems; the more sophisticated
Keyboard Mon itor (Chapter 5) is used with bulk storage systems; and the Background/
Foreground Monitor (Chapter 6) is used with time-shared and real-time systems.

Up-

ward compatibility exists between the monitor systems. The Keyboard Monitor contains all the features of the I/o Monitor and also provides for Teletype keyboard
commands. The Background/Foreground Monitor is an extension of the Keyboard
Monitor and provides for concurrent BACKGROUND and FOREGROUND processing.
An I/O Monitor Guide and a Keyboard Monitor Guide, prepared especially for
convenient use at the computer console, are now available (Order Numbers DEC9A-MIPA-D

and DEC-9A-MKFA-D, respectively). These console manuals sum-

marize the essential information required to operate the I/O and Keyboard Monitors,
and include detailed operating procedures for each of the system programs.

It should be noted that all material presented in this manual for the Background/
Foreground Monitor is preliminary and subject to change.

CHAPTER 1
PDP-9 ADVANCED SOFTWARE SYSTEM

1.1

INTRODUCTION
PDP-9 ADVANCED software provides a complete system for program preparation, compilation,

assembly, debugging, and operation. It features total relocatability and can expand to take full advantage of any hardware configuration. Powerful system programs include FORTRAN IV, a sophisticated
macro assembler, an on-line debugging system, an on-line editor, and a peripheral interchange program.
A versatile and flexible input/output programming system frees the user from the need to create devicehandling subroutines and the concerns of device timing.
Three monitor systems are available with PDP-9 ADVANCED software. The Input/Output
Monitor operates on a basic PDP-9 with 8192 (or more) words of memory, high-speed paper tape reader
and punch, and a console teleprinter. The I/O Monitor operates in a paper tape (or card) environment
and provides for the calling and handling of all input and output functions.
The more sophisticated Keyboard Monitor is available for systems with auxiliary bulk storage
units. It allows for device-independent programming and automatic creation, calling, and loading of
programs. Since upward compatibility exists between the Input/Output Monitor and the Keyboard
Monitor, all programs prepared for the I/O Monitor can also be run using the Keyboard Monitor.
The Background/Foreground Monitor is an extension of the Keyboard Monitor. It allows for
the concurrent, time-shared use of a PDP-9 system by a protected FOREGROUND user program and an
unprotected BACKGROUND system or user program. This provides the user with optimum utilization of
system hardware and processing time.

1.2

HARDWARE REQUIREMENTS
To operate the PDP-9 ADVANCED software system under control of the Input/Output Monitor,

a basic PDP-9 is required with:
a.

8192 words of core memory

300 character per second paper tape reader

50 character per second paper tape punch

Console teleprinter (Teletype Model KSR 33 or KSR 35)

For extra memory, the Type K E09A Extended Arithmeti c Element and the Type KF09A Automatic Priority Interrupt can also be used with this system. The Type CR02B Card Reader can be used
for input in addition to the paper tape reader; a Type 647 Line Printer can be used for listings.

1-1

Some form of bulk storage must be added to the basic PDP-9 to use the Keyboard Monitor:
a.

Type TC02 DECtape Control and two Type TU55 DECtape Transports, or

b. Type TC59 Magnetic Tape Control and two 7-channel or 9-channel Magnetic Tape
Transports (Type TU20, Type TU20A, or equivalent), or
c.

Type RC09 Fixed-Head Disk System

Input/output routines are provided for these devices as required. In addition, this system
can take full advantage of extra memory, central processor options, and additional I/O options.
The Background/Foreground Monitor requires all the options itemized for the Keyboard Monitor plus the following:
a. Type LT09A** Multi-station Teletype Control, and one Type LT09B Line Unit for each
external Teletype.

1.3

Type KSR 33 Teletype

Type KX09A Memory Protection Option

Type KG09A Memory Extension Control

Type MM09A Memory Module (8K)

MONITOR SYSTEMS
PDP-9 monitor systems simplify the handling of input/output functions and facilitate the

creation, debugging, and use of PDP-9 programs. They allow overlapped input/output and computation,
simultaneous operation of a number of asynchronous peripheral devices, and (in the case of the Keyboard
and Background/Foreground Monitors) device-independent programming, while freeing the user from
the need to create device handling subroutines. The monitors, operating in conjunction with the Input/
Output Programming System (lOPS), provide a complete interface between the user's programs and the
peripheral hardware. The Background/Foreground Monitor effectively provides the user with two systems; on-line data acquisition and control can be performed in the FOREGROUND while user program
compilation, debugging, etc., can be accomplished in the BACKGROUND environment.

1 .3. 1

Input/Output Monitor
The Input/Output Monitor accepts I/O commands from the system or user programs and super-

vises their execution. By calling upon the device manipulation routines of lOPS, it provides for simultaneous I/O and computation.

* Background/Foreground systems cannot use magneti c tape as a system devi ce.
**If the API option is available, a Type LTl9A Teletype Control and a Type LTl9B Line Unit are required instead of the LT09A and LT09B.

1-2

The I/O Monitor contains:
a.

Routines for its own initialization and control.

b. Tables to allow communication between the Monitor, system programs, user programs,
and the Input/Output Program System.
c.

The CAL Handler, which is used to dispatch to the appropriate Monitor and I/O sub-

Device handlers for the Teletype and clock.

routines.

The I/O Monitor resides in lower core and occupies about 960 10 locations.
1.3.2

Keyboard Monitor
The Keyboard Monitor is designed to operate on a PDP-9 system with some form of auxiliary

bulk storage (see Hardware Requirements, Section 1.2). It includes all of the facilities of the I/O
Monitor plus routines to accept and act upon Teletype keyboard commands, the ability to dynamically
modify I/O device assignments for a program, and the facilities for automatically storing, calling,
loading, and executing system and user programs.
With the ability to alter I/O assignments, the Keyboard Monitor brings true device independence to the user. Programs may be modified simply and quickly to operate on any configuration, and
additions to (or deletions from) an existing system need not result in program reassembly or recompilation.
The Keyboard Monitor also frees the user from the problems of tape or card handling. Programs can be created, stored, retrieved, loaded, debugged, and operated at the keyboard console.
Both system and user programs can be called from the bulk storage device with a few simple keyboard
commands. The Keyboard Monitor also has a batch processing capability that allows user commands to
come from the paper tape reader (or card reader) instead of the Teletype, perm itti ng many programs
to be run without operator intervention.

1.3.3

Background/Foreground Monitor
The Background/Foreground Monitor is designed to control processing and I/O operations in

a real-time or time-shared environment. FOREGROUND programs are defined as the higher priority,
debugged programs that interface with the real-time environment. They normally operate under Program
Interrupt (PI) or Automatic Priority Interrupt (API) control. At load time they have top priority in
selection of core memory and I/O devices, and at execution time they have priority (according to the
assigned priority levels) over processing time and use of shared I/O.
BACKGROUND processing is essentially the same as processing normally performed under
control of the Keyboard Monitor. That is, it could be an assembly, compilation, debugging run,

1-3

production run, editing task, etc. BACKGROUND programs may use any facilities (core, I/O, or
processing time) that are available and not simultaneously required by the FOREGROUND job.
1.4

INPUT/OUTPUT PROGRAMMING SYSTEM (lOPS)
The Input/Output Programming System (lOPS) consists of an I/O control routine and indivi-

dual hardware device handling subroutines that process file and data level commands to the devices.
These handlers exist for all standard PDP-9 peripherals (see Section 7.4).
The I/O control routine accepts user program commands and transfers control to the appropriate device handlers. These device handlers are responsible for transferring data between the program
and I/O devices, for initiating the reading or writing of files, for the opening and closing of files, and
for the performance of all other functions peculiar to a given hardware device. They are also responsible for ignoring functions which they are incapable of handling (for example, trying to rewind a card
reader, or skipping files on a non-file-oriented device). All device handlers operate either with or
without the Automatic Priority Interrupt (API) option.
1.5

SYSTEM PROGRAMS
PDP-9 ADVANCED software systems include either the Input/Output Mon itor, the Keyboard

Monitor, or the Background/Foreground Monitor in addition to an Input/Output Programming System
and the following system programs:
FORTRAN IV Compiler, Object Time System, and Science Library
MACRO-9 Assembler
Dynamic Debugging Technique (DDT) Program
Text Editor Program
Peripheral Interchange Program
Linking Loader
PDP-7 to MACRO-9 Assembly Language Converter
Chain Bui Ider Program
Chain Execute Program
System Generator

With Keyboard and Background/Foreground
Monitor systems only

Dump Program
Library Update Program
System Patch Program

The following special-purpose utility programs are also available:
Disk/DECtape Save
Disk/Paper Tape Save

}

for Disk users

PUNCH9 - for paper tape systems

1-4

1.5.1

FORTRAN IV Compiler
The PDP-9 FORTRAN IV compiler is a two-pass system that accepts statements written in the

FORTRAN IV language and produces a relocatable object program capable of being loaded by the Linking Loader. It is completely compatible with USA FORTRAN IV, as defined in USA Standard X3.9-1966,
with the exception of the following features which were modified to allow the compiler to operate in
8192 words of core storage:
a.

Complex arithmetic is not legal.

b. Adjustable array dimensions are not allowed at source level, but may be implemented
by call ing dimension-adjustment subroutines.
c.

Blank Common is treated as named Common except when object program is used in

The implied DO feature is not included for the DATA statement.

Specification statements must be strictly positioned and ordered.

chaining.

The FORTRAN IV compiler operates with the PDP-9 program interrupt or API facilities enabled. It generates programs that operate with the program interrupt or API enabled and can work in
conjunction with assembly language programs that recognize and service real-time devices. Subroutines
written in either FORTRAN IV or MACRO-9 assembly language can be loaded with and called by
FORTRAN IV main programs. Comprehensive source language diagnostics are produced during compilation, and a symbol table is generated for use in on-line debugging with DDT.
There are two versions of the FORTRAN IV compiler; F4 is the basic compiler, and F4A is
an abbreviated version that allows for DECtape I/O in an 8K system. F4A does not provide for object
code listing, symbol table listing, EQUIVALENCE statements, ASSIGN statements, assigned GOTO
statements, or EXTERNAL statements.
The PDP-9 FORTRAN IV Compiler, Object Time System, and Science Library are described
fully in the FORTRAN IV Manual (DEC-9A-KFZA-D).

1.5.2

MACRO-9 Assembler
The MACRO-9 Assembler provides PDP-9 users with highly sophisticated macro generating

and calling facilities within the context of a symbolic assembler. MACRO-9 is described in detail in
the MACRO-9 Assembler Manual (DEC-9A-AMZA-D). Some of the prominent features of MACRO-9
include:
a.

The abi lity to (1) define macros
(2) define macros within macros (nesting)
(3) re-define macros (in or out of macro definitions)

1-5

(4) call macros within macro definitions
(5) have macros call themselves (recursion)
b.

Conditional assembly based on the computational results of symbols or expressions.

Repeat functions.

Boolean manipulation.

Optional octal and symbolic listings.

f. Two forms of radix control (octal, decimal) and two text modes (ASCII and 6-bit
tri mmed ASCII).
g.

Global symbols for easy linking of separately assembled programs.

h. Choice of output format: relocatable, absolute binary (check summed); or full binary
capable of being loaded via the hardware READIN switch.
i.

Ability to call input/output system macros that expand into lOPS calling sequences.

A shorter version of the assembler (MACRO A) is avai lable to enable users with 8K systems
to use DECtape for input and output. Conditional pseudo-ops and .ABS, .FUll, .REPT, and .DEFIN
are not allowed.

1.5.3

Dynamic Debugging Technique (DDT) Program
DDT provides on-line debugging facilities within the PDP-9 ADVANCED software system,

enabling the user to load and operate his program in a real-time environment while maintaining strict
control over the running of each section. DDT allows the operator to insert and delete breakpoints,
examine and change registers, patch programs, and search for specific constants or word formats.
The DDT -9 breakpoint feature allows for the insertion and simultaneous use of up to four
breakpoints, anyone (or all) of which may be removed with a single keyboard command. The search
facility allows the operator to specify a search through any part or all of an object program with a
printout of the locations of all registers that are equal (or unequal) to a specified constant. This search
feature also work, for portions of words as modified by a mask. With DDT -9, registers may be examined
and modified in either instruction format or octal code, and addresses may be specified in symbolic
relative, octal relative, or octal absolute. Patches may be inserted in either source language or octal.
DDT -9 is described more fully in the PDP-9 Utility Program Manual (DEC-9A-GUAB-D).

1.5.4

Text Edi tor Program
The Text Editor of the PDP-9 ADVANCED software system provides the ability to read alpha-

numeric text from any input device (paper tape reader, card reader, disk, DECtape, magnetic tape,
etc.), to examine and correct it, and to write it on any output device. It can also be used to create
new symbo Ii c programs.

1-6

The Editor operates on lines of symbolic text delimited by carriage return (CR) or ALT MODE
characters. These lines can be read into a buffer, selectively examined, deleted or modified, and
written out.

New text may be substituted, inserted, or appended.

For further details on the Text Editor, refer to the PDP-9 Utility Programs Manual (DEC9A-GUAB-D).

1.5.5

Peripheral Interchange Program (PIP)
The primary function of PIP is to facili.tate the manipulation and transfer of data files from

any input device to any output device. It can be used to refresh mass storage file directories, list file
directory contents, delete, insert, segment, or combine files, perform code conversions, and copy
tapes.
Directions for the use of PIP-9 can be found in the PDP-9 Utility Programs Manual (DEC9A-GUAB-D).

1.5.6

Linking Loader
The Linking Loader loads any PDP-9 FORTRAN IV or MACRO-9 object program which exists

in relocatable format (or absolute format if pseudo-ops .ABS and .FULL are not used). Its tasks include
loading and relocation of programs, loading of called subroutines, retrieval and loading of implied
subroutines, and building and relocation of the necessary symbol tables. Its operation is discussed in
the PDP-9 Utility Program Manual (DEC-9A-GUAB-D).

1.5.7

PDP-7 to MACRO-9 Assembly Language Converter
This system program converts source programs written in PDP-7 or BASIC PDP-9 assembly

language to a format acceptable to the MACRO-9 assembler.
CONV is described more fully in the PDP-9 Utility Programs Manual (DEC-9A-GUAB-D).

1.5.8

System Generator
The System Generator (SGEN) is a standard system program used to create new system tapes.

With it, the user can tailor his system to his installation's needs and specify standard input and output
devices, memory size, and special I/O and central processor options present. A more complete description of SGEN and details of its use, are given in the Keyboard Monitor Guide (DEC-9A-MKFA-D).

1-7

1.5.9

Dump Program
This system program gives the user the ability to output on any listing device, specified core

locations that have been preserved on a bulk storage file via the CTRL Q Keyboard Monitor dump command. A more complete description of the Dump program is given in the Keyboard Monitor Guide
(DEC-9A-MKFA-D).

1.5.10

Library Update Program
This system program gives the user the capability to examine and update the binary library

files on file-oriented devices. A more complete description of the Library Update program is given in
the Keyboard Monitor Guide (DEC-9A-MKFA-D).

1.5.11

System Patch Program
The System Patch program is used to make corrections to the binary version of non-relocatable

system programs on the system device. A more complete description of the System Patch program and
details of its use, are given in the Keyboard Monitor Guide (DEC-9A-MKFA-D).

1.5.12

Chain Builder and Execute Programs
The Chain Builder and Execute programs provide the user with a capability for program seg-

mentation which allows for multiple core overlap of executable code and certain types of data areas.
A more complete description of the Chain Builder and Execute programs is given in the Keyboard
Monitor Guide (DEC-9A-MKFA-D).

1-8

CHAPTER 2
THE PDP-9 MONITOR ENVIRONMENT

2.1

MONITOR FUNCTIONS
PDP-9 ADVANCED Software System Monitors greatly simplify the task of programming I/O

functions by providing an interface between system or user programs and the external world of I/o
devi ces. Upward compatibi lity exists between the Monitor systems; programs written to operate under
contro I of the I/o Monitor wi II a Iso operate, without modi fi cati on, under contro I of the Keyboard
and Background/Foreground Monitors. The Monitors, by means of the Input/Output Programming
System (IOPS) and Program Interrupt (PI) or Automati c Priori ty Interrupt (API), allow si mu Itaneous operation of multi pie I/o devices a long with overlapping computati ons.
Certain features such as the genera I monitor environment, data handling, and logi ca I/physi cal I/O device associations, are common to all three monitors. These features are discussed at length
in this chapter. It is recommended that the reader become thorough Iy fami liar with the contents of this
chapter before reading chapters that apply to each of the monitors.

2 .1 .1

General I/o Communication
The general communication required to accomplish an I/o task is the same for all three

monitor systems (see Figure 2-1). A system or user program initiates an I/o function by means of a
monitor command (system macro), which is interpreted by a CAL handler within the monitor as a legitimate I/o call. (See the PDP-9 User Handbook for a description of the CAL instruction.) The I/o call
includes a logical I/o device number as one of its arguments. The monitor establishes the logical/
physical I/O device association by means of its Device Assignment Table (.DAT). When this has been
accomplished, the monitor passes control to the appropriate device handler subroutine to initiate the
I/o functi on and return contro I to the system or user program. The system or user program retai ns
control until an interrupt (PI or API) occurs, at which time it relinquishes control to the device handler
to perform and/or complete the specified I/o function. Computations or other processing can be performed by the system or user program while waiting for an interrupt. This feature allows the programmer
to make optimum use of avai lable time.

2-1

DATA

~
SYSTEM OR
USER PROGRAM

CONTROL RETURN

Figure 2-1

2.1 .2

V I A CAL
HANDLER

VIA CAL

I/O DEVICE HANDLER

VIA PI
OR API
I/O DEVICE

MON ITOR
INITIATION \ INTERRUPT

•

General I/o Communication in Monitor Environment

Command, Contro I, and Data Flow
Figure 2-2 provides a more detai led representation of the monitor environment, with emphasis

on command, control, and data flow. As shown, the user can initiate a command via the Teletype. In
the I/o Monitor environment, this command can be interpreted only by a Command Processor within the
system program (or user program if so designed). In the Keyboard and Background/Foreground Monitor
environments, an expanded set of keyboard commands can a Iso be interpreted by a Keyboard Listener
(.KUST) and acted upon by a Monitor Command Decoder (.MCD). This feature greatly extends the
capabilities of the monitors and provides the user with a large repertoire of keyboard commands. The
monitor shown in Figure 2-2 can represent anyone of the monitor systems, except that the I/o Monitor
does not contain the .KUST and .MCD programs to interpret and act upon Teletype keyboard commands.
The .KUST and .MCD programs are nonresident in the sense that they are overlaid by user and system
programs.
Each system or user program must internally set up line buffers (except when using Dump mode,
discussed later) to be used in transmitting data to or from the external environment. Each line buffer of
n words consists of a two-word header {referred to as a header word pair} and n -2 words of data. The
system or user program can exercise control on output by modifying the header word pair, or it can
verify on input by examining the header word pair. The use of line buffers is discussed in more detail
later in this chapter.
Monitor I/o commands {system macros} are written as part of the system or user program. In
FORTRAN IV source programs, these commands are in the form of READ and WRITE statements {refer to
the FORTRAN IV Manual, DEC-9A-AF4B-D}. These statements are translated by the compiler into the
proper calling sequences for the FORTRAN Object Time System which provides the required monitor
calls at execution time. In MACRO-9 source programs, monitor I/O commands are written as system

2-2

MONITOR ENVIRONMENT

EXTERNAL ENVIRONMENT

~ Y-;O A-;D -;::N';-B;;' I

I MON ITOR SYSTEMS ONLY I

KEYBOARD COMMANDS

I
COMMAND
I
ACKNQWL EDGE ME N TS

ERROR
COMMANDS
USER

MESSAGES

TELETYPE
COMMANDS
II

ERRORS

PROGRAM
OUTPUT CONTROL

MONITOR

MON I TOR ERROR
DIAGNOSTIC LMED)

•

SYSTEM
OR USER
PROGRAM

COMMAND
PROCESSOR

ACKNOWLEDGEMENTS

IN PUT

HEADER

VERIFICAT ION

MONITOR

WORD PAIR

I
I
I
I DATA
I
I
I
I
I
I
I
I
I
I
I
L
I ______

I
I
I

ERROR MESSAGES AND COMMAND ACKNOWLEDGEMENTS

II
M(O:I\~~ T C)OM~~~D
I

KEYBOARD LISTENER

DECODER I.MCDI

L_ - - - - _.J
ERRORS
DEVICE ASSIGNMENT]
TABLE LOAl)

COMMANDS
(SYSTEM MACROS)

CONTROL

DATA

LIN E

CAL

HANDLER

BUFFER

NON I/O
FUNCT IONS MON! TOR
~I CONTROL
ROUTINE

11/0

FUNCTIONS' -

ERRORS

MONITOR

,-----

I/O CONTROL
ROUTINE

I
I

_________ -.---J

lOPS

I/O
DEvICE

DATA AND CONTROL

I
I
I

INTERRUPT

:
I
I

INITIALIZATION

INITIATION

ERRORS

I/O DEVICE HANDLER

I
I
I
I
I
I
I
I
I
I

---------------------------- ~
INPUT /OUTPUT PROGRAMMING SYSTEM (lOPS)

Figure 2-2 Command, Control, and Data Flow in Monitor Environment

macros withi n the system or user program. These system macros are expanded at assemb Iy ti me and
inc lude a CAL initiated monitor call that contains the logical device number as one of the arguments.
At execution time, monitor calls are processed by the CAL Handler within the monitor.
Non-I/O functions are then further processed by the Monitor Control routine, and I/o functions are
processed by the I/o Control routine (see Figures 2-2 and 2-3). A complete description of each of
these commands is given in Chapter 3. If the original command involved is an I/o function, the I/o
control routine checks the Device Assignment Table to associate the logical I/o device (specified by
the system macro) to a physical I/o device. In the I/o Monitor environment, the logical/physical
device associations can be modified only by reassembly. In the Keyboard and Background/Foreground
Monitor environments, device associations can be modified at System Generation time, or by means of
the ASSIG N keyboard command just pri or to loadi ng a system or user program. This capabi lity adds
true device independence to the monitor systems.

Function
Code

Command
.INIT

Functions processed
by I/o control routine

Functions processed by
monitor control routine

Figure 2-3

.DLETE, .RENAM, and .FSTAT

.SEEK

.ENTER

.CLEAR

.CLOSE

.MTAPE

• READ and .REALR

.WRITE and .REALW

.WAIT and .WAITR

.TRAN

• TIMER

• EXIT

.SETUP

.IDLE

Monitor Commands and Function Codes

2-4

NOTE
.INIT, .READ, .WRITE, .WAIT, .WAITR, .CLOSE,
• TIMER, and .EXIT are recognized by all three monitors •
•SEEK, .ENTER, .FSTAT, .RENAM, .DLETE, • TRAN,
.CLEAR, and .MTAPE are recognized by the Keyboard
and Background/Foreground Monitors (and are ignored
by the I/O Monitor) •
•SETUP is used by the Monitors in setting up the I/o
skip chain and API channel registers (see Chapter 7) •
•ID LE is recogni zed by the Background/Foreground
Monitor only.

When the logical/physical I/O device association has been established, the monitor passes
control to the appropriate I/o device handler which initializes itself, initiates I/o, and returns control
to the system or user program. As mentioned previously, the system or user program retains control unti I
the specified device causes an interrupt (PI or API). At this point, it relinquishes control to the device
handler to continue or complete the specified I/O operation. In either case, control is returned to the
system or user program at the point where it was interrupted. The system or user program, by means of
a . WAIT system macro (described in Chapter 3), can determi ne whether an input or output operati on
has been completed. If the transfer of data from or to the system or user program line buffer has been
completed, program execution continues; if the transfer has not been completed, control is returned to
the •WAIT macro.
Additional buffering is provided by the individual device handlers as required. All device
handlers are non-resident in the sense that only those handlers required by the system or user program
are loaded into core.

2.2

LINE BUFFERS
As menti oned in the preceedi ng genera I descri pti on of the moni tor envi ronment, each system

or user program must internally set up line buffers to be used in transmitting data to or from the external
environment. An exception to this rule is when data is transmitted in the Dump mode (described in
Section 2.3.3). Each line buffer ofn words (always even) should be set up to consist ofa two-word
header (termed a header word pair) followed by n-2 words of data as shown in Figure 2-4.

2-5

Word 0

First Word of Line Buffer Header

Word 1

Second Word of Li ne Buffer Header

Word 2

First Word of Data Area

Last Word of Data Area

Word n-1

FiglJ"e 2-4

Li ne Buffer Structure

A system or user program should contain at least one line buffer for each device that is to
be used. This buffer is used to set up output lines before transmittal to an output device, or to receive
input lines from the associated input device. The monitor accepts commands (system macros) from
system or user programs to initiate input to the line buffers and to write out the contents of line buffers.
Complete descriptions of these commands are given in Chapter 3. Line buffers are internal to, and
must be defined by, each system or user program. The header word pair within a line buffer is detai led
in Figure 2-5. The .BLOCK pseudo operation may be used to reserve space for a line buffer. A tag
is required to allow referencing by indivdual .READ and .WRITE macros. For example:
.DEC
LINEIN

.BLOCK 52

UNOUT

.BLOCK 52

/creates 52-word line
/buffer named UNEIN.
/creates 52-word line
/buffer named UNOUT.

Before output, the user must set the appropriate word pair count in bits 1 through 8 of word
zero in the line buffer if they have not a Iready been set by a device handler on input. This count
overrides the word count passed to lOPS by the. WRITE macro. (The word count must still be specified
in the .WRITE macro for each data mode; however, it only has meaning in Dump mode since there is
no header word pair.) In lOPS binary mode (discussed in Paragraph 2.3.1 .2), bits 9 through 11 should
be set to 101 if the output wi II ultimately be on cards. The checksum word, the second word in the
header, need not be set by the user since checksums are computed by lOPS.
Before input, the user should not be concerned with the header word pair since they wi II be
set by lOPS to enable the user to determine what has happened after input has terminated.
On input, the word count specified in the .READ macro is used by lOPS to determine the
maximum number of locations to be occupied by the data being read. If the word count is exceeded
before input is terminated, or if there is a parity or checksum error, lOPS sets the appropriate va lidity
bits in header word 0 to i ndi cate the error.

2-6

o
COUNT

IGNORE CHECK SUM
ON BINARY INPUT

9--11

~~B

, 13
V
1

17
lID MODE

FOR lOPS BINARY ONLY
}
(CORRESPONDS TO 7-9 PUNCH
ON BINARY CARDS)

~~~~~~~~~~~~~~---'

VALIDITY BITS.
00 = DATA CORRECT
01
PARITY ERROR

10
CHECK SUM ERROR }
11 = SHORT LINE
.
(BUFFER OVERFLOW)

~~~~~~~~---'

lID MODE.
0000 = lOPS BINARY
0001 = IMAGE BINARY
0010= lOPS ASCII
001 1 • IMAGE ALPHANUMERIC

=
=

0100
DUMP
0101
EOF (LOGICAL!
011 0 = EOM (PHYSICAL!

* *}

~~~~~~~~~~---'

011 1 = TAPE LABEL"

* lOPS AND IMAGE MODES ONLY
0~~~~~~~~~~~~~~~~~~~~~~~~~---17

HEADER,
WORDI
~----------'----y~--~~--------~

CHECK SUM:
TWO'S COMPLEMENT OF HEADER WORD 0 PLUS
WORDS (0= CHECK SUM NOT COMPUTED)

Figure 2-5

DATA - - - - - - - '

Format of Header Word Pair

After input, the user should check the validity bits in word 0 of the line buffer header to
determine if the data was read without error. If multiple errors are detected, priority is given to a
parity error over a checksum error. lOPS ignores checksum errors on binary input if bit 0 of word 0
of the line buffer header is set to 1. lOPS sets the I/O mode bits (bits 14 through 17 of word 0 of the
line buffer header) to: 6 (0110 2 ) if it senses a physical end-of-medium (such as end-of-tape in the
paper-tape reader), or 5(0101 2 ) if it senses a logical end-of-file during an lOPS binary read.
When choosing a word count (that is, the maximum line buffer size) to specify in system
macros, both the set of possible devices and the mode of data transmission must be considered. The maximum line buffer sizes (including 2-word header) for standard peripheral devices, along with applicable
data modes, are listed in Table 2-1.

2-7

Table 2-1
Maximum Line Buffer Sizes

Maximum Line
Data Modes*
Buffer Size

Device
PR (paper tape reader)

52 10

All

34 10 sufficient if A mode only,
Heaaers accepted for B; generated
for A, I, H

PP (paper tape punch)

52 10

All

3410 sufficient if A mode only,
Headers output for B on Iy ,

TT (Teletype)

34 10

A,H only

A Ilows for 80 10 characters,
Headers generated on input,
Headers not output on output,

CD (card reader)

52 10

All

52
for B mode; 82 10 for I, H
mo es, Headers accepted for B;
generated for A, I, H,

LP (I i ne pri nter)

52 10

A only

Allows for 125 10 characters, No
headers output,

DTO-7 (DECtape)

255 10

All

MTO-7(magnetic tape)

255 10

All

OK (disk)

255 10

All

DR (drum)

255 10

All

* Data Modes are:

2,3

Notes

lOPS and image modes allow for
severa I Ii ne buffers (I og ica I records) per physica I block,

A = lOPS ASCII
B = lOPS Binary
0= Dump Mode
I = I mage Bi nary
H = Image Alphanumeric

DATA MODES
The Input/Output Programming System allows data transmission to or from a system or user

program in five different modes,
Mode
lOPS Binary
I mage Bi nary
lOPS ASCII
Image Alphanumeric
Dump

Code *

o
1
2
3

2-8

* Bits 14 through 17 of Header Word 0,
specified by system macro and set by lOPS,

2.3.1

lOPS Modes
The two lOPS data modes include lOPS ASCII and lOPS binary as shown in Figure 2-6 on

paper tape, and described in the following paragraphs.

TAPE CHANNEL
87654
321
FEED

DIRECTION)
OF TAPE
MOVEMENT

00000

000 0

000

00000 a

000

000
0

t'-___

L ._ _ _ _ _ _ _

7-BIT ASCII CODE
PARITY BIT IEVEN PARITY)

lOPS ASCII
TAPE CHANNEL
8765432
FEED

DIRECTION)
OF TAPE
MOVEMENT

.0000

0000

•

.0000

1st

6-BlTBYTE

2 nd 6-81 T BYTE

3 rd 6-81T BYTE

000

'--y-----J

t
~

6-BITS OF BINARY WORD
PARITY BIT 1000 PARITY)
MUST ALWAYS BE PUNCHED

lOPS BINARY

Figure 2-6

2.3.1.1

lOPS Mode Data on Paper Tape

lOPS ASCII - 7-bit ASCII is used by lOPS to accommodate the entire 128-character revised

ASCII set (Appendix A). All alphanumeric data, whatever its original form on input (ASCII, Hollerith,
etc.) or fi na I form on output, is converted i nterna Ily and stored as 5/7 ASCII. "5/7 ASCII" refers to
the internal packing and storage scheme. Five 7-bit ASCII characters are packed in two contiguous
locations as shown in Figure 2-7 and can be stored as binary data on any bulk storage device. Input
requests involving lOPS ASCII should be made with an even word count to accommodate the paired input.
ASCII data is input to or output from lOPS ordinarily, via the Teletype or paper tape, although it may exist in 5/7 ASCII form on any mass storage device. lOPS ASCII is defined as a 7-bit
ASCII character with even parity in the eighth (high order) bit, in keeping with USA standards. lOPS
performs a parity check on input of lOPS ASCII data prior to the 5/7 packing. On output, lOPS
generates the correct pari ty .

2-9

o .....f - - - - - - - -... 6

7 ......f - - - - - - -__•• 13

14 ...- -... 17

1ST CHARACTER

2ND CHARACTER

3RD CHARACTER
1-4

WORD 0

0_2
WORD 1

5TH CHARACTER

4TH CHARACTER

Figure 2-7

10"

47- UNUSED

5/7 ASCII Packing Scheme

Non-parity lOPS ASCII occurs in data originating at a Model 33, 35, or 37 Teletype, without the parity option. This data always appears with the eighth (high order) bit set to 1. Apart from
parity checking, the lOPS routines handle lOPS ASCII and non-parity lOPS ASCII data identically.
An alphanumeric line consists of an initial form control character (line feed, vertical tab,
or form feed), the body of the line, and a carriage return (CR) or ALT MODE. CR (or ALT MODE) is
a required line terminator in lOPS ASCII mode. Control character scanning is performed by some
device handlers for editing or control purposes (see Section 7.4 for effects of control characters on
specific devices).

2.3.1.2

lOPS Binary - lOPS Binary data is blocked in an even number of words, with each block

preceded by a two-word header. On paper tape (see Figure 2-6), lOPS binary uses six bits per frame,
with the eighth channel always set to 1, and the seventh channel containing the parity bit (odd parity)
for channels 1 through 6 and channel 8. The parity feature supplements the checksumming as a data
validity provision in paper tape lOPS binary.

2.3.2

Image Modes
Image Mode data is read, written, and stored in the bi nary or a Iphanumeri c form of the

source or terminal device, one character per word, as shown in Figures 2-8 and 2-9. No conversion,
checking, or packing is permitted, and character scanning is generally omitted.

2.3.3

Dump Mode
Dump Mode data is a Iways binary. Dump mode is used to output from or load directly into

any core memory area, bypassing the use of line buffers. Each dump mode statement has arguments
defi ni ng the core memory area to be dumped. Dump mode is norma Ily used wi th bu Ik storage devi ces,
although it is also possible to use it with paper tape output and input.

2-10

TAPE CHANNEL
87654
321
FEED
00000

000

000000000

DIRECTION)
OF TAPE
MOVEMENT

00000

000

~---y~---

ALL EIGHT CHANNELS USED

I MAGE ALPHANUMERIC

TAPE CHANNEL
87654

321

FEED

DIRECTION)
OF TAPE
MOVEMENT

.0000

000

.0000

000

.00000000

.0000

000

6-BIT BINARY CODE
(3 FRAMES/WORD)
IGNORED
MUST ALWAYS BE PUNCHED
IMAGE BINARY

Figure 2-8 Image Mode Data on Paper Tape

I
A

rsI
I

WORD COUNT

HEADER
WORD PAIR

WORD COUNT

.1-<
A

ABC;
INS/7ASCII

B
C

IMAGE ALPHANUMERIC

lOPS ASCII

2.3.4

ABC"
FO UR 8-B I T
CHARACTERS
>- (RIGHT
JUSTIFIED)

;

Figure 2-9

HEADER
WORD PAIR

lOPS ASCII and Image Alphanumeric
Data in line Buffers

Input/Output Data Mode Terminators
Input/output terminators for each of the data modes are summarized in Table 2-2.

2-11

Table 2-2
Input/Output Data Mode Terminators

I
N
P
U
T

lOPS
ASCII

lOPS
Binary

Image
Alphanumeric

Image
Binary

Dump

Carriage Return

Word Pair Count

Word Count

ALT MODE

End of Medium

Word Pair Count**

Word Count*

End of File**

End of Fi le~*

End of Fi le**

End of Medium

End of File**

Word Count*
End of Fi le**

0
U
T
P
U
T

Carriage Return
ALT MODE

Word Count
Word Pair Count

Word Pair Count***
(except on Teletype)

Word Pair Count

*A short Line Indicator will be placed by lOPS into the validity bits (12 and 13) of Header Word 0
if the maximum size of the line buffer is reached before an End-of-File.
**Bulk storage only.
***If the word pair count is not greater than 1, the output line is ignored. If the word pair count is
greater than 1, it has no effect and a carriage return or ALT MODE are the only legal line terminators.
2.4

SYSTEM TABLES
System tables used by each of the monitor systems include the Device Assignment Table

(.DAT), and the System Communication Table (.SCOM). These tables are discussed in the following
paragraphs.
2.4.1

Device Assignment Table (.DA T)
Both FORTRAN IV and MACRO-9 coded user programs, as well as the system programs,

specify I/o operations with commands to logica I I/o devices. One of the monitor's functions is to
relate these logical units to physical devices. To do this, each of the monitors contains a Device
Assignment Table (.DAT) which has "slot" numbers that correspond directly to logical I/o device
numbers. Each .DAT slot contains the physical device unit number (if applicable) along with a pointer
to the appropriate device handler.
All I/o communication in the monitor environment is accomplished by the logical/physical
device associations provided by the Device Assignment Table. The use of the Device Assignment Table
differs for each of the monitor systems, and is discussed separately for each of the monitors (Chapters 4,
5, and 6).

2-12

2.4.2

System Communication Table (.SCOM)
The System Communication Table (. SCOM) provides a list of registers that can be referenced

by the monitor, lOPS, and system programs. A complete list of . SCOM entries, and the purpose of
each, is given in Table 2-3. The System Communication Table begins at location 1008 .

Table 2-3
System Communication Table (.SCOM) Entries
Word

Purpose

.SCOM

First free register below resident portion of System Bootstrap (constant)

.SCOM + 1

First free register above resident KM-9 (constant)

.SCOM + 2

First free reg ister

.SCOM + 3

Last free register

.SCOM + 4

Hardware options available:
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6

1 = API
1 = EAE
1 = TTY is 35/37
1 = Non-resident KM-9 in core
1 = VC38 Character Table
1 = 339 Pushdown Table
1 = 9-channel, 0 = 7-channel Magnetic tape

Bits 15-17 Drum Size:
1 = 32K (RM09 A)
2 = 65K (RM09B)
3 = 131K (RM09C)
4 = 262K (RM09D)
5 = 524K (RM09E)
.SCOM + 5

System program starting location

.SCOM + 6

User starting location (bits 3 through 17), and:
Bit 0
Bit 1
Bit 2

1 = DDT Load
1 = G Load
1 = No-symbol-table Load

.SCOM + 7-11 8

Device numbers of Linking Loader1s devices. These are used to avoid
loading user handlers already in core for the Loader itself.

. SCOM + 12-158

Transfer vectors associated with API software level channel registers
40 through 43 8 .

. SCOM + 16

Conta i ns PC on keyboard interrupts •

. SCOM + 17

Conta i ns AC on keyboard interrupts .

2-13

2.5

SPECIFYING DEVICES USED TO LINKING LOADER
When writing a MACRO-9 program that uses monitor commands {system macros}, it is

necessary to use the .IODEV pseudo operation somewhere in the program to specify to the Linking
Loader which .DAT slots are to be used. The .IODEV pseudo-op causes a code to be generated that
is recognized by the Linking Loader and used to load device handlers associated with specified .DAT
slots. FORTRAN IV programs cause the compi ler to generate this code based on the units specified in
READ and WRITE statements. {If a variable is used in a FORTRAN program to specify an I/o unit,
handlers will be loaded for all positive .DAT slots that have handlers assigned.} The .IODEV pseudoop has the following form
.IODEV 3, 5, 6
where the MACRO-9 program containing this statement can use .DAT slots 3, 5, and 6. An error
message is generated if a slot called for by a program is unassigned.

2-14

CHAPTER 3
USER PROGRAM COMMANDS (SYSTEM MACROS)

All user program commands or system macros are described in this chapter for convenient
reference.

All commands that apply to the I/o Monitor are presented first and are followed by de-

scriptions of the additional commands that apply to the Keyboard and Background/Foreground Monitors,
respectively.

Because of the upward compatibility of monitor systems, all I/o Monitor commands (sys-

tem macros) are also used in the Keyboard and Background/Foreground Monitor environments.

All Key-

board Monitor commands (system macros) are also used in the Background/Foreground Monitor environment.

Note that all information presented in this manual for the Background/Foreground Monitor is

preliminary and subject to change.

NOTE
When executing a system macro, the monitor makes no
attempt to save the user's accumulator and link bit.

3.1

I/o MONITOR COMMANDS (SYSTEM MACROS)
The following commands are available for use in programs that are to operate in the I/o

Monitor environment.

Each command is described in detail in the paragraphs that follow.

Name

Purpose

. INIT

Initializes the device and device handler .

. READ

Transfers data from the device to the line buffer .

• WRITE

Transfers data from the line buffer to the device .

. WAIT

Checks availability of the user's line buffer and
waits if busy.

.WAITR

Checks availability of the user's line buffer, and
provides transfer address for busy return.

. CLOSE

Terminates use of a file •

. TIMER

Calls and uses real-time clock .

. EXIT

Returns control to the Monitor .

3-1

3. 1 . 1

.INIT {Initialize}

FORM:

.INIT

a, F, R

VARIABLES:

a = Device Assignment Table (. DAT) slot number (in octal radix)
F= File Type: {

0= Input File
1 = Output File

R = User Restart Address* (should be in every .INIT statement)
EXPANSION:

LaC

CAL + F7 - 8 + a 9 - 17

LaC + 1

LaC + 2

LaC + 3

/The CAL handler will place the unit number (if
/applicable) associated with. DAT slot a into bits
/0 through 2 of this word. **

/Maximum size of line buffer associated with. DAT
/slot ~, for example, 255 10 for DECtape. ***

DESCRIPTION: The macro .INIT causes the device and device handler associated with. DAT slot a to
be initialized •• INIT must be given prior to any I/O commands referencing .DAT slot~; a separate
.INIT command must be given for each .DAT slot referenced by the program. Each initialized .DAT
slot constitutes an open file to the device handler and must be .CLOSEd. Since a • DAT slot may refer
to only one type of file (input or output), only one file type specification (0 or 1) may be made in an
.INIT statement. If a . DAT slot first references an input file, then an output file (or vice versa), a
second .INIT command must be executed to change the transfer direction prior to the actual data transfer command.

3.1.2

.READ

FORM:

.READ

a, M, L, W

VARIABLES:

a = • DAT slot number (octal radix)

o = lOPS Binary
M = Data mode

1 = Image Binary
2 = lOPS ASCII
3 = Image Alphanumeric
4 = Dump Mode

*Has meaning only for .INIT commands referencing slots used by Teletype (the last .INIT command encountered for any slot referencing the keyboard or teleprinter takes precedence). When the user types
tP, control is transferred to R. For example, the Linking Loader takes advantage of this feature to restart the system when a new medium has been placed in the input device.
**Has no direct effect upon the user's program, but should be noted so that no attempt will be made to
use LaC + 1 as a constant.
***Size is returned by the handler so that the program, in a device-independent environment, can use
it to properly set up line buffers.

3-2

L = Line Buffer address
W = Line buffer word count (decimal radix), including the two-word header
EXPANSION:

LaC

CAL + M6 - 8 + 9-17

LaC + 1

LOC + 2

L
. DEC

LOC + 3

/CAL Handler will place unit number (if applicable)
/into bits through 2.

/Decimal radix

-W

DESCRIPTION: The . READ command is used to transfer the next I ine of data from the device assigned
to. DAT slot ~ to the line buffer in the user's program. In the operation, M defines the mode of the
data to be transferred; L is the address of the line buffer; and W is the number of words in the line buffer
(including the two-word header).
Since I/O operations and internal data transfers may proceed asynchronously with computat ion, a . WAIT command must be used after a • READ command before the user attempts to use the data
in the line buffer or to read another line into it.
When a . READ (non-dump mode) has been completed, the program should interrogate bits
12 through 13 of the first word of the line buffer header to ascertain that the line was read without
error. Bits 14 through 17 should be checked for end-of-medium and end-of-file conditions.

3.1.3

.WRITE

FORM:

.WRITE

a, M, L, W

VARIABLES:

a = . DAT slot number (octal radix)

a = lOPS Binary
M = Data mode

1 = Image Binary
2 = lOPS ASCII;-';'
3 = Image Alphanumeric
4 = Dump Mode

L = Li ne buffer address
W = Line buffer word count (decimal radix), including the two-word header
EXPANSION:

LaC

CAL + M6 - 8 to a9_ 17

LaC + 1

LaC + 2

L
. DEC

LaC + 3

/CAL Handler will place the unit number (if appli/cable) associated with. DAT slot a into bits
/0 through 2.

/Decimal radix

-W

3-3

DESCRIPTION: .WRITE is used to transfer a line of data from the user's line buffer to the device
associated with. DAT slot E1, •
•WAIT must be used after a .WRITE command, before the line buffer is used again, to insure
that the transfer to the device has been completed.
On non-bulk storage devices, headers are output along with the data in lOPS binary mode
only (bit 9 and 11 of header word 0 should be set to 1). On bulk storage devices, headers are output
along with the data in all modes except dump mode. In image modes, the header space cannot be
used for data, even though the headers are not written out. The word pair count in the header takes
precedence over maximum size (or word count) in all modes and must be inserted by the user.
For both .READ and .WRITE macros, dump mode causes the transfer of the specified core
area to or from one record on magnetic or paper tape. One or more blocks on DECtape or disk may be
occupied by a single dump command. A subsequent .WRITE in dump mode will utilize the unfilled
portion of the last block •

3.1.4

•WAIT

FORM:

.WAIT

VARIABLES:

a = • DAT slof number (octal radix)

EXPANSION:

LOC

CAL + a9-17

LOC + 1

/The CAL Handler will place the unit number (if
/applicable) associated with. DAT slot a into bits
/0 through 2.

DESCRIPTION: .WAIT is used to detect the availability of the user's line buffer (being filled by .READ
or emptied by .WRITE). If the line buffer is available, control is returned to the user immediately after
the. WAIT macro expansion (LOC + 2). If the transfer of data has not been completed, control is returned to the • WAIT macro.

3.1.5

. WAIT must a Iso be used after the . TRAN command •

•WAITR

FORM:

•WAITR

a, ADDR

VARIABLES:

a = • DAT slot number (octal radix)
ADDR = Address to which control is passed if line buffer is not available for use.

EXPANSION:

LOC

CAL + 10008 + a9-17

LOC + 1

LOC +2

ADDR

/The CAL Handler will place the unit number (if
/applicable) associated with. DAT slot a into bits
/ 0 through 2.

3-4

DESCRIPTION: .WAITR is also used to detect the availability of the user's line buffer. If the buffer
is avai lable, control is returned to the user immediately after the • WAITR macro expansion (LOC + 3).

If the transfer of the data has not been completed however, control is given to the instruction at ADDR.
It is the user's responsibility to return to the .WAITR to again check the availability of the buffer •

3. 1 .6

• CLOSE

FORM:

.CLOSE

VARIABLES:

a = . DAT slot number (octal radix)

EXPANSION:

LOC

CAL + a9-17

LOC + 1

/The CAL Handler will place the unit (if applicable)
/associated with. DAT slot ~ into bits 0 through 2.

DESCRIPTION: When action has been initiated (.INIT or . SEEK or • ENTER) on a file (whether the
device is file-oriented or not) this action must be terminated by a .CLOSE command.
On input, it is assumed that the user is finished with the file when the .CLOSE macro is
used, so the file is closed. On output, all associated output is allowed to finish and then an EOF (endof-file) line is output before the file is finally closed. If ~ refers to a file-oriented device, any earlier
fi Ie of the same name and extension, as currently referenced, is deleted from its directory after the
new fi Ie is written.

3.1.7

. TIMER
n,C

FORM:

• TIMER

VARIABLES:

n = Number of clock increments (decimal radix)
C = Address of subroutine to handle interrupt at end of interval

EXPANSION:

LOC

CAL

LOC + 1

LOC + 2

C
. DEC

LOC + 3

/Decimal radix

-n

DESCRIPTION: • TIMER is used to set the real-time clock to n increments and to start it.

Each clock

increment represents 1/60s for 60 Hz systems and 1/50s for 50 Hz systems.
C + 1 is the location to which control is given when the Monitor services the clock interrupt.
The coding at C should be in subroutine form; for example,

3-5

/C + 1 is reached via JMS

DAC SAVEAC
: } Must not contain any Monitor CALs
•
in I/O or Keyboard Systems.
LAC C

/Restore Link

RAL
LAC SAVEAC
XIT

/Restore AC

JMP* C

so that control will return to the originally-interrupted sequence when the interval-handling routine
has been completed. The Monitor automatically reenables the interrupt system before transferring control to C + 1. If the user wishes to initiate another interval at the completion of the previous interval
in the subroutine specified to • TIMER, he may do so as follows:
LAC

(desired interval in 2's complement)

DAC* (7
/Restore Li nk

LAC C
RAL
LAC SAVEAC

/Restore AC

CLON

/Turn on clock

JMP* C

3.1.8

. EXIT

FORM:

• EXIT

EXPANSION:

LOC

CAL

LOC + 1

DESCRIPTION: • EXIT provides the standard method for returning to the Monitor after completion of a
system or user program. In the I/O Monitor environment, it causes a program halt; in the Keyboard
Monitor environment, it causes the non-resident monitor to be reloaded. When the reloading process
has been completed, the Monitor types
MONITOR

$
on the teleprinter, indicating that it is ready to accept the next command. In the Background/Foreground Monitor environment, the effect of the. EXIT depends upon whether it occurs in a BACKGROUND
or a FOREGROUND job (see Section 6.4.5).

3-6

3.2

KEYBOARD MONITOR COMMANDS (SYSTEM MACROS)
The commands listed below are available for use in programs that are to operate in the Key-

board Monitor environment.

Each command is described in detail in the following paragraphs.

Refer

to Chapter 5 for a complete description of bulk storage file organization.
Name

Purpose

.SEEK

Locates file on file-oriented device and begins data input.

· ENTER

Primes file-oriented device for output.

· FSTAT

Checks presence of fi Ie on fi Ie-oriented device.

• RENAM

Renames fi Ie on fi Ie-oriented device •

• DLETE

Deletes fi Ie from fi Ie-oriented device.

.TRAN

Reads or records user-specified block on bulk storage devices,
providing the user with the capability to determine the structure
of the fi les on the device.

. Cl EAR

Initializes file structure on file-oriented device •

• MTAPE

Provides special commands for IBM-compatible magnetic tape •

The first se~en of the eiQht macros Iisted above apply to the fi Ie-oriented devices - DECtape
(DT), disk (DK), drum (DR) and magnetic tape (MT); they are ignored by nonfile-oriented devices, depending upon the device handler used. The eighth macro, .MTAPE, handles the nonfile-oriented functions of magnetic tape (REWIND, BACKSPACE, etc.). If these nonfile-oriented commands are given to
file-oriented devices, they are ignored by the device handling routines. To the the .MTAPE commands,
however, (REWIND TO LOAD POINT, BACKSPACE RECORD), may be used with disk drum or DECtape;
when so used, they preclude the use of .SEEK or • ENTER (see Section 5.6).

3.2.1

.SEEK

FORM

.SEEK a ,D

VARIABLES:

a == .DAT slot number (octal radix)
D == Address of user directory entry block

EXPANSION:

DESCRIPTION:

LOC

CAL + a 9- 17

LOC + 1

LOC + 2

/The CAL Handler will place unit number (if appli/cable) into bits 0 through 2.

.SEEK is used to search the directory of file-oriented device ~ for a desired file and to

begin input for subsequent .READ commands. D is a pointer to (that is, the address of) a three-word
entry in the user's program containing the file name and extension information. The device IS file
directory block is searched for a matching entry and if found, input of the file into the handler's internal

3-7

buffer begins. If no matching entry is found, control is transferred to an error-handling routine in the
Monitor, an error message is printed on the teleprinter and the Monitor resumes control.

Execution of

the • FSTAT command allows the user to check the directory for a named file and to retain control if
not found.
The entry format in the user's file directory entry block (in core) is as follows:

5 6

11 12

D+1

D+2

File Name: up to six 6-bit trimmed
ASCII characters, padded, if necessary, with nulls (0).
Fi Ie Name Extension: Up to three 6bit trimmed ASCII characters, padded
with nulls. (The symbol @ produces a
zero when using SIXBT.)

The fi Ie name is essentially nine characters (six of fi Ie name and three of fi Ie name extension); the file-searching of the .SEEK command takes into account all nine characters.
System programs use predetermined fi lename extensions in their operation. For example, if
FORTRAN IV or MACRO-9 wishes to • SEEK program ABCDEF as source input, it searches for ABCDEF
SRC (ABCDEF, Source). The binary output produced would be named ABCDEF BIN (ABCDEF, Relocatable Binary), while the listings produced would be named ABCDEF LST (ABCDEF, Listing). The
Linking Loader, if told to load ABCDEF, would. SEEK ABCDEF BIN.

3.2.2

• ENTER

FORM:

. ENTER

a, D

VARIABLES:

a = .DAT slot number (octal radix)
D = Address of user directory entry block

EXPANSION:

LOC

CAL + a9-17

LOC + 1

LaC + 2

/The CAL Handler will place the unit number (if
/applicable) associated with. DAT slot a into
/bits 0 through 2.

DESCRIPTION: . ENTER is used to examine the directory of the device referenced by • DAT slot ~ to
find a free four-word directory entry block in which to place the three-word block at D and one word
of retrieval information when. CLOSE is later issued.

Deletion of any earl ier fi Ie with the same name

and extension is performed by the .CLOSE macro. Control is transferred to the error handling routine
in the Monitor to output an appropriate error message if there is no avai lable space in the fi Ie directory
at the time when • ENTER is executed.

3-8

3.2.3

• FSTAT

FORM:

.FSTAT

a, D

VARIABLES:

a = . DAT slot number (octal radix)
D = Starting address of three-word block of storage in user area containing
the file name and extension of the file whose presence on the device
associated with. DAT slot a is to be examined.

EXPANSION:

LOC

CAL + 3000 + a9-17

LOC + 1

LOC + 2

/The CAL Handler will place the unit number
/associated with. DAT slot a into bits 0 through 2
/of LOC + 1.
-

DESCRIPTION: . FSTAT checks the status of the file specified by the file entry block at D on the device associated with. DAT slot a. On return, the AC will contain the first block number of the file
if found. The contents of the AC wi II be zero on return, if the specified fi Ie is not on the device. It
is recommended that. FST AT be used prior to . SE EK, if the user prefers to retain program control when
a fi Ie is not found in the directory. Otherwise, control is returned to the Monitor error routine to out-.
put an lOPS 13 error code on the Teletype.

3.2.4

.RENAM

FORM:

.RENAM

a,D

VARIABLES:

a = . DAT slot number (octal radix)
D = Starting address of two 3-word blocks of storage in user area containing
the fi Ie names and extensions of the fi Ie to be renamed and the new
name, respectively.

EXPANSION:

LOC

CAL + 2000 + a9-17

LOC + 1

LOC + 2

/The CAL Handler will place the unit number
/associated with. DAT slot a into bits 0 through 2
/of LOC + 1.
-

*Bits 0 through 2 of LOC + 2 must be set to zero prior to the execution of the CAL at LOC. On return,
bits 0 through 2 of LOC + 2 will contain a code indicating the type of device associated with. DAT
slot a.
0= Non-fi Ie-oriented devices
1 = DECtape (2 through 7 to be specified)

If the contents of the AC are 0 on return from . FSTAT (indicating that the file was not found), bits 0
through 2 of LOC + 2 should be checked because if they are still 0, the device was non-file-oriented.

3-9

DESCRIPTION: . RENAM renames the file specified by the file entry block at D with the name in the
file entry block at D + 3 on the device associated with. DAT slot~. The contents of the AC will be
zero on return, if the file specified at D cannot be found.

3.2.5

• DLETE

FORM:

• DLETE

VARIABLES:

a = • DAT slot number {octal radix}

a, D

D = Starting address of three-word block of storage in user area containing
the file name and extension of the file to be deleted from the device
associated with .DAT slot a.
EXPANSION:

LOC

CAL + 1000 + a9-17

LOC + 1

LOC + 2

/The CAL Handler will place the unit number
/associated with. DAT slot a into bits 0 through 2
/of LOC + 1.
-

DESCRIPTION: • DLETE deletes the file specified by the file entry block at D from the device associated
with. DAT slot ~ and retrieves the storage blocks released by that file. The contents of the AC will be

o on return if the specified file cannot be found •
3.2.6

• TRAN

FORM:

.TRAN

a, D, B, L, W

VARIABLES:

a = • DAT slot number (octal radix)
D = Transfer direction
Input Forward =:(Q)
Output Forward = 1
*Input Reverse ~. ,
*Output Reverse =~,,)
B = Device address for example, block number (octal radix) for DECtape
L = Core starting address
W = Word count (decimal radix)

EXPANSION:

LOC

CAL + D7-8 + a9-17

LOC + 1

LOC + 2

/The CAL Handler will place the unit number (if
/applicable) associated with. DAT slot a into bits
/0 through 2.
-

*DECtape only.

3-10

LaC + 3

L
.DEC

LaC + 4

/Decimal radix

-W

DESCRIPTION: • TRAN is employed when the user desires total freedom in data structuring of bulk
storage devices. It provides the facility to read or record user-specified areas on the device •• TRAN
should be followed by a • WAIT macro to ensure that the transfer has been completed.

3.2.7

.CLEAR

FORM:

.CLEAR

VARIABLES:

a = • DAT slot number (octal radix)

EXPANSION:

LaC

CAL + a9-17

LaC + 1

/rhe CAL Handler will place the unit number (if
/applicable) associated with. DAT slot a into bits
/0 through 2.
-

DESCRIPTION: .CLEAR is used to initiate the lOPS file structuring of the device referenced by • DAT
slot ~ by initial izing its existing directory. The directory area and fi Ie bit map blocks on the filestructured device are set to 0 (except for those bits in the directory bit map referring to the directory
itself and the file bit maps).
In order to avoid clearing a directory when its files are still in use, the directory is checked
for open files. If there are no open files, the directory is cleared; otherwise, control is transferred to
the monitor error handling routine to output an lOPS 10 error code (file still active).

3.2.8

.MTAPE
a

,(x'X)

FORM:

• MT APE

VARIABLES:

a = • DAT slot number (octal radix)

~.,

XX = Number of magnetic tape function or configuration:
00 = Rewind to load point
02 = Backspace record
03 = Backspace fi Ie
04 = Write end-of-fi Ie
05 = Skip record
06 = Skip fi Ie
07 = Skip to logical end-of-tape
10 = 7-channel, even parity, 200 bpi
11 = 7-channel, even parity, 556 bpi
12 = 7-channel, even parity, 800 bpi
13 = 9-channel, even parity, 800 bpi
14 = 7-channel, odd parity, 200 bpi
15 = 7-channel, odd parity, 556 bpi
16 = 7-channel, odd parity, 800 bpi
17 = 9-channel, odd parity, 800 bpi

3-11

EXPANSION:

LOC

CAL + X?<S-8 + a9-17

LOC + 1

/The CAL Handler will place the unit number (if
/applicable) associated with. DAT slot a into bits
/0 through 2.
-

DESCRIPTION: .MTAPE is used to perform functions unique to non-file-oriented bulk storage devices.
In general, these functions are intended for magnetic tape; however, two of the functions, REWIND TO
LOAD POINT and BACKSPACE RECORD may be used with any bulk storage device that is to be employed in a non-file-oriented manner. For example, the DECtape Handler is directed to work in a
file-oriented mode for a particular .DAT slot if it encounters a .SEEK or . ENTER as the next command
after the .INIT command for that .DAT slot. If it encounters .MTAPE REWIND or BACKSPACE as the
first command after. INIT, it sets up to work in non-file-oriented modes and interprets subsequent .READ
and • WRITE commands appropriately. After the mode is establ ished, commands in the other mode must
not be executed.
3.3

BACKGROUND/FOREGROUND MONITOR COMMANDS (SYSTEM MACROS)
The following commands are available for use in programs that are to operate in the Back-

ground/Foreground Monitor environment.

Each command is described in detail in the paragraphs that

follow. It should be noted that this information is preliminary and subject to change.

Purpose

Name

3.3. 1

· REALR

Real time transfer of data from device to line buffer.

. REALW

Real time transfer of data from line buffer to device •

.IDLE

Allows FOREGROUND job to indicate that control can be given to lower
levels of the FOREGROUND job or to the BACKGROUND job.

.IDLEC

Allows FOREGROUND Mainstream to give control to BACKGROUND job
and subsequently continue processing after the. I DLEC.

• TIMER

Calls and uses real-time clock and allows priority level to be established.

.RLXIT

Accomplishes the exit from all real-time subroutines that were entered
via. REALR, • REALW or • TIMER requests.

• REALR

FORM:

.REALR

a, M, L, W, ADDR,p

VARIABLES:

a = • DAT s lot number (octa I radix)

M = Data mode

0= lOPS binary
1 = Image binary
2 = lOPS ASCII
3 = Image Alphanumeric
4 = Dump Mode

L = Li ne buffer address

3-12

W = Line buffer word count {decimal radix}, including the two-word header
AD DR = lS-bit address of closed subroutine that is given control when the
request made by the • REALR is completed.
p = API priority level at which to go, to ADDR
P

Priority Level

Mainstream
Level of • REALR
API software level S
API software level 6
API slftware level 7

4
S

6
7
EXPANSION:

LaC

CAL + 10000 + M6- 8 + a9-17

LaC + 1

LaC + 2

L
.DEC

LaC + 3

-W
.OCT

LaC +4

/Decimal radix

/Octal radix

AD DR + pOOOOO

DESCRIPTION: The .REALR command is used to transfer the next line of data from the device assigned
to • OAT slot ~ to the line buffer in the user's program. In this operation, M defines the mode of the
data to be transferred, L is the address of the line buffer, W is the number of words in the line buffer
{including the two-word header}, and ADDR is the address of a closed subroutine which should be constructed as shown in the following example.
ADDR

0
DAC
}

3.3.2
FORM:

SAVEAC

/Save AC

Any system macro may be issued
at this point.

LAC

SAVEAC

/Restore AC

.RLXIT

ADDR

/Return to interrupted point via monitor CAL **

.REALW
.REALW

a, M, L, W, ADDR, p

*The subroutine specified by a .REALR should not be used at more than one priority level. The subroutine is entered via a JMS and thus cannot be protected against re-entry.
** .RLXIT is described in Section 3.3.6.

3-13

VARIABLES:

a = • OAT slot number (octal radix)
0= lOPS binary
1 = Image binary
2 = lOPS ASCII
3 = Image Alphanumeric
4 = Dump Mode

M = Data mode

L = Li ne buffer address
W = Line buffer word count (decimal radix), including the two-word header
ADDR = 15-bit address closed subroutine that is given control when the request made by the .REALW is completed.
p = API priority level at which to go to AD DR
P

Priority Level

Mainstream
Level of • REALW
API software level 5
API software Ieve I 6
API software level 7

4
5
6
7
EXPANSION:

LOC

CAL + 10000 + M6-8 + a9-17

LOC + 1

LOC + 2

L
.DEC

LOC+ 3

-W
.OCT

LOC+4

IDecimal radix

10ctai radix

ADDR + pOOOOO

DESCRIPTION: The .REALW command is used to transfer the next line of data from the line buffer in
the user's program to the device assigned to .DAT slot~. In this operation, M defines the mode of the
data to be transferred, L is the address of the line buffer, W is the count of the number of words in the
line buffer (including the two-word header), and ADDR is the address of a closed subroutine which
should be constructed as shown in the following example.
EXAMPLE:
ADDR

0
DAC
}

SAVEAC

lSove AC

Any system macro may be
issued at this point.

LAC

SAVEAC

/Restore AC

.RLXlT

ADDR

/Return to interrupted point via Monitor CAL **

*The subroutine specified by a .REALW should not be used at more than one priority level. The subroutine is entered via a JMS and thus cannot be protected against re-entry.
** .RLXIT is described in Section 3.3.6.

3-14

3.3.3

.IDLE

FORM:

.IDLE

EXPANSION:

LOC

CAL

LOC +

DESCRIPTION: The FOREGROUND job in a Background/Foreground environment can indicate that
wishes to relinquish control to lower levels of the FOREGROUND job or to the BACKGROUND job by
executing this command. This is useful when the FOREGROUND job is waiting for the completion of
real-time I/o from anyone of a number of I/o requests that it has initiated or when it is waiting for
completion of •TIMER requests.
The .IDLE is the logical end of the current level IS processing; that is, control never returns
LOC + 2. If the .IDLE is issued at a FOREGROUND API software level, it effects a DBR from the
handler at that level. Other routines in the APIQ for that level are deferred until a hardware interrupt
is requested for that level again. If the .IDLE is issued at FOREGROUND mainstream, it effects an

I/o BUSY situation (except that no BUSY flag is set) and control goes to the BACKGROUND JOB. If
the .IDLE is issued at BACKGROUND mainstream level, it effects an I/o BUSY situation and control
is returned to the .IDLE CAL.

3.3.4

.IDLEC

FORM:

.IDLEC

EXPANSION:

LOC
LOC

CAL+1000
+ 1

DESCRIPTION: Identical to .IDLE except when issued at FOREGROUND mainstream level. In this
case, control goes to the BACKGROUND job, and LOC + 2 is saved as the FOREGROUND mainstream
return pointer. The next time control returns to FOREGROUND (at any priority level), FOREGROUND
mainstream processing will CONTINUE at LOC + 2 when mainstream becomes the highest active FOREGROUND level.
3.3.5

. TIMER

FORM:

.TIMER n, C, p

VARIABLES:

n = Number of clock increments (decimal radix)*
C = Address of subroutine to handle interrupt at end of interval **
p = API priority level at which to go to C

*To transfer control to subroutine C at priority level p immediately, n should be set equal to zero.
**The subroutine specified should not be used at more than one priority level. The subroutine is
entered via a JMS and thus cannot be protected against re-entry.

3-15

Prioritl Level

Mainstream
Level of • TIMER
API software level 5
API software level 6
API software level 7

4
5
6
7
EXPANSION:

LaC

CAL

LaC + 1

LaC +2

C + pOOOOO
.DEC

LaC + 3

/Decimal radix

-n

DESCRIPTION: • TIMER is used to set the real-time clock to n increments and to start it. Each clock
increment represents l/60s for 60 Hz systems and 1/50s for 50 Hz systems. When the monitor services
the clock interrupt, it passes control to location C + 1 with the priority level set to p. The coding at
C should be in subroutine form, for example,
C

0
DAC

SAVEAC

/C + 1 is reached via JMS

The restriction that applies to non B/F monitors does
not apply here. Any system macro (including. TIMER)
may be issued at this point.

LAC

SAVEAC

/Restore AC

.RLXIT

/Return to interrupted point via monitor CAL

so that control will return to the originally interrupted sequence when the interval-handling routine
has been completed. The Monitor automatically reenables the interrupt system before transferring
control to C + 1 •

3.3.6

• RLXIT

FORM:

.RLXIT

VARIABLES:

ADDR = entry point address of real-time subroutine that is to be exited.

EXPANSION:

LaC

CAL

LaC + 1

ADDR

DESCRIPTION: .RLXIT is used to exit from all real-time subroutines toot were entered via. REALR,
• REALW or • TIMER requests. The instruction just preceding the. RLXIT call should restore the AC with
the value of the AC on entrance to this subroutine •• RLXIT will restore the link from bit 0 of ADDR.

3-16

.RLXIT protects against re-entrance to BACKGROUND or FOREGROUND mainstream real-time subroutines. When the contents of ADDR is non-zero, the subroutine is assumed active; • RLXIT sets the
contents of ADDR to 0 thus making it available again. NOTE: Real-time subroutines should initially
have their entry point register set to O.

3-17

CHAPTER 4
INPUT/OUTPUT MONITOR

4.1

INPUT/OUTPUT MONITOR FUNCTIONS
The I/O Monitor of the PDP-9 ADVANCED Software System simplifies the programming of

input and output functions in the basic paper-tape environment. It serves as an interface between the
system and user programs and the external world of device hardware, relying upon the routines and
capabilities of the Input/Output Programming System (lOPS) to relieve the programmer of writing his
own device and data handling subroutines. The I/o Monitor allows simultaneous operation of many
I/o peripherals and overlapped computation. Since upward compatibility exists between the monitor
systems, user programs that are written to operate under control of the I/O Monitor will also operate
without modification, under control of the Keyboard and Background/Foreground Monitors.
The Input/Output Monitor is designed to take advantage of the Automatic Priority Interrupt
(API) if it is present on the system. Both the I/O skip chain for the Program Interrupt Control (PIC) and
the API channels are set up to handle all devices which have been requested by the user. All unused
channels are tied to an error routine to detect spurious interrupts.
The reader is referred to Chapter 2 for a general discussion of the monitor environment, and
to Chapter 3 for detailed descriptions of user program commands {system macros} available in the I/o
Monitor environment.

4.2

PROGRAMMING EXAMPLE
The following example illustrates the use of system macros with MACRO-9 programs in the

I/o Monitor environment. The example inputs a line of data from the Teletype keyboard, and outputs
the same line of data to the Teletype. The arguments used by the system macros are given symbolic
names (via MACRO-9 direct assignment statements) to faci litate recall for the programmer, and to
change the arguments easily, if desired.

Note the use of the pseudo ops .TITLE, .IODEV, .BLOCK,

and .END, in addition to the system macros. The assembly listing that follows the example shows how
the system macros are expanded at assembly time. (The reader may wish to compare these expansions
with the system macro descriptions in Chapter 3.)

• T iTl...t: ECHO

TIl =2
TTO=41f?l
OlJT=l
I N= 0

IOPS=2

4-1

START
BEGI~

RESTRT
BUFFER

• IODEV
• I NI T
• I NI T
.READ
• 'alA IT
.WRITE
• 'alAI T
JMP
.ClOSE
.CLOSE
JMP
.BlOCK
.END

2,4
TTO,OU:-,RESTRT
TTl, IN, RESTRT
TTI,IOPS,BUFFER,34
TTl
TTO,IOPS,BUFFER,34
TTO
BEGIN
TTl
TTO
START
42
START

IINITIALIZE TELETYPE OUTPUT
lAND IN?UT
IINPUT lOPS ASCII FROM TELETYPE
IWAIT UNTIL INPUT COMPLETE
10UTPUT SAME DATA ON TELETYPE
IWAIT UNTIL OUTPUT COMPLETE
IlOOP TO INPUT AGAIN
ITERMINATE INPUT
ITERMINATE OUTPUT
IRETURN TO REINITIAlIZE
ISET UP TElETYP~ BUFFER (34 DEC)
lEND OF ECHO PR01RAM

ASSEMBLY LISTING:

PAGE

ECHO

• TITLE
000007
000010
000001
000000
000002
00000
00000
00001
00002
00003

R
R
R
R
R

00004
00005
00006
00007
00010
00010
00011
00012

A
A
A
A
A
A-GEN*
A GEN*
R GEN*
A GEN*

R
R
R
R
R
R
R
R

000007
000001
000025
000000

A GEN*
A GEN*
R GEN*
A GEN*

00013

777736

A GEN*
A GEN*
R GEN*
GEN*
A GEN*

00014
00015

R
R

000007
000012

A GEN*
A GEN*

00016
00017
00020

R
R
R

002010
000011
000032

00021

777736

A GEN*
A GEN*
R GEN*
GEN*
A GEN*

00022
00023

000010
000012

A GEN*
A GEN*

.IODEV
2 .. 4
.INIT
TTO,OUT,RESTRT
CAL+OUT*1000 TTO&777
1
RESTRT
0
.INIT
TTI,IN,RESTRT
CAL+IN*1000 TTI&777
1
RESTRT

START
001010
000001
000025
000000

TTI,IOPS,BUFFER,34
.READ
CAL+IOPS*1000 TTI&777
10
BUFFER
.DEC
-34
.WAIT
TTl
CAL TTl&777
12
TTO,IOPS,BUFFER,34
• WR ITE
CAL+IOPS*1000 TTO&777
11
BUFFER
.DEC
-34
TTO
• WAIT
CAL TTO&777
12

BEGIN
002007
000010
000032

ECHO

TTI=2
TTO=4
OUT=1
IN=0
IOPS=2

4-2

00024
00025
00025
00026

R
R
R
R

00027
00030
00031
00032

R
R
R
R

600010

RESTRT
000007
000006

A GEN*
A GEN*

000010
000006
600000

A GEN*
A GEN*
R
A
BUFFER
R

000000

4.3

JMP
BEGIN
.CLOSE
TTl
CAL TTl&777
6
·CLOSE
TTO
CAL TTO&777
6
JMP
START
.BLOCK
42
.END
START
NO ERROR LINES

OPERATING THE I/O MONITOR SYSTEM
The reader is referred to the I/o Monitor Guide (DEC-9A-MIFA-D) for detailed operating

procedures for system programs in the I/O Monitor environment. The following PDP-9 ADVANCED
Software System manuals contain additional detailed information on system programs.
Manual

Document Number

Ut iii ty Programs

DEC-9 A-GUAB- D

MACRO-9 Assembler

DEC-9A-AMZA-D

FORTRAN IV

DEC-9A-KFZA-D

This section contains descriptions of loading programs, device assignments, and error detection and
handling.
4.3. 1

Loading Programs in the I/o Monitor Environment
In the paper tape system, each system program accompanied by the necessary I/O device

handlers and an appropriate version of the I/O Monitor, is punched on a separate paper tape in absolute format.

Each PDP-9 core configuration (8, 16, 24 and 32K) requires a separate set of paper tape

system programs. The ten system tapes supplied are:
FORTRAN IV
MACRO-9
PIP-9
Text Editor
Linking Loader
DDT (without Patch File capabilities)
DDT (with Patch File capabilities)

7 to 9 CONVERTER (CONV)
CHAIN
EXECUTE

4-3

In addition, the utility program PUNCH 9, which provides the ability to dump an executable
core load and .ABS loader onto paper tape, is provided with all paper tape systems. See Figure 4-1 for
memory maps of I/O Monitor System.
At the beginning of each tape is a Bootstrap Loader in hardware READIN mode. By setting
the starting address of the Loader* on the console address switches, depressing I/O RESET, and then
depressing the READIN switch, these system tapes may be loaded.
Since the tapes also contain appropriate versions of the I/o Monitor and the necessary I/o
device handlers, the system programs (FORTRAN IV, MACRO-9, Text Editor, CONV, PIP, CHAIN,
and EXECUT) can be loaded, ready for operation, in a single step.
Once the system program (FORTRAN IV, MACRO-9, Text Editor, CONV, PIP, CHAIN,
EXECUT or Linking Loader/DDT) has been loaded and takes control, the individual system program
operating procedures come into use. (See I/o Monitor Guide, oEC-9A-MIPA-D .)
User programs, however, normally exist in relocatable form, as output from FORTRAN IV or
MACRO-9; these tapes do not contain copies of the I/o Monitor. To load these programs, a copy of
the Linking Loader or DDT should be loaded first. The user should then initiate loading of his main
program followed by all required subprograms. By loading subprograms in order of size (largest first,
smallest last), the user has a better chance of satisfying core requirements for his program in systems
with extended core memory. The version of the I/O Monitor (including the device handlers) contained
on the Linking Loader or DDT tape may be used with user programs, and the Linking Loader or DDT can
be used to load the necessary device handlers as well as the user's object programs.

*17720 for 8192 word systems, 37720 for 16,384 words, 57720 for 24,576 words, and m20 for
32,768 words.

4-4

MEMORY MAP A
8K or 16K or
24K or 32K

SYSTEM PROGRAMS:

BOOTSTRAP
LOADER IN
HRM FORMAT

MEMORY MAP B-LINKING LOADER, CHAIN

FORTRAN
MACRO-9
EDITOR
PIP-9
7-9 CONVERTER

BK or 16K or

24K or 32K

• SCOM

BOOTSTRAP
LOADER IN
HRM FORMAT

• SCOM AND. SCOM + 3

USER
PROGRAMS

SYSTEM
PROGRAM

• SCOM +3

•

SYSTEM
PROGRAM
TABLE
SPACE

GLOBAL
SYMBOL
TAjLE

• seOM +2

LINKING LOADER
OR CHAIN
SYSTEM PROGRAM
DEVICE HANDLER

• SCOM + 2

PAPER TAPE
READER HANDLER

SYSTEM PROGRAM
DEVIC E HANDLER
•

SCOM + I

• SCOM +1

1/0 MONITOR
WITH TELETYPE -IN
AND
TELETYPE-OUT
DEVICE HANDLERS

1/0 MONITOR
WITH TELETYPE-IN
AND
TELETYPE-OUT
DEVICE HANDLERS

Refer to Section 7.4 for sizes for device handlers.

Figure 4-1

NOTE:
IN THE CASE OF CHAIN THE
PAPER TAPE PUNCH HANDLER
IS ALSO RESIDENT IN CORE.

Refer to Memory Map D for resu Its of Link ing Loader.

I/o Monitor System Memory Maps

4-5

MEMORY MAP C-DDT TAPE

MEMORY MAP D-USER PROGRAM READY
TO BE EXECUTED

8K or 16K or

24K or 32K

8K or 16K or

24K or 32K

BOOTSTRAP
LOADER IN
HRM FORMAT

BOOTSTRAP
• SCOM
•

SCOM

DOT
USER
PROGRAMIS)

• SCOM+3
USER DEVICE
HANDLER

U;ER
PROGRAMS

•

USER DEVICE
HANDLER
USER DEVICE
HANDLER

•

• SCOM +3

GLOBAL AND
DDT
SYMBOL ITABLES
• SCOM+Z

LINKING
LOADER

-------

lb.)

LINKING LOADER
DEVICE HANDLER

PAPER TAPE
PUNCH HANDLER

------LINKING LOADER
DEVICE HANDLER

PAPER TAPE
READER HANDLER
• SCOM +1

10.)

I/O MONITOR
WITH TELETYPE-IN
AND
TELETYPE-OUT
DEVICE HANDLERS

I/O
MONITOR
(INCLUDING
TELETYPE
HANDLER)

Refer to Memory Map E for results of Link Loading
in DDT mode.

Refer to Section 7.4 for sizes of device handlers.

Paper Tape Punch Handler is only present in DDT
versions with patch file capabilities.

. SCOM+l and. SCOM+2 both point to one of
two places and non-BLOCK DATA COMMON
(FORTRAN IV or MACRO-9) output may make
use of core as low as they point.
a.

If the user program did not have any device
handlers in common with the Linking Loader.

If the user program did have at least one device handler in common with the Linking
Loader.

Figure 4-1

I/o Monitor System Memory Maps (Cont)
4-6

MEMORY MAP F (EXECUTE)

MEMORY MAP E
8K or 16K or

8K or 16K or
24K or 32K

24K or 32K
BOOTSTRAP

4810

DDT

EXECUTE

352 10

USER
PROGRAM (SI

USER
PROGRAM(S)

USER/DDT
DEVICE HANDLER

LI BRARY
PROGRAM(S)

BOOTSTRAP

50 10

•

• SCOM

SCOM

USER/DDT
DEVICE HANDLER

USER DEVICE
HANDLER(S)
• SCOM + 3

NAMED COMMON
• SCOM+ 3
DDT CREATED
SYMBOLS AND
PATCH SPACE
•

SCOM +2

•

SCOM + I

DDT
SYMBOL
TABLE

IIIIIIIIIIIIIIII
LINKING LOADER
DEVICE HANDLER

LINKING LOADER
DEVICE HANDLER

I/O MON IT OR
(INCLUDING
TELETYPE
HANDLER I

BLANK COMMON
•

LINKING LOADER
BLOCK TRANSFER
ROUTINE

SCOM+ 2

EXECUTE'S
DEVICE
HANDLER

I/O MONITOR
( INCLUDING
TELETYPE
HANDLE R )

775 10

880 10

Refer to Section 7.4 for sizes for device handlers.
Non BLOCK DATA COMMON (FORTRAN IV
of MACRO-9 output) may make use of core as
low as the DDT symbol table. However, trouble
will occur if the user requests DDT to create
symbols or make patches that cause overlaying of the COMMON area.
The Linking Loader device handlers would have
been used to satisfy user device requests.

When the user types in the name of the XCT File
to be run, • EXECUTE brings in the first chain
from paper tape.
FORTRAN programs pass on data in blank common
starting at • SCOM + 2. Macro programs pass on
data between .SCOM + 2 and .SCOM + 3.
A call from the running chain to bring in another
chain is effected by transferring control back to
Execute.

Figure 4-1 I/O Monitor System Memory Maps (Cont)

4-7

4.3.2

Device Assignments
The device assignment table used by the I/O Monitor is fixed in length and in the assign-

ments it contains. It is composed of two sections; the upper section is for use by all system programs
except PIP, the lower section is referenced by all user programs and PIP,
The upper portion of the . OAT contains 13 slots, referenced as -1 through -15S ' The lower
section has S slots numbered 1 through lOS' The standard assignments for the device assignment table
for user programs and system programs other than PIP are shown in Figure 4-2, Figure 4-3 illustrates
PIP assignments, which include the Card Reader (CR01E, CR02B) and Line Printer as standard devices,
.DAT Slot
.DATBG

.DAT

Device

Handler*

-15

Paper Tape Punch

(PPA.)

Editor and Converter Output

-14

Paper Tape Reader

(PRA.)

Editor and Converter Input

-13

Paper Tape Punch

(PPB. )

MACRO-9, FORTRAN IV Output

-12

TTY Printer

(TTA.)

MACRO-9, FORTRAN IV and
Converter Listing

-11

Paper Tape Reader

(PRB.)

MACRO-9 FORTRAN IV Input

-10

Paper Tape Reader

(PRA.)

DDT -9 Input and Editor,
MACRO-9 Secondary Input

-7

-6

Paper Tape Punch

-5

-4

Paper Tape Reader

(PRA.)

System Input (Linking Loader)

-3

TTY Printer

(TTA.)

Teleprinter Output

-2

TTY Keyboard

(TTA.)

Keyboard Input

-1

Paper Tape Reader

(PRA. )

System Device (Linking Loader)

TTY Printer

(TTA.)

Teleprinter Output

TTY Keyboard

(TTA.)

Keyboard Input

Paper Tape Reader

(PRA.)

Input

TTY Printer

(TTA.)

Listing

Paper Tape Punch

(PPA.)

Output

Paper Tape Reader

(PRA.)

Scratch

Paper Tape Punch

(PPA.)

Scratch

Paper Tape Reader

(PRA.)

Scratch

Use

Not Used
(PPA.)

DDT -9 Output
Not Used

.DAT

.DATND =,

Figure 4-2 Device Assignment Table (.DAT) for I/o Monitor
*See Section 7.4 for a description of the handlers.

4-S

The negative • OAT slot assignments for use by system programs may be changed by DEC.
For example, • OAT slot -10 might be associated with a card reader, while .DAT slot -12 could be
assigned to a line printer. Provision for changing positive • OAT slot assignments for use by relocatable
user programs is included in the PUNCH9 utility program (see section 4.3.5). For example, a magnetic tape handler (MTF) or one of the drum handlers (ORA, ORB, DRC, ORO) could be added.

Handler

Use

Teletype

(TTA.)

Input/Output

Teletype

(TTA. )

Input/Output

Paper Tape Reader

(PRA. )

Input

Line Printer

(LPA. )

Output

Paper Tape Punch

(PPA. )

Output

Card Reader

(COB.)

Input

Paper Tape Punch

(PPA. )

Output

Paper Tape Reader

(PRA. )

Input

. OAT Slot

Device

Figure 4-3

4.3.3

Device Assignment Table (.DAT) for PIP

Error Detection and Handling

Comprehensive error checking is provided by the Linking Loader and the Input/Output Programming System. Detailed lists of errors that may occur are given in Appendix 0 and E, respectively.
The other system programs also provide comprehensive error checking. Refer to the appropriate PDP-9
ADVANCED Software System manual (listed at the beginning of this section) for detailed information
on these errors.

4-9

4.3.4

Control Character Commands in the I/o Monitor Environment
All control character commands recognized by the I/o Monitor are summarized in Table 4-1.

These commands (except RUBOUT) are formed by holding down the CTRL key while striking a letter key.
The character or characters echoed on the Teletype and the resulting action is given in the table for
each command.
Table 4-1
Control Character Commands
Action

Command

Echo

CTRL S

t S

Starts user program after Linking Loader has brought it into core
via a LOAD command.

CTRL T

t T

CTRL T is applicable only when using DDT and forces control
back to DDT which types
DDT

>
to indicate its readiness for another DDT command. All previous
DDT conditions remain intact (breakbpoints, register modifications,
etc.) .
CTRL R

t R

Allows the user to continue when an lOPS 4 (device not ready)
error occurs. The user must first ready the device, and then type
CTRL R.

CTRL P

t P

Forces control to last address specified in the .INIT command
referencing Teletype. Used by system programs to reinitialize
or restart.

CTRL U

Cancels current line on Teletype (input or output).

RUBOUT

Cancels last character input from Teletype (not applicable with
DDT).

4.3.5

Modifying System Programs and Building Executable User Core Loads in the I/o
Monitor Environment
The capability of modifying or patching system programs in the I/o Monitor environment is

provided by the utility program PUNCH9. PUNCH9 allows for producing an executable core load on
paper tape in .ABS format with the standard .ABS loader (HRM 17720 of the highest available core
bank) on the front of the tape. This is particularly useful when the core load consists of a relocatable
main program, subroutines and library routines, the repetitive loading of which tends to be time consuming. It is further possible to specify the number of .ABS tapes to be output (1-9) for convenience
of tape hand ling.

4-10

The areas of memory output by PUNCH9 are 0 up to .SCOM + 2 (the first free cell) and
.SCOM + 3 (last free cell) up to the .ABS loader (17720 module SK). PUNCH9 is loaded (I/O RESET
and REAOIN) at 17720 of the highest core bank available. It loads and relocates part II of itself in
free core, i.e., from the cell in • SCaM + 2 and up. When loaded it types the following message on
Teletype:
P,TorS?J

>
The user is expected to type t P or tT or t S to define the starting location of the program to be punched
followed by carriage return (1 tape) or a number (1-9) specifying the total number of tapes into which
binary output is to be divided.

tT should be used if DDT is part of the core load.
tp should be used for all other system programs and user programs which have already
initialized (.INIT) the Teletype with a RESTART address at the time PUNCH9 was executed.
t S should be used only if the core load was output by PUNCH9 after Linking Loader operation

at the moment when the loader itself was expecting the ts command. All tapes output by PUNCH9 are
loaded by hitting I/O RESET and the REAOIN key with ADDRESS switches set to 17720 of the highest
core bank.

4.3.5.1

Modifying User. OAT Slots in the I/O Monitor Environment - Although it is not possible to

reassign negative • OAT slots at load time in the I/O Monitor environment for system programs (reassembly
is required), PUNCH9 provides this capability for the user or positive. OAT slots.
For example, Figure 4-2 lists the standard .OAT slot assignments. A relocatable user program
wanting to use drum (handlers ORA., ORB., ORC. or ORO.) or magnetic tape (MTF.) or card reader
(COB.) or line printer (LPA.) whose handlers are included in the paper tape library has no way of doing
so unless he can modify the positive. OAT table. The modifications procedure is as follows:

Load the Linking Loader (or DDT) tape into core (HRM 17720 modulo SK).

2. Stop the computer and modify the appropriate . OAT slot cell (.OAT = 135) according
to the Loader - I/O correspondence table below. For example, if • OAT slot 7 is to be assigned to
drum unit 1 using handler ORO., cell 144 should be changed to 100013. *
3.

Load PUNCH9 into core (HRM 17720 modulo SK).

Type tp in response to the query from PUNCH: lip, Tor S?"

Load the resultant punched tape into core (HRM 17720 modulo SK).

*Note: The unit number is stored in bits 0-2.

4-11

The Loader will restart, ready for acceptance of typed program names to be loaded.

If . OAT slot 7 is referenced by the user program (e.g., IOOEV 7), ORO. for drum unit 1 will be loaded
from the I/O Library.

Loader - I/O Correspondence
Handler

.OAT Slot Value

TTA.
PRA.
PRB.
PPA.
PPB.
PPC.

3
4
5
6
7

LPA.

COB.
MTF.

11
13**
14**
15**
16**
17**

ORA.
DRB.
DRC.

ORO.

** With unit number in bits 0-2.

4-12

CHAPTER 5
KEYBOARD MONITOR

5.1

KEYBOARD MONITOR FUNCTIONS
The Keyboard Monitor is designed to operate with a PDP-9 that has some form of bulk storage

(see Hardware Requirements, Section 1.2). It includes all elements of the Input/Output Monitor in addition to routines that accept and interpret Teletype keyboard commands, change device assignments,
and automatically load and initiate system and user programs.
The reader is referred to Chapter 2 for a general discussion of the monitor environment, and
to Chapter 3 for a detailed description of user program commands (system macros) available in the Keyboard Monitor environment. The Keyboard Monitor Guide (DEC-9A-MKFA-D) contains detai led operating procedures for system programs mentioned in this chapter and a good example (Appendix J) of
an actual keyboard session using system software.

5.2

PROGRAMMING EXAMPLE
The following example illustrates the use of system macros with MACRO-9 programs in the

Keyboard Monitor Environment. The example inputs a Iine of data from the Teletype keyboard, writes
it on DECtape, reads it back from DECtape, and outputs it on the Teletype. Before subsequent keyboard inputs, the program pri nts the messages:
FILE ALREADY PRESENT! !
DO YOU WISH TO KEEP IT? (Y OR N) AND CR.
By typing Yon the keyboard, the file is saved and a new file is created for the next line of input from
the keyboard.

By typing N on the keyboard, the next line of data input from the keyboard is written

on DECtape with the same fi Ie name given to the previous line.
The name of the file is initially ECHO TST. The file name for each new file (providing that
the previous file was not deleted) is obtained by incrementing location NAME+l. This produces a series
of files, ECHO TST, ECHO A TST, ECHO B TST, ECHO C TST, ••• etc., (since the alphabet in .SIXBIT
begins 01 8 , 02 8 , 03 8 , etc).
The arguments used by the system macros are given symbolic names by means of MACRO-9
direct assignment statements at the beginning of the program to faci litate recall for the programmer,
and to change the arguments readily. The partial assembly listing that follows the example shows how
the first several system macros are expanded at assembly time.
expansions with the system macro descriptions in Chapter 3.)

5-1

(The reader may wish to compare these

Example:

DECTAPE=7
TT!=S
TTO=5
IN=0
OUT=l
IOPS=2
START

READKB

II/RITE

REA DDT

RESTRT

UPDATE

.TITLE DTECHO

• IODEI)
• I NIT
• I NIT
• I NIT
.l<'STAT
SZA
JMP
.READ
• ',A/AIT
LAC
SZA
JMP
.ENTER
• II/RITE
.'A/AIT
.CLOSE
• PH T

.SEEK
.READ
• 'I/A IT
.'A/RITE
.'A/ .UT
.CLOSE
.CLOSE
.CLOSE
JMP
.'A/RITE
.'4~IT

• 'I/RITE
.'4AIT
.READ
• "JAIT
LAC
A"JD
SAD
JMP
DZM
JMP
YES
NEWJ<I L
MSGI

MSG2

5,6,7
DECTAPE,OUT,RESTRT
TTI,IN,Rl:!...;,TRT
TTO,OUT,RESKT
DECTAP,NAME

IINITIALIZE DECTAPE OUTPUT,
ITELETY. E I ~PUT ,
lAND TELETYE OUTPUT
lIS FILE PRESENT?
INO, I~PUT KEYBOARD
UPDATE
IYES, OUTPUT MSGI AND MSG2
TT1,IOPS,BUFFER,34 IINPUT lOPS ASCII FROM KEYBOARD
TII
IWAIT UNTIL I~PUT COMPLETE
UDSI4
ITEST UPDATE SWITCH
I~ R~. L~CE INPUT FILE
NEWFIL
I-I=SAVE INPUTI CREATE NEW OUTPT
DECTAP,NAME
ILOCATE FREE DECTAPE FILE
DECTAP,IOPS,BUFFER,34
10UTPUT DATA ON DECTAP
DECTAP
I~AIT UNTIL OUTPUT COMPLETED
DECTAP
ICLOSE FILE
DECTAP,IN,RESTRT
II~IrIALIZE DECTAPE INPUT
DECTAP,~~ME
ILOCATE FILE "NAME"
DECTAP,IOPS,9UFFER,34
IREAD INTO SUFFER
DECTAP
IWAIT UNTIL READ COMPLETE
TTO,IOPS,9UFFER,34 IOUTPUT TO TELETYPE
TTO
IWAIT UNTIL OUTPUT COMP~ETE
TTO
ITERMINATE TELEfYPE OUTPUT,
TTl
ITELETyPE INPUT,
DECTAP
lAND DECTAPE INPUT/OUTPUT
START
ILOOP FOR UPDATE OPTION
TTO,IOPS,MSSl,34
10UTPUT MSGI
TTO
lAND MS32
TTO,IOPS,MSG2,34
10~
TTO
ITELETYPE
TTI,IOPS,COM,g
IREAD RESPONSE
TTl
IWAIT UNrI~ READ COMPLETE
COM+2
IGET FIRST WORD
(774000
ISAVE FIRST SEVEN BITS
~544000
lIS CHA~ A Y?
YES
IYES
UDSW
INO, SET TO REPLACE INPUT FIL~
READKB
ILOOP TO READ KEYBOARD

CLC
DAC
UDSla/
JMP
READKB
ISZ
NAME+I
JMP
'~RI TE
MSG2-MSGl/2*1000

ISET UPDATE S~. TO SAVE
IINPUT, CREATE NE~ OUTPUT
ILOOP TO READ KEYBOARD
ICHAN3E FILE NAME
ITO CREATE NEW OUTPUT
IWPC FOR HEADER WORD 0

.ASCII "FILE ALREADY"
.ASCII "PRESENT!!"cI5>
COM-MSG2/2*1000

IWPC FOR HEADER WORD 0

o
o

5-2

COM
BUFFER
NAME
UDSIaI

.ASCII "DO yOU WISH TO KEEP IT?"
.I\SCII "CY OR N) AND CR."<15>
IRESPONSE BUFFER
10
.BLOCK
IDATA BUFFER C34 DECIMAL>
42
.BLOCK
IF! LE NAME
• SIXBIT "ECHO@@TST"
IUPDATE SWITCH
o
START
.END

ASSEMBLY LISTING:
DTECHO

PAGE
• TITLE
000007
000006
000005
000000
000001
000002

A
A
A
A
A
A

00000
00000
00001
00002
00003

R
R
R
R
R

001007
000001
000070
000000

A GEN*
A GEN*
R GEN*
A GEN*

00004
00005
00006
00007

R
R
R
R

000006
000001
000070
000000

A GEN*
A GEN*
R GEN*
A GEN*

00010
00011
00012
00013

R
R
R
R

001005
000001
000070
000000

A GEN*
A GEN*
R GEN*
A GEN*

00014
00015
00016
00017
00020
00021
00021
00022
00023

R
R
R
R
R
R
R
R
R

003007
000002
000246
740200
600077

A GEN*
A GEN*
R GEN*
A
R

002006
000010
000204

00024

777736

A GEN*
A GEN*
R GEN*
GEN*
A GEN*

00025
00026
00027
00030
00031
00032
00032
00033
1710034

R
R
R
R
R
R
R
R

000006
000012
200251
740200
600132

A GEN*
A GEN*
R
A
R

000007
000004

A GEN*

DTECHO

DECTAP=7
TTI=6
TTO=5
IN=0
OUT=1
lOP S =2
5,6,7
.IODEV
DECTAP,OUT,RESTRT
• INIT
CAL+OUT*1000 DECTAP&777
1
RESTRT
0
TTI,IN,RESTRT
• INIT
CAL+IN*1000 TTI&777
1
RESTRT
0
.INIT
TTO,OUT,RESTRT
CAL+OUT*1000 TTO&777
1
RESTRT
0
.FSTAT
DECTAP,NAME
CAL+3000 DECTAP&777
2
NAME
SZA
JMP
UPDATE
.READ
TTI,IOPS,BUFFER,34
CAL+IOPS*1000 TTI&777
10
BUFFER
.DEC
-34
.WAIT
TTl
CAL TTI&777
12
LAC
UDSW
SZA
JMP
NEWFIL
DECTAP,NAME
.ENTER
CAL DECTAP&777

START

READKB

WRITE

5-3

5.3

KEYBOARD COMMANDS
The Keyboard Monitor provides three advantages over the Input/Output Monitor:
a.

The ability to request system information and directions for system operation.

b. I/O device independence, through the ability to dynamically change I/o device assignments before loading a program.
c.

The ability to call, load, and execute system and user programs via simple keyboard

commands.
When the Keyboard Monitor initially gets control it outputs
MONITOR

$
to the teleprinter to indicate readiness to accept a keyboard command. Subsequently, it outputs only
the dollar sign ($) to indicate readiness. In both cases, the keyboard command should be typed on the
same line as the dollar sign ($).
Keyboard Monitor commands fall into three categories:
a.
ALT MODE).
b.

Commands that load system programs (terminated with a carriage return (J) or
Commands to perform special functions.

c. Control character commands, formed by holding down the CTRL key while striking a
letter key. These commands are used during the running of system or user programs. (System programs
echo contro I character commands by typing an up arrow (t) fo IIowed by the assoc iated character.)

5.3. 1

System Program Load Commands
Loading commands instruct the Keyboard Monitor to bring in the System Loader which is used

to load all system programs from the system device. The commands which follow are available to the
user for loading systems programs via the Keyboard Monitor.

System Program Loaded

Command

FORTRAN IV Compi ler

F4A

Abbreviated FORTRAN IV Compiler

MACRO

MACRO-9 Assembler

MACROA

Abbreviated MACRO-9 Assembler

PIP

Peripheral Interchange Program

EDIT

Symbolic Text Editor

CONV

7 -to-9 Converter

LOAD

Li nk i ng Loader

GLOAD

Linking Loader (set to load and go)

5-4

System Program Loaded

Command
DDT

Dynamic Debugging Technique program

DDTNS

DDT program with no user symbol table

UPDATE

Library Fi Ie Update program

DUMP

Program to dump saved area (see CTRL Q and QDUMP commands)

PATCH

System tape Patch program

CHAIN

Modified version of Linking Loader (allows for chaining)

EXECUTE{E)

Control program to load and execute chained programs

SGEN

System Generation program

All commands should be terminated by a carriage return (CR) or ALT MODE (ESC). When
the requested program has been loaded and is waiting for keyboard input ,an indication is given on the
Teletype with an appropriate message; such as
LOADER

>
or

FORTRAN 4

>
or

EDITOR

>
etc.

5.3.2

Special Function Commands
The special-function keyboard commands available in the Keyboard Monitor environment

are described in the following paragraphs.

5.3.2.1

LOG (or L) - The LOG command is used to make hard copy records of user comments on the

Teletype. When the LOG command is encountered, the Monitor ignores all typing up to and including
the next ALT MODE.
Example:
$LOG THIS IS AN EXAMPLE. (ALT MODE)

5.3.2.2

SCOM (or S) - The SCOM command causes typeout of system configuration information, in-

cluding available device handlers, the skip chain order, and manual restart and dump procedures.

5-5

Example:
$SCOM
SYSTEM INFORMATION -

V4B

9/30/68

17646 - BOOTSTRAP RESTART ADDRESS
17636 - 1ST FREE LOCATION BELOW BOOTSTRAP
1635 - 1ST FREE LOCATION ABOVE RESIDENT MONITOR
135 - ADDRESS OF .DAT
536 - tQ ADDRESS FOR MANUAL DUMP
101 - START BLOCK FOR tQ DUMP AREA
2~0 - KM9 START WITH RESTART ADDRESS IN LOCATION 0
DEVICE HANDLERS AVAILABLE:
TTA TELETYPE: INPUT/OUTPUTI ASCII MODESI ALL FUNCTIONS
PRA PAPER TAPE READER: INPUTI ALL MODESI ALL FUNCTIONS
PRB PAPER TAPE READER: INPUTI lOPS ASCII MODEl ALL FUNCTIONS
PPA PAPER TAPE PUNCH: OUTPUT I ALL MODES I ALL FUNCTIONS
PPB PAPER TAPE PUNCH: OUTPUTI ALL MODES LESS lOPS ASCIII ALL FUNCTIONS
PPC PAPER TAPE PUNCH: OUTPUTI lOPS BINARY MODEl ALL FUNCTIONS
DTA DECTAPE: 3 FILESI INPUT/OUTPUTI ALL MODES I ALL FUNCTIONS
DTB DECTAPE: 2 FILESI INPUT/OUTPUTI lOPS MODESI LIMITED FUNCTIONS
DTC DECTAPE:
FILEI INPUTI lOPS MODESI LIMITED FUNCTIONS
DTD DECTAPE: 1 FILEI INPUT/OUTPUTI ALL MODESI ALL FUNCTIONS
LPA LINE PRINTER: OUTPUTI lOPS ASCII MODEl ALL FUNCTIONS
CDB CARD READER: INPUTI lOPS ASCII MODEl ALL FUNCTIONS
SKIP CHAIN ORDER
SPFAL
DTDF
RCSF
CLSF
LSDF
RCSD
RSF
PSF
KSF
TSF
DTEF
SPE
MPSNE
MPSK

5.3.2.3

API ON/OFF - This command controls the status of the Automatic Priority Interrupt if avail-

able in the system. API ON enables the API; API OFF disables the API.
Example:
$APIOFF

5.3.2.4

QDUMP (or tQ)* - In the event of an unrecoverable error, this command conditions the

monitor to dump memory on the "save area" of the system tape (or other unit at the system device if
used).
*The QDUMP and HALT commands are mutually exclusive and have no effect if a DDT load.

5-6

QDUMP forces automatic execution of the CTRL Q command (described later) on all non-recoverable
error calls to the Monitor Error Diagnostic (.MED) program. It must be issued prior to the LOAD,
GLOAD, DDT, or DDTNS command used to load the user program.

(QDUMP issued prior to a GET,

has no effect after the GET since the Monitor at CTRL Q time overlays the monitor primed by QDUMP.)
Note that the WRITE switch on the system device should be enabled in case of error; otherwise, an
lOPS 4 (not ready) error will follow the initial error.

5.3.2.5

HALT (or H)* - This command conditions the Monitor to print an error message and halt in

the event of an unrecoverable lOPS error.

Depressing the CONTINUE button reloads the Monitor.

HALT must be issued prior to the LOAD, GLOAD, DDT, or DDTNS command. (HALT is issued prior
to a GET, has no effect after the GET since the Monitor at CTRL Q time overlays the Monitor primed
by the HALT command.)

5.3.26

INSTRUCT (or I) - The INSTRUCT command can be used in two ways: INSTRUCT alone

causes a summary of Monitor commands to be printed on the Teletype; INSTRUCT ERRORS causes a
summary of system error messages to be pri nted.
Example:

$INSTRUCT
MONITOR: INFORMATION AND MODIFICATION COMMANDS
LOG(L): USER COMMENTS TERMINATED BY ALTMODE
SCOM(S): SYSTEMS INFORMATION
INSTRUCT(I): LIST OF MONITOR COMMANDS
INSTRUCT(I) ERRORS: DESCRIPTION OF ERROR CODES
REQUEST(R), REQUEST(R) PRGNAM: .DAT SLOT USAGE
REQUEST(R) USER: POSITIVE .DAT SLOT USAGE
ASSIGN(A) DEVN A,B, ••• /ETC.: .DAT SLOT MODIFICATIONS
DIRECT(D), DIRECT(D) M: DIRECTORY OF UNIT 0 OR M OF SYSTEM DEVICE
NEWDIR(N) M: CLEAR DIRECTORY OF UNIT M OF SYSTEM DEVICE
QDUMP(Q): SET TO SAVE CORE (tQ) ON .IOPS ERROR
HALT(H): SET TO HALT ON .IOPS ERROR
rQN: SAVE CORE ON UNIT N
GET(G) N: RESTORE CORE FROM UNIT N AND RESTART
GET(G) N X: RESTORE CORE FROM UNIT N AND START AT X
GET(G) N HALT(H):RESTORE CORE FROM UNIT N AND HALT
API ON/OFF: CHANGE STATE OF API
tC: RESTORE MONITOR
tP: USER RESTART

*The QDUMP and HALT commands are mutually exclusive and have no effect if a DDT load.

5-7

MONITOR: PROGRAM LOADING COMMANDS AND PRGNAM FOR REQUEST COMMAND
LOAD: LINK LOADER AND STOP
GLOAD: LINK LOADER AND GO
DOT: LINK LOADER WITH SYMBOLS AND GO TO DOT
DDTNS: LINK LOADER WITHOUT SYMBOLS AND GO TO DOT
MACRO: SYMBOLIC MACRO ASSEMBLER
MACROA: ABBREVIATED SYMBOLIC MACRO ASSEMBLER
F4: FORTRAN IV COMPILER
F4A: ABBREVIATED FORTRAN IV COMPILER
EDIT: SYMBOLIC CONTEXT EDITOR
PIP: PERIPHERAL INTERCHANGE PROGRAM
SGEN: SYSTEM GENERATOR
DUMP: BULK STORAGE DEVICE DUMP
UPDATE: LIBRARY FILE UPDATE
CONV: 7-TO-9 CONVERTER
PATCH: SYSTEM TAPE PATCH ROUTINE
EXECUTE(E) FILE: LOAD AND RUN FILE XCT
CHAIN: XCT CHAIN BUILDER
MONITOR: BATCH PROCESSOR
BATCH(B) DV: ENTER BATCH MODE WITH DV AS BATCH DEVICE
DV: PR = PAPER TAPE READER
CO = CARD READER
$JOB: CONTROL COMMAND WHICH SEPARATES JOBS
$DATA: BEGINNING OF DATA - NOT ECHOED ON TELETYPE
$END: END OF DATA
$EXIT: LEAVE BATCH MODE
TT: SKIP TO NEXT JOB
TC: LEAVE BATCH MODE

5.3.2.7

REQUEST (or R) - The REQUEST command allows examination of the. OAT slots associated

with various programs.* The command takes the following form:

xxxxxx

REQUEST

where XXXXXX is the system program name (that is I the system program load command), or USER for
all positive • OAT slots, or blank for an entire • OAT table printout.
Examples:
$REQUEST
.DAT

DEVICE

USE

-15
-14
-13
-12
- 11
-10
-7

DTA2
DTAI
PPC0
TTA0
DTCI
TTA0
DTC0
NONE

OUTPUT
INPUT
OUTPUT
LISTING
INPUT
INPUT
SYSTEM DEVICE FOR .SYSLD
OUTPUT

-6

*See Section 7.3 for. OAT slots used by system programs, their uses, and acceptable I/o handlers.

5-8

-5
-4

-3
-2
-1
1
2
3
4
5
6
7

11Z1

NONE
PRAIZI
TTAIZI
TTAIZI
DTCIZI
DTAIZI
DTA1
DTA2
TTAIZI
PRAIZI
PPAIZI
DTA1
DTA2

EXTERNAL LIBRARY FOR .LOAD
SYSTEM INPUT
TELEPRINTER OUTPUT
KEYBOARD INPUT
SYSTEM DEVICE FOR .LOAD
USER
USER
USER
USER
USER
USER
USER
USER

$REQUEST MACRO
.DAT

DEVICE

USE

-13
-12
- 11
-11Z1
-3
-2

PPCIZI
TTAIZI
DTC1
TTAIZI
TTAIZI
TTAIZI

OUTPUT
LISTING
INPUT
SECONDARY INPUT
CONTROL AND ERROR MESSAGES
COMMAND STRING

5.3.2.8

ASSIGN (or A) - The ASSIGN command allows reassignment of • OAT slots to devices other

than those set at system generation time. The change of assignment is only effective for the current
job, since the permanent assignments are restored when control is returned to the Monitor. The command takes the following form:
ASSIGN DEVn a, b, etc/DEVm x, y, etc.
where DEV is the device handler name (the list of legal handlers for a particular system may be requested
via the SCOM command*). If the third letter of a handler name is omitted, the letter A is assumed.
n, m are unit numbers (if none specified, 0 is assumed)
a, b, x, y, etc., are • OAT slot numbers
Examples:
$ASSIGN DTAO -10, -6/PRA -5
(An equivalent command would be $ASSIGN DT -10, -6/PR -5)
$ASSIG N PPB

-6/DTB2 3/DTB3 5

$ASSIGN DTAl

6, 7, 10

*See Section 7.3 for. OAT slots used by system programs, their uses, and acceptable I/O handlers.
Many of the devices, DECtape for example, have more than one I/O handler associated with them. It
is imperative that only one version of a device handler be present during a particular run since confusion occurs because of the lack of communication between the two interrupt handlers.

5-9

DEVn can be replaced by NONE or NON to clear. DAT slots.
$ASSIGN NONE 4, 5, 10
. DAT slots -2 and -3 are permanent and should not be modified .
. DAT slot -7 should be modified only at system generation time.

5.3.2.9

DIRECT (or D) - The DIRECT command allows printout of the directory associated with any

unit on the system device control (that is, eight units, 0 through 7, on DECtape control).
The command takes the following form:
DIRECT N
where N is the unit number (unit 0 is the default assumption).
Example:

$DIRECT
DIRECTORY LISTING
.LIBR BIN
1 LJ 1
DDT9
BIN
1 LJ2
.LOAD BIN
1 LJ3
CHAIN BIN
ILJLJ
INTEGE EAE
ILJ5
INTEGE NON
152
REAL
EAE
16LJ
REAL
NON
215
KM9
SYS
0
.SGEN2 SYS
36
SKPBLK SYS
LJLJ
UPDATE SYS
LJ5
.SYSLD SYS
56
EXECUT SYS
67
rQAREA SYS
101
PATCH SYS
652
EDIT
SYS
657
PIP
SYS
671
FLJ
711
SYS
MACRO SYS
7 LJ2
FLJA
SYS
771
MACROA SYS 1020
DUMP
10LJLJ
SYS
·SGENI SYS 1050
CONV
SYS
106LJ
70
FREE BLOC KS

5.3.2.10

NEWDIR (or N) n - This command refreshes the directory on the specified unit (n) of the

system device control (unit 0 illegal).

5-10

5.3.2.11 GET (or G) - This command has three forms as follows: GET n, GET n xxxxx, or GET n HALT.
The letter n is the number (0 through 7) of a unit on system device control that contains the tQ area to
be retrieved, and xxxxx is a program starting address.
GET retrieves the core image (including the Monitor) stored on unit n on the system device
control by CTRL Q commands, and restores it to memory. Control is transferred to xxxxx, if specified;
execution halts if HALT was specified. To start in this case, the extended memory switch should be
raised if the machine is greater than 8K, and the starting address should be placed in the ADDRESS
switches and the START button depressed (PIC and API are enabled). If neither xxxxx not HALT are
specified, the job is restored in memory and the resident Monitor waits in a Teletype loop with API
and/or PIon for one of the following commands to be typed:
tP

(restart any system program and user programs whi ch have issued an
. I N IT to the Tel etype wi th a restart address.

(restarts DDT)

(starts a relocatable user program - used only if tQ had been executed
at the completion of a link load when the loader was waiting for tQ to
by typed.)

5.3.2.12 CHANNEL (or C) 7/9 - This command causes the default operation bit (.SCOM + 4, bit 6)
to be cleared or set. If this bit is 0, then 7 channel operation is assumed by the MAGtape handler. If
it is 1, the 9 channel is assumed. This default condition can also be set at system generation time by
answering yes or no to the question
"SHOULD DEFAULT ASSUMPTION BE 7 CHANNEL MAGTAPE?"
5.3.2.13 339 (or 3) ON/OFF - This command tells the monitor that a 339 handler is to be loaded.
A 30 8 register block is reserved for the push-down list. If a 339 display handler is loaded and the
push-down list has not been reserved, an .IOPS 24 error will occur on the first .INIT to that handler.
The default condition of the 339 ON/OFF bit (.SCOM+4, Bit 5) can be set at system generation time
by answering YES to the question,
"SHOULD DEFAULT ASSUMPTION BE A 339 LOAD?"
5.3.2.14 VC38 (or V) ON/OFF - This command causes the character display table for the VC38 option
to be set up prior to loading of any system or user programs. If this table is not set up and the user does
not specify a character table in the first. INIT to the handler, the display handler wi II assume the presence of a VC38 for text manipulation. The default condition of the VC38 ON/OFF bit (.SCOM+4,
bit 4) can be set at system generation time by answering YES to the question,
"SHOULD VC 38 CHARACTER TABLE BE LOADED?"

5-11

NOTE
If 339 is ON (bit 5 of • SCOM+4=l), then the address of
the push-down I ist is initially set to zero. However, if
VC38 is ON (bit 4 of . SCOM+4=l) , then the first register of the push-down list points to the starting address of
the VC 38 table.

5.3.3

Control Character Commands
All control character commands recognized by the Monitor are summarized in Table 5-1.

Table 5-1
Control Character Commands
Action

Command

Echo

CTRL S

Starts user program after Linking Loader has brought it into core
via a LOAD command.

CTRL C

Forces control back to Monitor which types
MONITOR

$
to indicate that it is awaiting a keyboard command. If the nonresident section of the Monitor was in core, the Monitor is not
reinitialized; thus, previous conditions, such as .DAT slot assignments, remain as they were prior to CTRL C. If the nonresident section of the Monitor was not in core, it is brought in
and all conditions revert to the standard.
CTRL T

CTRL T is applicable only when using DDT or when operating in
the BATCH mode. If DDT is being used, CTRL T forces control
back to DDT which types
DDT

>
to indicate its readiness for another DDT command. All previous
DDT conditions remain intact (for example, breakpoints, register
modifications, etc.). When operating in BATCH mode, CTRL T
causes a skip to the next job.
CTRL R

Allows the user to continue when an lOPS 4 (device not ready)
error occurs. The user must first ready the device, and then
type CTRL R.

5-12

Table 5-1 (Cont)
Control Character Commands
CTRL P

Forces control to address specified in the last .INIT command referencing Teletype. Used by system programs to reinitialize or restart.

CTRL Q n

Dumps the current job, in core image, onto prespecified blocks
of unit n on the system device control {the WRITE switch on this
unit must be enabled}. For example, when the system device is
DECtape unit 0, CTRL Q requests can be made to DECtape only.
The core image may be retrieved and reloaded by the GET command or examined by using the DUMP command to load the system Dump program. CTRL Q is honored whenever typed.

CTRL U

Cancels current line on Teletype {input or output}.

RUBOUT

Cancels last character input from Teletype {not applicable with DDT}.

5.4

OPERATING THE KEYBOARD MONITOR SYSTEM
The reader is referred to the Keyboard Monitor Guide {DEC-9A-MKFA-D} for detailed

operating procedures for system programs in the Keyboard Monitor environment. The following PDP-9
ADVANCED Software System manuals contain additional detailed information on system programs.
Manual

Document Number

Uti I ity Programs

DEC-9A-GUAB-D

MACRO-9 Assembler

DEC-9A-AMZA-D

FORTRAN IV

DEC-9A-KFZA-D

This section contains descriptions of loading the Keyboard Monitor, system generation, assigning devices, loading programs, and error detection and handling.
5.4.1

Loading the Keyboard Monitor
Each installation employing the DECtape version of the Keyboard Monitor must reserve tape

unit 0 as the system device. This unit will contain the system tape, which includes the Monitor, the
Input/Output Programming System, and all system and library programs needed by the user.
A System Bootstrap is supplied on paper tape in hardware READIN format. By setting the
starting load address of the bootstrap (17637 of the highest memory bank available) on the console address switches, depressing I/O RESET and then the READIN switch, the bootstrap is loaded into upper
core. It clears the flags, turns on EXTEND MODE, disables the program interrupt {and the automatic
priority interrupt, if avai lable}, loads the Keyboard Monitor from the system device into lower core,
and transfers control to it. The Monitor types
MONITOR

$
when it is ready to accept commands from the user.

5-13

The System Bootstrap may be restarted without reloading the paper tape, if it has not been
destroyed, by setting the ADDRESS switches to 17646 of the highest memory bank, depressing I/O RESET
and then START.
Ease of operation in an 8K DECtape environment will be enhanced by noting the following
system characteristics, all of which are concerned with a judicious choice of I/o handlers (see Section
7.3 and 7.4) for system program operations:
a. .DAT slots -11 and -13 have been standardly assigned to handler DTB. to facilitate use
of MACROA and FORTRAN IV A with DECtape input and DECtape output. Consequently, a reassignment of .DAT slots -11 and/or -13 is required in order to use MACRO or FORTRAN 4. If this reassignment is not performed the user may expect a . SYSLD 1 (core overflow) error.
b. .DAT slot 6 has been assigned to PPB (the punch handler for all data modes except lOPS
ASCII) in order to facilitate loading PIP with the optimum combination of I/O handlers. Since paper
tape reproduction of any paper tape may be accomplished using the I data mode, the user is seldom inconvenienced. If, however, PPA. is sometimes desired, the other positive .DAT slots will have to be
examined for appropriate reassignment.

5.4.2

System Generation
PDP-9 installations with Disk but not DECtape receive PDP-9 ADVANCED software as a set

of paper tapes which can be used to create a system tape. Installations that have DECtape will receive
a system tape on 0 ECtape •
System Generator (.SGEN) is a standard system program (bulk storage systems only) used to
create new system tapes. Upon receiving a PDP-9 bulk-storage system, the user should immediately
create a standard system tape for his installation. This is done by loading the System Bootstrap, which
calls the system into core, and using the Keyboard Monitor to call the System Generator. . SGEN will
output the new system tape on the device associated with .DAT slot -15; the ASSIGN command should
be used prior to calling. SGEN to assign a bulk storage device to slot -15 and the old system device
to slots -10 and -14, that is,
$ASSIGN DTAO -14, -10/OTA2 -15 (or DKD2 -15*) J
$SGEN J
Once loaded, . SGEN communicates with the user in a conversational mode via the Teletype to obtain
information needed to create a system tape. Among the items of information it needs to know are:

*It is imperative that the Disk "0" handler be used when generating from DECtape to Disk to avoid
core overflow. Conversely, generating from Disk to DECtape requires:
$ASSIGN DKAO -14, -10/OTD2 -15 J

5-14

On which device the system tape will operate, so that

The system device slots in the device assignment table (. DAT) can be set.

The PIC skip chain and API channels can be set up for the system device.

b. All device skips present in the PIC skip chain and their order. Non-basic devices can
be added to the skip chain at this time, by supplying the device mnemonic and the skip IOT(s}.
c.

Total core capacity (8, 16, 24, or 32K) of the installation.

Special options present at the installation (API, EAE, etc.)

e.
be assigned.

The structure of • DAT. All system slots (-1 through -15) and slots 1 through 10 shou Id

When .SGEN has received all of the information necessary, it creates a new system tape,
then returns control to the Monitor. New system tapes can be created whenever a significant change
in the installation configuration occurs. A good example of a complete system generation session is
given in the Keyboard Monitor Guide (DEC-9A-MKFA-D).
The following paragraphs are intended to assist Keyboard Monitor users in their initial efforts
at "tailor making" a system for their installation. The first and foremost rule before system generation
is attempted involves getting a .SCOM printout ($S J to the Monitor) and a .DAT slot printout ($RJ
to the Monitor) in order to assist in determining two basic elements in the system; (1) skip chain content
and order; and (2) • DAT slot assignments.

5.4.2.1

DECtape or DECtape/Disk Systems
An 8K, non-EAE, non-API, KSR33 DECtape system is sent to all DECtape or DECtape/Disk

customers. Each customer with a core configuration of greater than 8K or who has either EAE or API
or a KSR35 Teletype will want to go through system generation in order to tailor his installation for
maximum efficient use. All customers who, upon examining the .SCOM printout, discover devices or
options listed that are not present in their system may want to eliminate the irrelevant skips from the
chain. Those with non-standard devices (A/D, for example) will want to expand the chain.
Listed below is the skip chain as it appears in the standard 8K DECtape system:
SPFAL
DTDF
DSSF
DRSF
MTSF
LSDF
RCSF
RCSD
CLSF

Power Fail
DECtape Done
Disk Done
Drum Done
Magneti c Tape Done on Error
Line Printer Done
Card Column Ready
Card Done
Clock Done

5-15

RSF
PSF
KSF
TSF
DTEF
MPSNE
MPSK
SPE
*DRNEF

Ready Done
Punch Done
Keyboard Done
Teleprinter Done
DECtape Error
Non-Existent Memory Reference
Memory Protect Violation
Memory Pari ty Error
Drum No Error

It is important that the above order remain intact even if deletions or additions are to be
made.

For example, given a PDP-9 without the Power Fail, Parity or Memory Protect options and

having either card reader, line printer or magnetic tape, the skip chain should be generated as follows:
DTDF
DSSF
CLSF
RSF
PSF
KSF
TSF
DTEF
The position of a skip to be added to the chain varies with the nature of the device.
example, high data rate devices might best be placed at the top of the chain.

For

Listed below are the. DAT slot assignments as they appear in the standard 8K DECtape system:
.DAT

DEVICE

USE

-15
-14
-13

DTA2
DTA1
DTB2
HAO
DTBl
HAO
DTCO
NONE
NONE
DTC2
HAO
HAO
DTCO

OUTPUT
INPUT
OUTPUT
LISTING
INPUT
INPUT
SYSTEM DEVICE FOR. SYSLD
OUTPUT
EXTERNAL LIBRARY FOR • LOAD
SYSTEM INPUT
TELEPRINTER OUTPUT
KEYBOARD INPUT
SYSTEM DEVICE FOR. LOAD

-12
-11

-10
-7

-6
-5
-4
-3
-2
-1

*DRNEF, Skip on drum error flag not raised, is a good example of a negative skip, i.e., a skip on a
flag not being raised. When specifying such a skip to • SGEN, a minus sign must precede the skip.
It sh~d be carefully noted that negative skips should only be included when the device is physically
present in the PDP-9 system since the skip lOT otherwise becomes an effective NOP causing execution
of the next instruction which is a JMP to the Monitor error routine (lOPS 3).

5-16

1
2

3
4
5
6
7
10

DTAO
DTAl
DTA2
TTAO
PRAO
PPBO
DTAl
DTA2

USER
USER
USER
USER
USER
USER
USER
USER

The following examples are variations on • DAT slot assignments* as a function of either core
size or different peripherals.
a. Given an 8K system with line printer and card reader: LPA should be assigned to . DAT
slot -12 and one of the positive slots, for example, 3, 7, or 10. CDB should be assigned to one of
the positive slots.
b.
be as follows:
-15
-14
-13
-12

-11
-10
-7

-6
-5

-4
-3
-2
-1

1
2
3

4
5
6

7
10

Given a 16K (or greater) Disk/DECtape system, a suggested list of assignments might

DKA6
DKA4
DKA5
TTA
DKA4
PRA
DKCO
DKA5
NONE
DKAS
TTA
TTA
DKAO
DKA4
DKAS
DKA6
TTA
PRA
PPA
DTAl
DTA2

c. Given a 16K (or greater) DECtape system with magnetic tape, a suggested list of assignments might be as follows:
-15
-14
-13
-12

-11

DTA2
DTAl
DTA2
TTA
DTAl

* All installations with 16K or more core should assign the ~ versions of handlers to all .DAT slots.

5-17

-10

-7
-6
-5
-4
-3
-2
-1

1
2

3
4
5
6
7
10

5.4.2.2

PRA
DTCO
DTA2
NONE
DTA2
HA
HA
DTAO
DTAO
DTAl
DTA2
HA
PRA
PPA
MTFl
MTF2

Paper Tape/Disk Systems
Three trays of paper tapes {24} representing an SK, non-EAE, non-API, KSR33 Disk system

are sent to all disk customers who do not have DECtape. Installations with greater than 8K, API, EAE,
KSR35 or non-standard options will want to generate a system after the initial loading of their 8K system.
The discussion about skip chain order appearing in Section 5.4.2.1 {DECtape/Disk system}
applies and should be read carefully.
Usted below are the. DAT slot assignments as they appear in the standard 8K Paper Tape/
Disk system:
.DAT

DEVICE

USE

-15
-14
-13
-12

DKA6
DKA4
DKB5
HAO
DKB4
HAO
DKCO
NONE
NONE
DKC5
HAO
HAO
DKCO
DKA4
DKA5
DKA6
HAO
PRAO
PPAO
DKAl
DKA2

OUTPUT
INPUT
OUTPUT
LISTING
INPUT
INPUT
SYSTEM DEVICE FOR. SYSLD
OUTPUT
EXTERNAL LIBRARY FOR. LOAD
SYSTEM INPUT
TELEPRINTER OUTPUT
KEYBOARD INPUT
SYSTEM DEVICE FOR. LOAD
USER
USER
USER
USER
USER
USER
USER
USER

-11
-10
-7
-6
-5
-4
-3
-2
1
1
2
3
4
5
6
7
10

5-1S

The following example is a variation of • OAT slot assignments* as a function of both increased core size and additional peripherals:
Given a 16K system with line printer, card reader and magnetic tape, a suggested list of
assignments follows:
-15
-14
-13
-12

DKA6
DKA4
DKA5
LPA
DKA4
PRA
DKCO
DKA5
NONE
DKA5
TTA
TTA
DKAO
DKA4
DKA5
DKA6
TTA
PRA
PPA
CDB
MTF1

-11
-10
-7
-6
-5
-4
-3
-2
-1
1
2
3

4
5
6
7

10
5.4.3

Assigning Devices
Before calling a system or user program, the user should make all device assignments

necessary to the program(s) to be run.
The ASSIG N command (see Section 5.3.2.8) is used to attach hardware devices to the slots
of the device assignment table. Figure 5-1 shows the normal setup of . OAT. Only system slots -2, -3,
and -7 cannot be modified by the ASSIGN command, since these must be used by the Monitor.
System programs use the negative .DAT slots while user programs should use the positive .DAT
slots. PIP-9 (Peripheral Interchange Program) is an exception to this rule in that it uses all the positive
.DAT slots (1 through 10) and system slot -2, -3 for Teletype I/O.
.DAT Slot
.DATBG

Device Handler*

-15

DTA

-14

DTA

-13

DTB

Unit

Use

Output (EDITOR, UPDATE, CONVERTER,
SYSGEN)
Input (EDITOR, UPDATE, CONVERTER,
SYSGEN, DUMP)

Output (MACRO-9, FORTRAN IV)

*AII installations with 16K or more core should assign the A version of handlers to all • OAT slots.

5-19

.DAT

-12

TTA

Listing {MACRO-9, FORTRAN IV, UPDATE,
DUMP, CONVERTER}

-11

DTB

Input {MACRO-9, FORTRAN IV}

-10

PRA

Input {DDT}
Secondary Input {EDITOR, UPDATE,
MACRO-9, SYSGEN}

-7

DTC

-6

PPC

Output (DDT)

-5

NONE

External Library {Linking Loader}

-4

DTC

-3

TTA

Tel epr inter Output

-2

TTA

Keyboard Input

-1

DTC

System Device {System Loader}

Input (Linking Loader)

}

All
system
programs

System Library {Linking Loader}

.DAT
1
2

DTAO
DTAl
DTA2
TTA
PRA
PPB
DTAl
DTA2

3
4
5

6
7
10

User
and
PIP-9
.DAT slots

.DATND=.
Figure 5-1
5.4.4

Function of .DAT Slots in Keyboard Monitor System

Loading Programs in the Keyboard Monitor Environment
In the Keyboard Monitor environment, all system programs are called by unique keyboard

commands {F4, MACRO, etc.}. User programs are called by loading the Linking Loader or DDT {via
LOAD, GLOAD, DDTNS, or DDT commands} and requesting it to load the desired program. In loading
user programs, the main program is loaded first, followed by all required subprograms. By loading subprograms in the order of size {largest first, smallest last}, the user has a better chance of satisfying core
requirements for his programs in systems with extended core memory. {See Figure 5-2 for memory maps
of programs loaded in the Keyboard Monitor system.}
When a keyboard command requests a new system program, the Keyboard Monitor loads the
System Loader and the system device handler into core. The System Loader is basically the Linking
Loader in absolute form and always requires the same device handler to acquire input from the system
device. The Linking Loader, on the other hand, is relocatable and device independent.

*See Section 7.4 for a description of the handlers.

5-20

The System Loader is used to bring in all system programs, including the linking Loader, and
their associated device handlers. Once loaded, the linking Loader is used to bring in user programs,
their subroutines and device handlers.
The System Loader can print the same error messages as the linking Loader (see Appendix D),
except that it precedes the error code with the symbol. SYSLD. It returns control to the System Bootstrap to re-initialize the Keyboard Monitor if an error occurs.
Once a system program is loaded by the System Loader, the loaded program assumes control.
At this stage, it is ready to accept an input command string from the keyboard telling it how to proceed.
Detailed operating procedures for each system program are given in the Keyboard Monitor Guide
(DEC-9A-MKFA-D) •

5.4.5

Error Detection and Handl ing
Comprehensive error checking is provided by the Keyboard Monitor, the loaders, and the

Input/Output Programming System. Detailed lists of errors that may occur are given in Appendices C,
D, and E, respectively. After error messages are output, the user may optionally restart the system or
user program, dump core, or return control to the System Bootstrap for re-initialization of the Keyboard
Monitor (see Section 5.3.2.11). If QDUMP has been issued prior to execution of this program, an
automatic CTRL Q (dump the current job, in core image, onto prespecified blocks of the system device)
takes place before control is returned to the System Bootstrap. The number of the unit to be used as
the dump device must be typed by the user after the error typeout. This dumped file can be selectively

I is ted by the system Dump program. If HALT has been typed prior to program execution, the program
stops after error message typeout allowing manual memory cell examination, manual restart or core
dump.

5-21

MEMORY MAP B

MEMORY MAP A
BK or 16K or

8K or 16K or
24K or 32K

24K or 32K
RESIDENT
SYSTEM
BOOTSTRAP

RESIDENT
SYSTEM
BOOTSTRAP

• SCOM AND eSCOM+3

f - - - - - - - I e SeOM

NON-RESIDENT
KEYBOARD MONITOR:
INITIALIZATION AND
KEYBOARD COMMAND
DECODER

• SCOM +1 AND. SCOM +2

RESIDENT
KEYBOARD MONITOR
(INCLUDING
TELETYPE
HANDLER)

The System Bootstrap loads {DUMP mode}
the Keyboard Monitor {resident and nonresident} from the system device.

The System Bootstrap is loaded via
the paper tape reader in HRM mode.

Figure 5-2 Keyboard Monitor System Memory Maps

5-22

MEMORY MAP C

MEMORY MAP D (SYSTEM PROGRAM IS NOT LINK ING LOADER)

8K or 16K or

8K or 16K or
24K or 32K

24K or 32K
RESIDENT
SYSTEM
BOOTSTRAP

R£SIDENT
SYSTEM
BOOTSTRAP

•

SCOM

• SCOM
SYSTEM
PROGRAM

SYSTEM
LOADER

1-------SYSTEM
DEVI CE
HANDLER

•

SCOM+3

SYSTE M
PROGRAM
TABLE SPACE
ie: MACRO-9
AND FORTRAN IV
SYMBOL TABLES.

• SCOM+2

SYSTEM PROGRAM
DEVICE HANDLER

SYSTEM PROGRAM
DEVICE HANDLER
•

SCOM+I a • SCOM+2

• SCOM+I

RESIDENT
KM-9
(INCLUDI NG
TELETYPE
HANDLER)

RESIDENT
KM-9
(INCLUDING
TELETYPE
HANDLER)

960 10

The Keyboard Monitor loads (DUMP mode)
the System Loader and the system device
handler from the system device
The System Loader, during loading of a
system program from the system devi ce ,
builds the loader (GLOBAL) symbol table
down from • SCOM+3 and the programs up
from. SCOM+2.

The System Loader learns which I/o handlers
are required by the requested system program
from its table of .IODEV info for system programs, loads the handlers relocatably just
above the resident KM-9 and then modifies
the System Bootstrap to bring in the system
program in Dump mode just below the Bootstrap.
• EXIT from the system program takes the process
back to Memory Map B where the system bootstrap reinitializes the Keyboard Monitor.
Refer to Section 7.4 for the sizes of the device
handlers that may be associated with the. DAT
slots used by the System program.

Figure 5-2 Keyboard Monitor System Memory Maps (Cont)

5-23

MEMORY MAP
8K

or 16K or

MEMORY MAP F (NOT DDT OR DDTNS)

E (SYSTEM PROGRAM IS LINKING LOADER)
LOAD
GLOAD

BK or 16K or
241< or 32K

OOT

24K or 32K

DDTNS
CHAIN

RESIDENT
SYSTEM
BOOTSTRAP

• SCOM B

RESIDENT
SYSTEM
BOOTSTRAP
•

• SCOM+3

SCOM

USER
PROGRAM(S)

USER DEVICE
HANDLER
USER DEVICE
HANDLER
USER DEVICE
HANDLER
• SCOM +3

• SCOM+2

LINKING LOADER
OR CHAIN

-------

LINKING LOADER
DEVICE
HANDLER
{
LINKING LOADER
DEVICE
HANDLER

(bl

LINKING LOADER
DEVICE HANDLER

REFER TO SECTION
4.6 FOR DEVICE
HANDLER SIZES.

------LINKING LOADER
DEVICE HANDLER
(0.)

• SCOM+l

RESIDENT
KM-9
IINCWDING
TELETYPE
HANDLER)

RESIDENT
KM-9
IINCLUDING
TELETYPE
HANDLER)

The System Loader learns which I/O handlers
are required by the Linking Loader, loads them
relocatably and then loads the Linking Loader
relocatably.

• EXIT from user program takes the process back
to Memory Map B where the system bootstrap
re-initial izes the Keyboard Monitor.
Refer to Section 7.4 for sizes of device handlers.

If a DDT load, the Linking Loader just prior to
giving control to DDT moves the DDT symbol
tab Ie down in core so that it overl ays a II of the
Linking Loader except for the small routine that
makes the· block transfer.
The Linking Loader, during loading of user
programs down from .SCOM+2, builds the loader (GLOBAL) and DDT (if DDT) symbol tables up
from .SCOM+2. DDT symbol table will not be
built if a LOAD, GLOAD, or DDTNS load.

.SCOM+l and .SCOM+2 both point to one of two
places and non-BLOCK DATA COMMON (FORTRAM IV or MACRO-9) output may make use of
core as low as they point.
a. If the user program did not have any device
handlers in common with the Linking Loader.
b. If the user program did have at least one device
handler in common with the Linking Loader.

Figure 5-2 Keyboard Monitor System Memory Maps (Cont)

5-24

MEMORY MAP H (EXECUTE)

MEMORY MAP G (DDT OR DDTNS)
8K or 16Kor

8K or 16K or

24Kor32K

24K or 32K

RESIDENT
SYSTEM
BOOTSTRAP

• SCOM

• SCOM
EXECUTE

(600\0

DDT

USER
PROGRAM( S)

USER
PROGRAM(S)

USER/DDT
DEVICE HANDLER

LIBRARY
PROG R AM(S)

USER/DDT
DEVICE HANDLER

USER DEVICE
HANDLER(S)
•

46(0

SCOM+ 3
NAMED COMMON

•

SCOM+3

DDT CREATED
SYMBOLS AND
PATCH SPACE
• SCOM + 2
DDT (USER)
SYMBOL
TABLE

'/////1///1//1/,
LINKING LOADER
DEVICE HANDLER
LINKING LOADER
DEVICE HANDLER

B LANK COMMON

• SCOM +(

• SCOM+2
LINKING LOADER
BLOCK TRANSFER
ROUTINE

EXECUTE'S

DE V ICE
HANDLER

RESIDENT
KM-9
(INCLUDING
TELETYPE
HANDLER)

RESIDENT
KM- 9
(INCLUDING
TELETYPE
HANDLER)

. EXIT from the user program takes the process back The System Loader loads the I/O handler needed by
EXECUTE above the resident portion of the Monitor.
to Memory Map B where the system bootstrap reIt then modifies the System Bootstrap to bring in
initializes the Keyboard Monitor.
EXECUTE in dump mode just below the Bootstrap.
Refer to Section 7.4 for sizes of device handlers.
When the user typed in the name oftheXCTfile to be run,
Non-BLOCK DATA COMMON (FORTRAN IV)
the non-resident portion of the Monitor stored the fi Ie
or MACRO-9 output) may make use of core as
name in .SCOM + 7, 10 and 11. . EXECUTE now
low as the DDT symbol table *. However,
locates this file and brings in the first chain.
trouble will occur if the user requests DDT to
create symbols or make patches that cause overFORTRAN programs pass on data in blank common
starting at . SCaM + 2. Macro programs pass on
laying of the COMMON area.
data between . SCO M + 2 and . SCO M + 3.
The Linking Loader device handlers would have
A call from the running chain to bring in another chain
been used to satisfy user device requests.
is effected by transferring control back to Execute.
*There is no DDT symbol table if a DDTNS load.
. EXIT from the user chain takes the process back to
PHASE 2 where the System Bootstrap re-initializes
the Keyboard Monitor.
Figure 5-2

Keyboard Monitor System Memory Maps (Cont)

5.5

BATCH PROCESSING
The Batch Processor portion of the Monitor allows user commands to come from the paper tape

reader or card reader instead of the Teletype, allowing many programs to be run without operator intervention. All Monitor commands read on the batch device are echoed on the Teletype. Monitor commands that are peculiar to the Batch Processor include the following:
Function

Command
BATCH (B) dv

Enter Batch mode with dv as batch device; dv can be
typed as
PR, for paper tape reader,
or CD, for card reader
NOTE
The following special characters can be keypunched using the indicated card codes.
Back arrow (-) = 0-5-8 punch
ALT MODE (ESC) = 12-1-8 punch

$JOB

Used to separate jobs (the loading of any system or user
program constitutes a single job).

$ DATA

Beginning of data - all inputs up to $END are not
echoed on the Teletype.

$END

End of data.

$ EXIT

Leave Batch mode.
NOTE
The following commands are illegal when operating in Batch mode: QDUMP, HALT, GET
(all forms), BATCH, LOAD, DDT, and DDTNS.

Special Batch Processor control characters include the following:
CTRL T (echos tT)

Skip to next job.

CTRL C (echos tC)

Leave Batch mode.

To use the Batch Processor, proceed as fo I lows •
a.

Load the batch tape or deck into the batch device.

Type BATCH (or B) dv on the keyboard, where dv is PR or CD.

When operating in Batch mode, the Keyboard Monitor has the following operational changes.
a. Any ASSIGN command that references the batch device (any handler) will be assigned
to the batch device handler.

5-26

Any REQUEST command will print the batch device handler PR* or CD* (whichever

applies) .
c. When the non-resident Monitor is reloaded, it interprets batch communication bits in
the top register of core (177777, 377777, 577777, or 777777):
Bit 0
Bit 1

1 = Batch mode

o = Non-Batch mode
1 = $JOB command in

0= Search for $JOB
Bit 2

1 = CD is batch device

0= PR is batch device
When an error occurs in a job, the non-resident Monitor is reloaded and the Batch Processor
skips to the next $JOB command on the batch device.
The following example was produced under control of the Batch Processor. Underlined commands are on paper tape.

ALT MODE termination is indicated with a

$tC
M·Jf'-J I TOR VLj8
$BATCrl PR
This command causes all subsequent commands
to come from the paper tape reader.

MOl\! I TOR VLtB
$$JOB TEST BATCH
$PIP
PIP V7A
>N DKLt
>T DKLt TEST SRC (A)
$DATA
$!<..ND

The entire program to be compiled below appears on the paper tape between $DATA and
$END.

MONITOR \jLjB
S) $JOB

s)ASSIGN TT -12
s)R FLt
• W1T

DEVICE

USE

- 13

DXAS
TTA0
DKALt
TTA0
PR*0

OUTPUT
LI STIi\! G
INPUT
CONTROL AND ERRDR MESSi1GES
COMMAND STRII\!G

-12
- 11
-3

-2
SiFLt

5-27

FO RT R:';,\) 4 'v 4A
> S~ L~ B<-TEST®
E,\) 0 PASS 1
C
C

TEST OF BATCrl

PRJCESSO~

FORTRAN program to I ist numbers from
1 through 10.

1 I = 1 ~ 10

~~ITE

100

FO~ivJiH

(4~100)

(6X~I3)

STO? 12345
E,\)O

TEST
•1
I
• F '.~
• 100
• FE
.FF
· ST
Fe>

17777
00012
00043
00036
00021
00037
00040
00041
00042

*
*
*
*
* · .

Mel.\) I TOR VLJB
S$JJ3
$ GLO.40

L,)ADER 'v3A
>TEST ®
TEST
37573
BCOID
34600
STOP
34565
SPMSG
34472
FIOPS
33736
OTSER
33642
REAL
32654

Program execution begins here.

2
3
4

5
6
7
8
9

5-28

STOP

012345

MOI\JITOR VLJ8
$$JOB
$$EXIT

MONITOR V48

5.6

Control is returned to Teletype at this po int.

DECTAPE FILE ORGANIZATION
DECtape can be treated either as a non file-oriented medium or as a fi Ie-oriented medium,

as described in the following paragraphs.
5.6. 1

Non-File-Oriented DECtape
A DECtape is said to be non-file-oriented when it is treated as magnetic tape by issuing the

MTAPE commands: REWIND, BACKSPACE, followed by .READ or .WRITE. No directory of identifying
information of any kind is recorded on the tape. A block of data (255 10 word maximum), exactly as
presented by the user program, is transferred into the handler buffer and recorded at each. WRITE command, where the final (256 th) word is the data link to the next DECtape block of data. A .CLOSE
terminates recording with a simulated end-of-file consisting of two words: 001005, 776773. The data
link of this EOF DECtape block is calculated in case another file is to be recorded. Note that the
simulated end-of-file is identical whether executing a .CLOSE in a file-oriented or non-file-oriented
environment.
Because braking on DECtape allows for tape roll, staggered recording of blocks is employed
in the PDP-9 ADVANCED Software System to avoid constant turnaround or time-consuming back and
forth motion of sequential block recording. When recorded as a non-fi Ie-oriented DECtape, block 0 is
the first block recorded in the forward direction. Thereafter, every fifth block is recorded until the
end of the tape is reached, at which time recording, also staggered, begins in the reverse direction.
Five passes over the tape are required to record 576 10 blocks (0-10778 ),
5.6.2

Fi Ie-Oriented DECtape
Just as a REWIND command declares a DECtape to be non-fi Ie-oriented, a • SEEK or • ENTER

implies that a DECtape is to be considered file oriented. The term file-oriented means simply that a
directory containing file information exists on the DECtape. A directory listing of any DECtape so recorded is available via the (L}ist command in PIP or the (D)irect command in the Keyboard Monitor.
A fresh directory may be recorded via the (N)ewdir command in the Keyboard Monitor or PIP or by the
5-29

N or S switch in PIP.
The directory of all DECtapes except system tapes occupies all 4008 cells of block 1008 , It is
divided into two sections: (1) a 408 word Directory Bit Map and (2) a 3408 word Directory Entry Section.
The Directory Bit Map defines block availability. One bit is allocated for each DECtape
block (576 10 bits = 3210 words). When set to 1, the bit indicates that the DECtape block is occupied
and may not be used to record new information.
The Directory Entry Section provides for a maximum of 56 10 files on a DECtape (24 10 on a
system tape). A four-word entry exists for each file on DECtape, where each entry includes the 6-bit
trimmed ASCII file name (6 characters maximum), and file name extension (3 characters maximum), a
pointer to the first DECtape block of the file, and a file active or present bit.
On a system tape on Iy the first 2008 words are used as a 24 fi Ie directory. Cells 0-378
constitute the System Tape Directory Bit Map and cells 40-1778 contain 24 fi Ie Directory Entry Section.
The second 2008 words of DECtape block 1008 contain basic system directory information (blocks
occupied by system programs), used by KM-9, PIP-9 and SGEN-9.

DECTAPE DIRECTORY

Block 0

ooEE;--- Directory

Block 1077
Entry
_ 0_

"""---- _

Bit Map

_ _ _ ooEE;-_ _ Directory

Entry
Section

'------------Entry 55 10

377

A DIRECTORY ENTRY

5 6

11 12
File

Wd. 0

Name
2

Fi Ie Name Extension
1

Data Li nk (Next Fi Ie Block)
Sign Bit: 1 = Fi Ie Active

5-30

17
Note: Nulls (0) fi II in
short fi Ie names. A fj Ie
name extension is not
absolutely necessary.

Additional file information is stored in blocks 71 through 77 of every file-oriented DECtape
(blocks 71 through 73 of a system tape). These are the File Bit Map Blocks. For each file in the directory, a 408 word File Bit Map is reserved in block 71 through 77 as a function of file name position in
the Directory Entry Section of block 100. Each block is divided into eight File Bit Map Blocks. A
File Bit Map specifies the blocks occupied by that particular file and provides a rapid, convenient
method to perform DECtape storage retrieval for deleted or replaced files. Note that a file is ~
deleted until the new one of the same name is completely recorded, that is, on the .CLOSE of the new

file.

Fi Ie Bit Map Blocks

Block 71

File Bit Map for File 0

File 7
Block 72

Fi Ie 15 10

Block 77

File 48 10

File 55 10

When a fresh directory is written on DECtape, blocks 71 through 100 are always indicated
as occupied in the Directory Bit Map.
Staggered recording (at least every fifth block) is used on file-oriented DECtapes, where the
first block to be recorded is determined by examination of the Directory Bit Map for a free block. The
first block is always recorded in the forward direction; thereafter, free blocks are chosen which are at
least five beyond the last one recorded. When turnaround is necessary, recording proceeds in the same

5-31

manner in the opposite direction. When reading, turnaround is determined by examining the data link.
If reading has been in the forward direction, and the data link is smaller than the last block read, turnaround is required. If reverse, a block number greater than the last block read implies turnaround.
A simulated end-of-file terminates every file and consists of a two word header (1005,
776773) as the last line recorded. The data link of this final block is 777777.
Section 2.3.1 of this manual discusses lOPS data modes. Data organization for each I/O
medium is a function of these data modes. On file-oriented DECtape there are two forms in which data
is recorded: (1) packed lines - lOPS ASCII, lOPS binary, Image ASCII and Image binary and (2) dump
mode data - Data Mode.
In lOPS or image modes, each line (including header) is packed into the DECtape buffer.
A 2'5 complement checksum is computed and stored for each line of information. When a line is encountered which will exceed the remaining buffer capacity, the buffer is output, after which the new
line is placed in the empty buffer. No line may exceed 254 10 words, including header, because of the
data link and even word requirement of the header word pair count. An end-of-file is recorded on a
.CLOSE. It is packed in the same manner as any other line, that is, if the buffer will not contain it,
the line goes into the next free block chosen.
In dump mode, the word count is a Iways taken from the I/o macro. If a word count is specified which is greater than 255 10 (note that space for the data link must be allowed for again), the DECtape handler will transfer 255 10 word increments into the DECtape buffer and from there to DECtape.
If some number of words less than 255 10 remain as the final element of the dump mode .WRITE, they
will be stored in the DECtape buffer, which will then be filled on the next .WRITE, or with an EOF if
the next command is .CLOSE. DECtape storage use is thus optimized in dump mode since data is stored
back to back without headers.

5.7

INTERIM DISK SYSTEM
The PDP-9 Interim Disk System (Storage Unit RB09 and Disk Control RC09) is an adaptation

of the PDP-9 ADVANCED Software System for DECtape and includes the Keyboard Monitor, all PDP-9
ADVANCED Software System programs, a disk system bootstrap, disk handlers DKA, DKB, DKD, and
DKC, and either DSKSAV or DSKPTR, utility programs to save and restore disk data to/from DECtape
or paper tape, respect i ve Iy •
In the interim system, the disk is treated as six logical units (0,1,2,4,5,6), each conta i n i ng 576 10 b locks of 256 10 words per block. Si nce each of the RB09 di sk tracks conta i ns 80 sectors
of 64 10 words, a track is equivalent to 20 logical DECtape blocks. The table below lists unit-track
correspondence:

5-32

Track, Sector (Inclusive)

Disk Unit
DKO

0,0-28,63

DK1

30,0-58,63

DK2

60,0-88,63

DK4

100,0-128,63

DK5

130,0-158,63

DK6

160,0-188,63

The minimum hardware configuration required for the PDP-9 Disk System is a basic PDP-9
(8K, Teletype, high-speed reader/punch), RB09 Disk Unit with Disk Control RC09, and Direct Memory
Access Channel Multiplexer Adapter, Type DM09A.
5.7.1

The Disk as System Device
The PDP-9 ADVANCED Software System resides on tracks

through 28 (Disk Unit 0) with the

Keyboard Monitor starting at tracks 0, sector 0. All absolute system programs, directory and File Bit
Map information occupy the same logical block positions on disk as they occupy on DECtape. Blocks on
tracks

through 28 not used for system storage are avai lable for user fi les provided that the disk protec-

tion switches have not been activated. It is recommended however, that once the disk system is loaded,
the protection switches be activated for tracks

through 29.

Much of the description on DECtape file organization (Section 5.4.1), applies to the Interim
Disk System as well, since the four disk handlers (DKA, DKB, DKD, and DKC) are modified versions of
DECtape handlers DTA, DTB, DTD, and DTC.

5.7.2

Disk File Organization
In the interim system the PDP-9 Disk is divided into 6 units (each equivalent to a DEC tape

in length) therefore, each unit has its own directory of files.

Each unit, each directory and the file

therein is treated as distinct within the system.
Disk files may be recorded in anyone of the five standard PDP-9 ADVANCED Software System data modes. MTAPE .READS, .WRITES may be considered as creating a sixth data mode as far as
data organization of MTAPE files on Disk is concerned.
Disk file data organization may take one of three forms:
a.

Packed lines: lOPS ASCII, lOPS Binary, Image Alphanumeric, Image Binary

Packed dump areas: Dump Mode

MTAPE transfers

5-33

In lOPS or Image modes, lines, including headers, are packed back to back on a logical
words or 4 disk sectors). A 2 1s complement checksum is computed by the disk handler
10
and stored in the header of each line. When a line is encountered which will exceed the current block

disk block (256

capacity, that line is placed in the next free logical disk block. A data link to the new block is stored
in the final word of the filled block. Unused space in any file block is equal to zero. The final line
of the file, whatever the data mode, is an EOF header of two words: 1005, 776773. The data link of
the last block of any fi Ie except a • MT APE transfer is 777777.
In Dump Mode, the transfer word count is a Iways taken from the I/o Macro. If a word count
greater than 255 10 is specified (again the last word of a logical block must contain a data link), the disk
handler will transfer 255 10 word increments onto the disk in linked logical blocks. If some number of
words less than 255 10 remain as the final element of the Dump Mode. WRITE, they will be stored on the
next logical disk block which will then be filled on the next .WRITE or with an EOF if the next command
is .CLOSE.

Disk storage is optimized in Dump Mode since data is packed and no headers are used.

An MTAPE • WRITE causes transfer of a 255 10 word logical disk block starting at logical
block 0 of the specified disk unit. A disk unit used for MTAPE transfers contains no directory information.

No packing is performed by the disk handler, it is the user1s responsibility to format the record

in whatever way he chooses. When a .CLOSE is issued, the usual EOF line is recorded as the last block
of an MTAPE file. The data link is computed in case another MTAPE file is to be written and is stored
in the EOF (or last) block of the present file.

5.S

DISK SYSTEM OPERATION
Operation of the PDP-9 Disk System is essentially the same as operation of the DECtape sys-

tem. To begin disk system operation, the paper tape Disk Bootstrap (.DKSBT) is loaded into core memory (HRM: 17637) and automatically loads the Keyboard Monitor into core from disk track O. (The
bootstrap restart address is 17646.)
PDP-9 ADVANCED Software for the disk is distributed as an SK system in one of two forms:
a.

1 DECtape

3 trays (24 10 ) of paper tapes

}

SK, non-API, non-EAE,
KSR33 systems

DSKPTR is the utility program for loading the disk system from paper tape, a 30 minute operation. It is additionally capable of loading or punching any logical disk unit or 6K elements thereof
as a function of ACS settings on the PDP-9 console.
The data format of tapes generated or loaded via DSKPTR is shown in Figure 5-3.

Each tape

consists of 6K or 24 logical 256 10 word sequential disk blocks. Each data block on paper tape is preceded by six blank frames to aid visual identification.

5-34

FRAME 0-2

BLOCK #

\0-1077)

BLOCK N
FRAME 3- 5 . BLOCK CHECKSUM"

BLANK

BLOCK N+I

256 BINARY DATA WORDS

"BLOCK CHECKSUM ~ 2'S COMPLEMENT
CHECKSUM OF BLOCK J!'+DATA WORDS

Figure 5-3

5.8. 1

Paper Tape Block Format

Paper Tape Load Procedure
a.

Place the paper tape of DSKPTR in reader with address switches set to 17720.

Press I/o RESET and READI N.

c.
on teletype.

When the program is loaded, it wi II display its title, DSKPTR and skeleta I directions
SET:

*ACSO=O
ACS15-17 = Unit #

Paper tape to disk
0,1,2,4,5,6

Place the first disk system tape in reader and press CONTINUE.

e. IIHIT CONTINUE FOR NEXT TAPE II will be typed on the teletype when the tape has
been read correctly. Load the remaining 23 tapes in a similar fashion. Note, any number of tapes up
to the fu II 24 may be loaded in any order.
The following errors may be displayed on the teletype during loading:
1.

Unit Error: ACS15-17 = 3 or 7.
Action:

Reset ACS15-17 = 0, 1,2,4,5,6

Press CONTINUE

Reload Tape: Reader end-of-tape condition at illegal point.
Action:

Reload tape

Press CONTINUE

Input Checksum Error: Block checksum incorrect.
Action:

Reload tape from beginning, OR position tape to the front
of block in error, or leave tape in current position.*

*ACS 0-17 = 0 for full system load onto disk.

5-35

Press CONTINUE

When the disk system is loaded, set the write protect switches for tracks 0 through 29.

Load the Disk Bootstrap into the reader with address switches set to 17637.

h. Press I/o RESET and READIN. The PDP-9 Keyboard Monitor will be loaded from the
disk and will type:

$ MONITOR
The system is now ready for operation. Refreshing all user disk unit directories is imperative
at this point. This is done with the KM-9 Newdir (N) command, for example,

$ N 1J
refreshes disk unit 1. This command should be issued for units 1, 2, 4, 5, and 6 before further operation.
DSKPTR may also be used to punch out 6K areas of the disk. To do so, follow steps a. and b.
above under loading procedure.
c.

ACSO=l
ACS15-17 = Unit #
**ACS5-14 = Logical Block # 0, 30, 60 .••• 10508

Press CONTINUE

See step e. above.

The following errors may be displayed on Teletype during disk to punch output:
1.

Unit Error: (See loading procedure)

Reload Tape: Punch out of tape
Action:

Reload punch

Press CONTINUE

Splice Tape

Disk Error: Probably parity error. AC will contain disk status. Look at disk control panel for AC bit meaning.
Action: Since OSKPTR will have tried 8 times to read disk
a.

Reset at 16000 or

Press CONTINUE to accept data.

*Oata block in error will be accepted as is.
**ACS5-14 = 0 causes punching of all 2410 tapes for disk unit (ACS15-17). ACS5-14 = NON 0 causes
punching of one 6K paper tape starting at the logical block specified. Note, this feature is particularly
useful when PATCH is used for system program modification and a single back up paper tape of the associated disk area is desired. See Appendix F for program location on disk.

5-36

5.B.2

Disk System Generation
Once the Disk System is loaded and disk un its have been refreshed, it may be necessary to

generate a system more appropriate to the needs of the installation.

For example, since the released

system is an BK system, all 16, 24 and 32K installations will want to generate a system for the appropriate core size.
Operation of SGEN (PDP-9 System Generator Program) is described in Section 5.4.2 of this
manual and in the Keyboard Monitor Guide (DEC-9A-MKFA-D). Disk unit 0 should be assigned to • DAT
slot -10 and -14. The output device (presently disk unit 6) appears in .DAT slot -15.
When system generation has been completed, PIP-9 should be called into memory to copy
disk unit 6 onto disk unit 0 from which the new system may now be operated. The PIP command to be
used is
C DKO (H) +- DK6J
DSKPTR may be used to produce a backup of the system on paper tape.

5.B.3

Disk System Generation from DECtape
The PDP-9 installations with both disk and DECtape receive the standard Keyboard Monitor

system on DECtape. It is an BK system which when loaded from DECtape, unit 0 with the DECtape
bootstrap (I/O RESET followed by READIN with the address switches set to 17637) allows a disk system
to be generated.
Once the Monitor is in from DECtape and has typed:
MONITOR

$
the REQUEST and SCOM commands should be issued to the Monitor for system information and the following I/o handler assignments should be made:
$A DTAO-10 ,-14/DKDO-15 ~
System Generator shou Id then be ca II ed:
$SGEN J
Once disk system generation is complete, the write protect switches for tracks 0 through 29 shou Id be
activated.
The Monitor system may now be loaded from disk unit 0 using the Disk Bootstrap (HRM: 17637).
When the Monitor is in core, it is imperative to refresh all user disk unit directories. This is done with
the Keyboard Monitor Newdir (N) command, for example,
$N q
refreshes disk unit 1. This command should be issued for units 1, 2, 4, 5, and 6, before further operation.

5-37

5.8.4

Disk System Save/Load from DECtape
Once a disk system has been generated, it is valuable to produce a backup system for DEC-

tape for rapid disk system restoration when necessary.
DSKSAV is the utility program for saving or loading the PDP-9 ADVANCED Software Disk
System to/from DECtape. System loading or saving with DSKSAV is a 55 second operation. It is
additionally capable of loading or saving on DECtape, any other logical disk unit as a function of ACS
settings on the PDP-9 console. The save/load procedure is as follows:
a. Place paper tape of DSKSAV in reader with address switches set to 17720.
(Restart = 16000)
b.

Press I/o RESET and READIN.

c. When the program is loaded, it will type its title, DSKSAV, and brief directions on the
console Teletype. The program is stopped to allow ACS settings.
Set: * ACSCFO
ACSO=l
ACS15-17=Unit#
d.
CONTINUE.

DECtape to Disk (LOAD)
Disk to DECT APE (SAVE)
0,1,2,4,5,6

Be sure the DECtape unit selection is identical to ACS 15 through 17 and press

The following errors may be displayed on the Teletype during loading:
1.

Unit Error: ACS15-17=30r7.
Action:

Disk Error:

Reset ACS 15-17 = 0, 1, 2, 4, 5, 6

Press CONTINUE

Probably illegal disk address (for example, attempt to load
disk with write protect switch enabled).
AC contains disk status. Examine disk control panel for AC
bit meaning.

Action:

Correct disk problem if possible and press CONTINUE.

DECtape Error:

Probably end zone error. AC contains DECtape status.
amine DECtape control panel for AC bit meaning.

Action:

If DECtape is in the forward end zone, press CONTINUE.

If DECtape is in the far end zone (beyond block 1077),
position tape out of end zone and press CONTINUE.

If parity or mark track error**, press CONTINUE to restart transfer from the beginning, or set ACSO through
17 = a and press CONTINUE to retry read one more time.

Ex-

DSKSAV may also be used to save or load other logical units of the disk. This has proved to
be very useful since it provides rapid DECtape backup of any or all disk data files. To do so, follow
steps (a) and (b) above under loading procedure.

* ACSO- 17= a for fu II system load onto di sk.
* * DS KAV w ill have tr i ed to read four times before the message.

5-38

5.9

ACSO = 1
ACS15-17 = Unit #

Press CONTINUE

See step e. under load procedure.

MAGNETIC TAPE SYSTEMS
PDP-9 ADVANCED Software provides for IBM-compatible magnetic tape as a file-structured

medium and as a full-scale system device. The magnetic tape handlers communicate with a single
TC-59 Tape Control Unit (TCU). Up to eight magnetic tape transports may be associated with one TCU;
these may include any combination of transports TU-20 and TU-20A. * At least two transports are required for full system operation.
There are a number of major differences between magnetic tape and other bulk-storage devices (for example, DECtape or Disk); these differences affect the operation of the device handlers.
Magnetic tape is well-suited for handling data records of variable length; such records, however, must
be treated in serial fashion. The physical position of any record may be defined only in relation to the
preceding record. Block-addressable devices are most economically used in transferring records having
fixed lengths that are hardware-constrained. Using such devices, the absolute physical location of any
record is program-specifiable. Because of the serial character of data blocks as they are recorded on
magnetic tape and because of the presence of blocks of unknown length, three techniques available in

I/o operations to block-addressable devices are not honored by the magnetic tape handlers:
a. The user cannot specify physical block numbers for transfer. In processing I/o requests
that have block numbers in their argument lists (. TRAN, for example), the handler ignores the blocknumber specification.
b. The only area open for output transfers in the file-structured environment is that following
the current logical end of tape. The exception to this rule is in the recording of the File Directory as
explained below.
c. Only a single file may be open for transfers (either input or output) at any time on a
single physical unit.

*A detai led description of the TCU is contained in the TC-59 Instruction Manual (DEC-9A-I3BA-D)
and in the PDP-9 User Handbook (F-95).

5-39

5.9. 1

Fi Ie Organization
The discussion below applies particularly to MTA, the most general and the largest of the

magnetic tape handlers. Response to data-mode specification is identical for handlers MTB., MTC.,
and MTD., except for the modes that are illegal in these more limited handlers. MTA. is a full device
handler that will read and write tape in both the file-structured and non-file-structured fashion. It
will honor all CAL functions and requests for transfer in all data modes. The characteristics of data
recorded on tape are dependent upon a decision as to the file structuring. This decision, in MTA., is
based upon much the same criteria as in other bu Ik-storage handlers. If the first I/o request after an
.INIT is .READ, .WRITE, or any .MTAPE command, the referenced unit is presumed to be non-filestructured. If the first request after an .INIT is .SEEK, .ENTER, .CLEAR, or .OPER, then the
referenced unit is treated as a file-structured device.

5.9. 1 .1

Non-Fi Ie-Structured Data Recordi ng - The treatment of data to be recorded or read in non-

file-structured fashion has two primary objectives. It is intended to satisfy the requirements of the
FORTRAN programmer whi Ie sti II providing the assembly language programmer maximum freedom in the
design of his tape format.
Magnetic tape data, written in the non-fi Ie-oriented environment, differs in two important
respects from data recorded by means of fi Ie-oriented I/o requests. In the first place, no handlersupplied supplementary information is written on the tape.

No reference is made, for example, to a

file directory, and block-control data (see below) is never written. Secondly, no blocking (or packing)
of lines is performed by the handler. Each .WRlTE (or .READ) request causes direct data transfer between the user's line buffer and the TCU. No buffering or editing of any kind is done (in lOPS and
Image modes) by MTA. Each .WRITE (or .READ) issued results, in general, in the transfer of exactly
one physical record to (or from) tape.*
5.9.1.2

File-Structured Data Recording - The programmer can make the fullest possible use of those

features peculiar to magnetic tape by employing non-file-oriented transfer techniques. On the other
hand, he has little recourse to the powerful file-manipulation facilities available in the system. Filestructured I/o brings to bear the whole body of file-system software, gives true device independence
to the magnetic-tape user, and allows extensive use of the storage medium with a minimum of effort.

*An exception to this rule is the Dump Mode transfer. The handler will pack output data into, and
extract input data from, an internal buffer in this mode.

5-40

5.9.1.3

Block Format - Every block recorded by MTA. (with the exception of end-of-file markers,

which are hardware-recorded) in file-structured mode includes a two-word Block Control Pair and not
more than 255 10 words of data.
The Block Control Pair serves three functions: it specifies the character of the block (label,
data, etc.), provides a word count for the block, and gives an lS-bit block checksum. The Block Control
Pair has the following format:
Word 1:
Bits 0 through 5: Block Identifier (BI). This 6-bit byte specifies the block type. Values of
BI may range from 0 to 77 S ' Current Legal values of BI, for all user files, are as follows:

BI Value

Block Type Specified

User-File Header Label
User-File Trailer Label

User-File Data Block

Bits 6 through 17: Block Word Count (BWC). This 12-bit byte holds the 2's complement of
the total number of words in the block (including the Block Control Pair).

Legal values of BWC range

from -3 to -40 lS .

Word 2:
Bits 0 through 17: Block Checksum. The Block Checksum is the full-word, unsigned, 2's
complement sum of all the data words in the block and word 1 of the Block Control Pair.

5 6

N TOTAL WORDS
IN BLOCK
N- 2 DATA
WORDS

[

Figure 5-4

Block Format, Fi Ie-Structured Mode

5-41

5.9.2

Fi Ie Identification and Location
One of the main file-manipulation functions of the handler is that of identifying and locating

referenced fi les. This is carried out by two means: first, names of fi les recorded are stored in a fi Ie
directory at the beginning of the tape; and second, labels integral to the file are recorded with the file
itself.

5.9.2.1

Magnetic Tape File Directory - The directory, a single-block file (and the only unlabeled

fi Ie on any fi Ie-structured tape), consists of the first recorded data block on the tape. It is a fixedlength block with a constant size of 257 10 words and the following characters:
a.

Block Control Pair (words 1 and 2)

Word 1:
Block Identifier = 748 = File Directory Data Block.
Block Word Count = 4018 = 73778.
Word 2:
Block Checksum: As described.
b. Active File Count (Word 3, Bits 9 through 17) 9-bit one's complement count of the
active file names present in the Fi Ie Name Entry Section (described below).
c. Total File Count (Word 3, Bits 0 through 8) 9-bit one's complement count of all files
recorded on the tape, including both active and inactive files, but exclusive of the file directory block.
d. File Accessibility Map (Words 4 through 17): The File Accessibility Map is an array of
25210 contiguous bits beginning at bit 0 of word 4 and ending as bit 17 of word 17. Each of the bits in
the Accessibility Map refers to a single file recorded on tape. The bits are assigned relative to the
zeroth fi Ie recorded; that is, bit 0 of word 4 refers to the first fi Ie recorded; bit 1, word 4, to the
second file recorded; bit 0, word 6, to the 3710 file recorded; and so on, for a possible total of 25210
files physically present.
A file is only accessible for reading if its bit in the Accessibi lity Map is set to one.
A file is made inaccessible for reading (corresponding bit = 0) by a . DLETE of the file, by a .CLOSE
(output) of another file of the same name, or by a .CLEAR. A file is made accessible for reading (corresponding bit = 1) by a .CLOSE (output) of that file. Operations other than those specified above
have no effect on the File Accessibility Map.
e. File Name Entry Section (Words 18 through 257): The File Name Entry Section, beginning at word 18 of the directory block, includes successive 3-word file name entries for a possible
maximum of 80 entries. Each accessible file on the tape has an entry in this section. Entries consist
of the current name of the referenced file in standard DEB format: file name proper in the first two
words, extension in the third word; 6-bit trimmed ASCII characters, left-adjusted and, if necessary,
zero-fi II ed •
The position of a file name entry relative to the beginning of the section reflects the
position of its accessibility bit in the map. That bit, in turn, defines the position of the referenced
file on tape with respect to other (active or inactive) files physically present. Only active file names
appear in the entry section, and accessibility bits for all inactive files on the tape are always set to
zero; accessibility bits for all active files are set to one.
To locate a file on the tape having a name that occupies the second entry group in the
Fi Ie Name Entry Section, the handler must (a) scan the Accessibi lity Map for the second appearance
of a 1-bit, then (b) determine that bit's location relative to the start of the map. That location speci-

5-42

fies the position of the referenced file relative to the beginning of the tape. The interaction of the
File Name Entry Section and the Accessibility Map is shown in Figure 5-5.

BIT POSITION

BCP

{ WO,,,

WORO 2
FILE COUNTS

BEGINNING
OF TAPE

BLOCK CHECKSUM

WORD 3

FILE
D I RECTORY

WORD 4

FILE
ACCESSIBILITY
MAP

FILE #1
1I NACTIVEl
WORD 16
WORD 17
FILE ",2
(ACTIVEl

WORD 18

WORD 2 I
FILE #3
(lNACTIVEl

FILE
NAME
ENTRY
SECTION

WORD 24
FILE #4
(ACTIVEl

FILE #5
(ACTIVEl

WORD 257

END OF TAPE

Figure 5-5a. Format of the File Directory Data
Block, showing relationship of active and inactive
files to file name entries and to Accessibility Map.
5.9.2.2

Figure 5-5b. Format of file-structured tape,
showing directory block and data files.

User-File Labels - Associated with each file on tape are two identifying labels. The first is

a header label and precedes the first data block of the fi Ie; the second, a trai ler label, follows the
final recorded data block of the file. Each label is 27 10 words in length. Label format is shown in
Figure 5-6.
Note that the trailer label differs from the header label only in the contents of the BI field
and in that the former includes an indication rNord 4) of the total blocks recorded in the file. The
total includes the two labels themselves.

5-43

o
WORD'

5 6

7745

WORD 2

CHECKSUM

WORD 3

777 XXX

WORD 4

000000

F==

7745
CHECKSUM
777 XXX

FILE NAME

+NBLOCKS

WORD 5

l
WORD27'O~
L-______________________l
WORD 26'0

5 6

RESERVED

~---

RESERVED

Figure 5-6a. User-Fi Ie Header Label Format

5.9.2.3

Figure 5-6b. User-File Trailer Label Format

File Names in Labels - The handler will supply the contents of the file-name fields (Word 3)

in labels. These are used only for control purposes during the execution of • SEEK's. The name consists
simply of the two's complement of the position of the recorded file's bit in the Accessibility Map: the
"name" of the first file on tape is 777777; that of the third file is 777775; and so on. A unique name
is thus provided for each file physically present on the tape. Since there may be a maximum of 252 10
files present, legal file-name values lie in the range 777777 to 777404.
5.10

MAGNETIC TAPE SYSTEM OPERATION

5.10.1

System Fi Ie Structure
In general, the system tape differs only incidentally from the user tapes described previously.

Directories, labels, and data blocks have like formats and perform identical functions on both user and
system tapes. Some identifying information however, is different in order to accommodate those cases
in which the tape is bootstrap-accessed (for example, in loading the System Loader).

5.10.1.1 System File Labels - Labels on the system tape serve the same purpose as user-file labels;
that is, the identification of the file which follows. They differ only in the contents of the Block Identifier field and of the file name indicator. For header labels, BI = 368 ; for trailer labels, BI = 378 ,
The file-name words in both labels contain the block number which begins the file in block-addressable
bulk-storage system. In all other respects, the labels are identical to those which appear on user tapes.
Typical system tape label format (for PIP) is shown below.

5-44

5 6

WORD I

WORD 2

310636

WORD 3

000671

WORD 4

000000

P'P"F'LE NAME"

a" E?oooooo =l

WORD 27,0 _ 0 0 0 0 0 0

5 6
37

1745
CHECKSUM *

i--- ~

'0"'

17
7745

000671

P'P "FILE NAME"

+N BLOCKS

TOTAL BLOCKS
IN PIP

RESERVED
(ZEROES)

* 400636 +C (WORD 4)

Figure 5-7a.

System Program (PIP) Header Label.

Figure 5-7b.

System Program (PIP) Trailer Label.

All absolute system programs are labeled in the manner described.

5.10.1.2 System File Data Blocks - The Block Control Pair for an absolute system program block serves
a purpose somewhat different from that for a user-fi Ie data block. The format of the Block Control Pair
is as follows:
a.

Block Identifier \Word 1, bits 0 through 5): 778 = System program data block.

b. Word Count \Word 1, bits 6 through 17): Two's complement count of data words in the
block, including the Block Control Pair.
c.

5.10.2

Word 2: 15-bit load address-l for this block.

System Tape Organization
The system tape is organized in the usual fashion, that is, the File Directory data block is

recorded first and is followed by labeled data files. The single requirement is that two system files the Monitor and the System Loader - appear immediately following the Directory. Other system fi les
are recorded following the System Loader.

5.10.3

System Startup
The system tape must be mounted on unit 0 and the transport must be on line and ready. The

bootstrap program is loaded via the paper tape reader; the bootstrap will bring the Monitor into core
from the system tape and give control to it. The user may then proceed as described in Section 5.4.

5-45

5.10.4

Continuous Operation*
Under certain circumstances, it is possible to perform successive I/o transfers without in-

curring the shut-down delay that normally takes place between blocks. The handler stacks transfer
requests, and thus ensures continued tape motion, under the following conditions:
a. The I/o request must be received by the CAL handler before a previously-initiated I/o
transfer has been completed.
b.

The unit number must be identical to that of the previously-initiated I/o transfer.

c. The previously-requested transfer must be completed without error. In general, successive error-free READS (WRITES) to the same transport wi" achieve non-stop operation. The examples
given below illustrate the principle.
Example 1: Successive Continued Operation.
SLOT = 1
INPUT = 0
BLOKNO = 0
READ 1
READ2
RETURN

. TRAN SLOT, INPUT, BLOKNO, BUFF1, 257
.TRAN SLOT, INPUT, BLOKNO, BUFF2, 257
JMP READ1

The program segment in Example 1 will most probably keep the referenced transport (.DAT
slot 1) up to speed. The probab i Iity decreases as more ti me e lapses between READ 1 and READ2 I and
between READ2 and RETURN.
Example 2: Unsuccessful Continued Operation.
SLOT = 1
INPUT = 0
BLOKNO = 0
READ
STOP
RETURN

. TRAN SLOT, INPUT, BLOKNO, BUFF, 257
.WAIT SLOT
JMP READ

The program segment in 'Example 2 will not keep the tape moving because the explicit .WAIT
at location STOP prevents control from returning to location READ until the transfer first initiated at
READ has been completed.
Example 3: Unsuccessful Continued Operation
SLOTl = 1
SLOT2 = 2
INPUT = 0
BLOKNO = 0

*Control and transport requirements for successful continuous operation are outlined in the TC-59
Instruction Manual (DEC-9A-I3BA-D) and in the PDP-9 User Manual (F-95).

5-46

READ1
READ2
RETURN

• TRAN SLOTl, INPUT, BLOKNO, BUFF1, 257
. TRAN SLOT2, INPUT, BLOKNO, BUFF2, 257
JMP READ1

This program segment will not provide non-stop operation because of the differing unit
specification at READ 1 and READ2.

5.11

DRUM FILE ORGANIZATION
Drum handlers DRA, DRB, DRC, and DRD are now available in version V4B of the Keyboard

Monitor System. The Drum handlers are modified versions of DECtape handlers DTA, DTB, DIC, and
DTD, (see Section 7.4) and permit data transfer to/from the RM09 Drum by both user and system programs.
It should be clearly noted, however, that availability of Drum handlers does not imply use of the Drum
as a system device; that capabi lity does not presently exist.
The PDP-9 Advanced Software Drum handlers may be used with anyone of the five RM09
drum options available. Storage capacity is defined in the following table in terms of DECtape storage
capacity.

Drum

Size

Number
of Units

Number
of Blocks (256 10)

32K

1/4

128

65K

1/2

256

131K

512

256K

1024

524K

2048

A Drum unit is defined as 512 10 sectors or blocks of 256 10 words each (i .e., 64 blocks less
than the capacity ofa single PDP-9 DECtape). The 32,65 or 131K Drums are referenced as unit 0;
the 262K drum, as units Oand 1; the 524K drum, as units 0,1,2, and 3. Referencing a unit number
greater than that permitted for a given drum results in an lOPS 26 error. Listed below are the sector
limits for each unit of each Drum.

5-47

Unit Sector Limits

~
Drum

32K

o - 177

---

65K

0-377

---

131K

0-777

---

262K

0-777

1000 - 1777

---

527K

0-777

1000 - 1777

2000 2777

3000 3777

The drum size of a system must be set up in .SCOM+4, bits 15-17. A value of 1-5 is used
where 1 = 32K; 2 = 65K, etc. lOPS 35 results if . SCOM+4 is not properly set for drum size.
Although the Drum control is designed to perform full block (256 10) transfers rather than
variable word count transfers, code has been included in both DRA and DRD to allow variable word
count transfers via the . TRAN command (i.e., . TRAN works for Drum as it does for the PDP-9 Disk
and DECtape). Furthermore, division of the Drum into logical units does not prevent. TRAN's or
. MT APE READS/WRITES from referencing any and all Drum sectors provided drum unit 0 is used. More
simply, if drum units 1-3 are referenced, a check is made such that ~ transfer is a IIowed to exceed the
sector limits of a unit. If sector size exceeds 7778 , an lOPS 25 error message results. However, if
Drum unit 0 is assigned, any sector may be referenced in . TRAN or . MTAPE READ/WRITE commands,
provided the physical drum size is not exeeded.
Drum file data organization is basically the same as that for DECtape (see Section 5.6).
As mentioned earlier, the file capacity is limited by a unit size of 512 10 rather than 576 10 . Sector
100 (1100 for unit 1, etc .), contains the Drum unit directory; sectors 71-77 (1071 - 1077 for unit 1,
etc.), contain fi Ie bit map information. Unit size is reflected in a directory listing via PIP. For
example, when the N (NEWDIR) command is issued, the listing appears as follows:
32K Drum:
DIRECTORY LISTING

o USER FILES

710 SYSTEM BLKS
170 FREE BLKS

5-48

65K Drum:
DIRECTORY LISTING

o USER FILES

510 SYSTEM BLKS
370 FREE BLKS
131, 262 or 524K Drum: (each unit)
DIRECTORY LISTING
USER FILES
110 SYSTEM BLKS
770 FREE BLKS

Because the Drum is not used as a system device, it should be noted that t Q to the Drum
cannot be executed. Consequently, the S switch in PIP is inoperative to the Drum and results in execution of the N (NEWDIR) command instead.
Users of Monitor V4B (9-30-68) system tapes wi II find the Drum handlers included in their

I/o library and the skip chain set up accordingly. To adopt the system for the installation Drum size,
however, .SCOM+4 (absolute location 104), bits 15-17, must be set (1-5) by use of the system program,
PATCH.
Drum users with Monitor tapes earlier than V4B must perform the following sequence:
1.

Use SGEN to generate a new system tape being sure to:
a. Answer "yes" when asked about the presence of new handlers (DRA, DRB,
DRC and DRD.)
b.

Answer DRSF, 706101 and
DRNEF, 706201
to the new skip lOT question.
c.

Position DRSF high in the skip chain (after DTDF - DECtape or DSSF - Disk).

d. Position - DRNEF as the very last skip in the chain. Note: DRNEF is a
reverse skip (SKIP ON NOT ERROR) and must be preceded by a minus (-) sign.
2. Use UPDATE to incorporate the new Drum handlers into the library of the newly
generated tape.
3.

Use PATCH to set .SCOM+4, bits 15-17 (absolute cell 104) in KM9 to the appropriate

drum size (1-5) for the installation.

5-49

CHAPTER 6
BACKGROUND/FOREGROUND MONITOR

6.1

BACKGROUND/FOREGROUND MONITOR FUNCTIONS
The Background/Foreground Monitor is designed to control processing and I/O operations in

a real-time or time-shared environment. It is essentially an extension of the Keyboard Monitor (described in Chapter 5) and allows for time-shared use of a PDP-9 by a protected, priority, user FOREGROUND program and an unprotected system or user BACKGROUND program.
The Background/Foreground Monitor greatly expands the capabilities of PDP-9 ADVANCED
Software and makes optimum use of all available hardware. It allows for recovery of the free time (or
dead time) that occurs between input/output operations, and promotes 100% utilization of central processor time.
The reader is referred to Chapter 2 for a general discussion of the Monitor environment, and
to Chapter 3 for a detailed description of user program commands (system macros) available in the Background/Foreground Monitor environment. It should be noted that all material presented in this manual
for the Background/Foreground Monitor is preliminary and subject to change.
FOREGROUND programs are defined as the higher-priority, debugged user programs that
interface with the real-time environment. They normally operate under Program Interrupt (PI) or Automatic Priority Interrupt (API) control, and are memory protected. At load time they have top priority
in selection of core memory and I/O devices, and at execution time they have priority (according to
the assigned priority levels) over processing time. Depending upon system requirements, the user IS
FOREGROUND program could be an Executive capable of handling many real-time programs or subprograms at four levels of priority (with API present).
BACKGROUND processing is essentially the same as the processing normally accomplished
under control of the Keyboard Monitor. That is, it could be an assembly, compilation, debugging run,
production run, editing task, etc.

BACKGROUND programs may use any facilities (for example, core,

I/O, and processing time) that are available and not simultaneously required by the FOREGROUND
job. Using the Monitorls Batch processing capability optimizes the processing of BACKGROUND jobs
under control of the Background/Foreground Monitor.
The Background/Foreground Monitor system is externally a keyboard-oriented system; that
is, all FOREGROUND and BACKGROUND requests for systems information, core, I/O devices, programs to be run, etc., are made via the Teletype keyboards (see Figure 6-1). At run time, the Monitor
internally controls scheduling and processing of I/O requests, while protecting the two resident users.

6-1

FOREGROUND JOB CONTROL UNIT

MULTI STATION

L - - - - - - l T~~~~~7L ~g~~~S~L
OR LTl9A/ LTt9B(S)

PDP-9

MULTI-UNIT

TE LE TYPE
HANDLER
(WHICH IS
PART OF THE
RESIDENT
MON I TORI

BACKGROUND JOB CONTROL UNIT

Figure 6-1

Keyboard Communication in Background/Foreground
Monitor System

The Background/Foreground Monitor performs the following functions as it controls the timeshared use of the PDP-9 central processor by two co-resident programs:
a.

Schedules processing time.

Protects the FOREGROUND job's core and I/O devices.

c. Provides for the sharing of multi-unit device handlers, such as DECtape, by both FOREGROUND and BACKGROUND jobs.
d.

Allows convenient use of API software levels by FOREGROUND jobs.

Provides for convenient and shared use of the system Real Time Clock.

f.
Allows communication between the BACKGROUND and FOREGROUND jobs via coreto-core transfers.

6. 1• 1

Scheduling of Processing Time
At run time, the FOREGROUND job retains control except when it is I/O bound; that is,

when completion of an I/O request is required before it can proceed any further, as in the following
example.

6-2

.READ 3,O,LNBUF,48

/READ TO • DA T SLOT 3

• WAIT 3

/NAIT ON .DAT SLOT 3

If the .WAIT is reached before the input requested by the . READ has been completed, control is transferred to a lower priority FOREGROUND segment or to the BACKGROUND job unti I the input for the
FOREGROUND job is completed.
Since multi-unit device handlers can be shared by FOREGROUND and BACKGROUND programs, there is a mechanism by which a FOREGROUND I/o request will cause a BACKGROUND I/o
operation to be stopped immediately so that the FOREGROUND operation can be honored. On completion of the FOREGROUND I/o, the BACKGROUND I/o will be restarted with no adverse effects on
the BACKGROUND job.
The FOREGROUND program can also indicate that it is I/O bound by means of the .IDLE
command (Section 3.3.3). This is useful when the FOREGROUND job is waiting for real-time input
from anyone of a number of input devices, as in the following example (see Section 3.3. 1 for description of real-time read. REALR command).
.REALR 1,O,LNBUF1, 32, CTRLl, N

/REAL

• REALR 2,2, LN BUF2, 42, CTRL2, N

/TIME

.REALR 3,3, LNBUF3, 36, CTRL3, N

/READS

• IDLE

If the .IDLE is reached before any of the input requests have been satisfied, control is transferred to
a lower priority FOREGROUND segment or to the BACKGROUND job, which retains control until one
of the FOREGROUND input requests is satisfied. Control is then returned to the FOREGROUND job
by executing the subroutine at the specified completion address (CTRLl, CTRL2, CTRL3) and at the
priority level specified by N, which may be

= Mainstream (lowest level)
4 = Current level
5 = Software level 5
6 = Software leve I 6
7 = Software level 7

6-3

NOTE

If real-time reads (.REALR), real-time writes (REALW),
or interval timer requests (. TIMER) are employed in the
BACKGROUND, N may be set to 0,4,5,6, or 7,
but will be converted to 0 since the BACKGROUND
job can run only on the mainstream level. This allows
you to set up N as you want it to be in cases where a
BACKGROUND program is to be subsequently run in
the FOREGROUND.

6. 1.2

Protection of FOREGROUND Job Core and I/O
The FOREGROUND jobls core is protected by means of the Memory Protection Option (Type

KX09A). The BACKGROUND job runs with memory protect enabled; the FOREGROUND job runs with
memory protect disabled to allow for execution of lOT's.
Protection of the FOREGROUND jobls I/O devices is accomplished with the hardware by
means of the memory protect option, which prohibits lOT and Halt instructions in the BACKGROUND
area; and with the software by means of the Monitor and lOPS, which screen all I/O requests made by
Monitor CALIs. Also, the Linking Loader prevents the BACKGROUND job I/O from conflicting with
that of the FOREGROUND job (for example, it would not honor a BACKGROUND request for a paper
tape handler being used by the FOREGROUND job).

6.1.3

Sharing of Multi-Unit Device Handlers
The Background/Foreground Monitor allows sharing of multi-unit, mass-storage device

handlers (such as DECtape, Magnetic Tape, and Disk) between BACKGROUND and FOREGROUND
jobs to reduce core memory requirements for the system. Using these multi-unit handlers, n files can
be open simultaneously, where n equals the number of .DAT slots associated with the particular bulk
storage device. When this count is not true (because of the .DAT slots not being used simultaneously),
the keyboard command FILES (Section 6.3.1) can be used to remedy the situation.

Both the FORE-

GROUND and BACKGROUND jobs can indicate their file requirements by means of the FILES keyboard
command.
The multi-unit handlers are capable of stacking one BACKGROUND I/o request. Thus,
control is returned to the BACKGROUND job to allow non-I/O related processing when the handler is
preoccupied with an I/O request from the FOREGROUND job. For example, if the FOREGROUND job
has requested DECtape I/O with a .READ, and is waiting for its completion on a .WAIT, control is returned to the BACKGROUND job. If the BACKGROUND job requests DECtape I/o with a . READ, the

6-4

handler wi II stack the request and return control to the BACKGROUND job following the . READ. The
BACKGROUND job can then continue with non-I/O related processing as though the. READ were being
honored.

6.1.4

Use of Software Priority Levels
The Background/Foreground Monitor allows convenient use of software priority levels of the

API by the FOREGROUND job. The BACKGROUND job can use only the mainstream level.

6.1.5

Use of Real-Time Clock
The Background/Foreground Monitor provides for convenient and shared use of the system

real-time clock. It will effectively handle an unlimited number of intervals at the same time, thus
the real-time clock can be used simultaneously by both BACKGROUND and FOREGROUND jobs.

6.1.6

Communication Between BACKGROUND and FOREGROUND Jobs
The Background/Foreground Monitor allows communication between BACKGROUND and

FOREGROUND jobs via core-to-core transfers. This is accomplished by means of a special "I/O device" handler within lOPS. Complementing I/O requests are required for a core-to-core transfer to
be effected; for example, a FOREGROUND .READ (.REAlR) from core must be matched with a BACKGROUND .WRITE (.REALW) to core.
Two possible uses of this feature are:
a. The BACKGROUND job could be related to the FOREGROUND job, and as a result of
its processing, pass on information that would affect FOREGROUND processing.
b. The BACKGROUND job could be a future FOREGROUND job, and the current FOREGROUND job, being its predecessor, could pass on real-time data to create a true test environment.

6.2

HARDWARE REQUIREMENTS AND OPTIONS
The following hardware is required to operate the Background/Foreground Monitor System.
a.

Basic PDP-9 with Teletype,

Memory Extension Control, Type KG09A,

Additional 8192-Word Core Memory Module, Type MM09A,

Memory Protection Option, Type KX09A,

6-5

External Teletype System, including at least*;
(1)

One Teletype Control, Type LT09A,

(2) One Teletype Line Unit, Type LT09B,
(3) One Teletype, Model KSR33 or equivalent,
f.

Bulk Storage System, comprising either;
(1)

One DECtape Control, Type TC02, and two DECtape Transports, Type TU55, or

(2)

One Di sk System, Type RB09, or

(3)

One Disk System, Type RF09/RS09

The following options may be added to improve system performance (as noted);
Effect

Options
Additional 8192 Word Core Memory
Modules, Type MM09B and MM09C

Increase the maximum size of both BACKGROUND and FOREGROUND programs
that can be handled by the system.

Automatic Priority Interrupt, Type
KF09A

Allows for quicker recognition of requests
for service by FOREGROUND devices.

Extended Arithmetic Element, Type KE09A

Increases speed of arithmetic calculations

Additional DECtape Transports, Type TU55,
or IBM-compatible Magnetic Tape Transports, Type TU20 or TU20A

Allows greater bulk storage capability,
simultaneous use of storage media by more
programs. Since only one file may be open
at a time on IBM-compatible magnetic
tape transports, more then two Type TU20
or TU20A transports may be desirable for
some applications.

Automatic Line Printer, Type 647

Provides greater listing capabilities.

200 CPM Card Reader, Type CR03B

Allows card input and control cards for
BACKGROUND Batch processing.

Additional Teletype Line Units, Type
LT09B, (or LTl9B) and Teletypes, Type
KSR33 or equivalent

Provides additional output devices if
multiple FOREGROUND jobs may require
simultaneous output or BACKGROUND
jobs wish to use multiple devices.

*The basic system Teletype is assigned to the BACKGROUND environment. One Teletype of the
external Teletype system must be reserved for the FOREGROUND job(s); additional Teletypes may be
assigned to either BACKGROUND or FOREGROUND functions. If the API option is avai lable, a
Type LTl9A Teletype Control and a Type LT19B Line Unit are required.

6-6

6.3

KEYBOARD COMMANDS
In addition to the keyboard commands available in the Keyboard Monitor environment

(see Section 5.3), the Background/Foreground Monitor recognizes and accepts the following commands:
FILES, FCORE, FCONTROL, and BCONTROL. Each of these commands is described in the following
paragraphs.

6.3. 1

FILES
This command is used to conserve core space by indicating the number of bulk storage files

that will be open simultaneously. It is normally typed prior to requesting the loading of user programs
so that the system or linking loader can allocate sufficient buffer space. The command is typed after
the Monitor's dollar sign request.
Example:
$FILES DT3
In this case, the DECtape handler will be able to accommodate three files open simultaneously.

6.3.2

FCORE
This command is used to define additional core required by the FOREGROUND job, exclu-

sive of the Monitor, the system device handler, the teletype handler and the FOREGROUND user
programs. The command is normally typed following the Monitor's dollar sign request and is only applicable before loading the FOREGROUND job. It is followed by a space and some octal number n,
which represents the total number of 1K octal increments of core memory required by the FOREGROUND
job (area between .SCOM+2 and .SCOM+3). If FCORE is not used, core will be allocated dynamically
at load time and there will be no free core available to the FOREGROUND job.
Example:
$FCORE

6.3.3

FCONTROL
This command allows the user to change the Teletype assigned to the FOREGROUND job

while the Monitor is operating in the FOREGROUND mode. Initially, keyboard commands are accepted from external Teletype Unit 1. The user could assign external Teletype Unit 2 (if available)
to the FOREGROUND job by typing "FCONTROL

2" after the Monitor's dollar sign request. The

Monitor would respond by typing CONTROL RELINQUISHED on external Teletype Unit 1, typing
MONITOR

6-7

on external Teletype Unit 2, and accepting subsequent keyboard commands in the FOREGROUND mode
from external Teletype Unit 2. Control would then remain with Teletype Unit 2 until another FCONTROL
is given.

6.3.4

BCONTROL
This command allows the user to change the Teletype assigned to the BACKGROUND job

while the monitor is operating in the BACKGROUND mode. When control is first transferred to the
BACKGROUND mode, keyboard commands are accepted from Teletype Unit 0 (basic system teletype).
The user can assign an external Teletype to the BACKGROUND job, provided that an external Teletype not currently assigned to the FOREGROUND job is available. For example, if external Teletype
Unit 2 is available and not assigned to the FOREGROUND program, the user could assign it to the
BACKGROUND job by typing "BCONTROL

2" after the Monitor's dollar sign request. The Monitor

would respond by typing CONTROL RELINQUISHED on Teletype Unit 0, typing
MONITOR

$
on Teletype Unit 2, and accepting subsequent keyboard commands in the BACKGROUND mode from
external Teletype Unit 2. Control would then remain with Teletype Unit 2 until another BCONTROL
is given.

6.4

OPERATING THE BACKGROUND/FOREGROUND MONITOR SYSTEM
The reader is referred to the Keyboard Monitor Guide {DEC-9A-MKFA-D} for detailed

operating procedures for system programs, which can be used in BACKGROUND processing. The
following PDP-9 ADVANCED Software System manuals contain additional detailed information on
system programs.
Manual

Document No.

Uti I ity Programs

DEC-9A-GUAB-D

MACRO-9 Assembler

DEC-9A-AMZA-D

FORTRAN IV

DEC-9A-KFZA-D

This section contains descriptions of loading the Background/Foreground Monitor, assigning
devices, loading user FOREGROUND programs, loading system or user BACKGROUND programs, and
error detection and handling. Figure 6-2 contains complete memory maps and a summary of all loading
procedures.

6-8

6.4.1

Loading the Background/Foreground Monitor
The procedure for loading the Background/Foreground Monitor is similar to that for loading

the Keyboard Monitor. That is, the System Bootstrap (in hardware READIN format) is loaded at the top
of core using the paper tape reader. This is accomplished by placing the tape in the reader, momentarily pressing the tape feed button, setting the Address switches to the lowest address of the bootstrap (37637 for 16K systems), and depressing the I/O RESET and READIN switches. The System Bootstrap automatically loads the resident portion of the Monitor from the system device into lower core.
It then transfers control to the Monitor via the .EXIT command, with the FOREGROUND flag set to
simulate a FOREGROUND. EXIT. (This will cause subsequent keyboard commands to be accepted
from Teletype Unit 1 and interpreted as FOREGROUND requests.) The resident Monitor loads the
non-resident Monitor from the system device into upper memory, overlaying the System Bootstrap. It
then types
MONITOR

$
on external Teletype Unit 1 and transfers control to the Keyboard Listener portion of the non-resident
Monitor to await keyboard commands from Teletype Unit 1. Initially, since the FOREGROUND flag
was set, these commands are interpreted as FOREGROUND commands. While operating in the FOREGROUND mode, the FOREGROUND control Teletype can be changed from external Teletype Unit 1
to any other external Teletype available by means of the FCONTROL keyboard command (see Section
6.3.3).

6.4.2

Assigning Devices
Before loading a user FOREGROUND program or a system or user BACKGROUND program,

the user should make all device assignments required for the program to be run. There are two Device
Assignment Tables (.DAT) in the Bockground/Foreground Monitor system: one used by BACKGROUND
jobs, and one used by FOREGROUND jobs. The Monitor determines which table is intended or required
according to its current operating mode. The. DAT slot assignment for BACKGROUND jobs are the
same as normal Keyboard Monitor. DAT slot assignments (see Section 5.4.3). Since only user programs
operate in the FOREGROUND mode, all .DAT slots can be used by the FOREGROUND job, except
.DAT slots -1, -4, -5 and -7.

6.4.3

Loading User FOREGROUND Programs
When a keyboard command that requests loading of a user FOREGROUND program is en-

countered, the non-resident Monitor brings in the System Loader, overlaying itself. This is done via

6-9

the resident system device handler. For FOREGROUND loads, the System Loader is the Linking Loader.
It first loads any other I/O handlers required for loading, and then loads the user program along with
its required I/O handlers. It then allocates buffer space to accommodate the n\:lmber of bulk-storage
files either
a.

specified by the keyboard command FILES that was typed prior to the load request, or

determined from the number of • OAT slots associated with bulk storage devices.

The System Loader sets the memory protect bound above the FOREGROUND system. It then
places the address of a routine to perform a .EXIT into the BACKGROUND program counter register
(control will go there when the FOREGROUND job becomes I/O bound), and gives control to the
FOREGROUND job with memory protect disabled.
When the FOREGROUND job becomes I/O bound, control is transferred to the routine which
performs a • EXIT. The Monitor recognizes this as a BACKGROUND .EXIT and loads the non-resident
Monitor (via the resident system device handler) into upper memory. It then gives control to the Keyboard Listener which types
MONITOR
$
on the system Teletype Unit 0 and then waits for BACKGROUND keyboard commands from the system
Teletype (Unit 0). While operating in the BACKGROUND mode, the control Teletype can be changed
from Unit 0 to any other Teletype available, not currently being used by the FOREGROUND job, by
means of the BCONTROL command (see Section 6.3.4).

6.4.4

Loading System or User BACKGROUND Programs
When a keyboard command that requests loading of a system or user BACKGROUND program

is encountered, the non-resident Monitor brings in the System Loader, overlaying itself. This is done
via the resident system device handler.
If the BACKGROUND program is a system program, the System Loader loads the system program I/O handlers up from the top of the FOREGROUND system*, allocates buffer space to accommodate all • OAT slots associated with bulk storage devices, and then loads the system program into the
top of memory. It then sets the memory protect bound above the allocated buffer space and transfers
control to the system program.

*The System Loader loads I/O handlers required by either a system program or the Linking Loader
just above the FOREGROUND job. This is done to make use of any space resulting from the fact
that the smallest unit of memory protection is 1K (decimal). Also, multi-unit handlers (such as
DECtape) which are already in core for the FOREGROUND job are shared, rather than loaded
again.

6-10

If the BACKGROUND program is a user program, the System Loader loads the Linking Loader
I/O handlers up from the top of the FOREGROUND system, allocates the required buffer space, and
then loads the relocatable Linking Loader where the memory protect bound can be set just below it.
The Linking Loader is used to load the user's BACKGROUND program down from the top of
core (see Keyboard Monitor Guide, DEC-9A-MKFA-D). The user's I/O handlers are loaded last (relocated to run from the area just above the Loaders I/O handlers). User program handlers that are
identical to Loader or FOREGROUND handlers already in core are not loaded. The necessary buffer
space is allocated just above the area where the user's handlers are to be relocated. An • EXIT from the
Linking Loader causes the user program I/O handlers to be block transferred to their running position,
the memory protect bound to be set just above the buffer area, and control to be transferred to the user
program.

6.4.5

End of Job
When an .EXIT is encountered in a job, • EXIT is output on the associated control Teletype

and additional action is taken depending upon whether the job is a BACKG ROUND or a FOREGROUN D.

If the job is a BACKGROUND, and the FOREGROUND job has not been completed, the
non-resident Monitor is loaded into upper core and outputs
MONITOR
$
to the current BACKGROUND control Teletype to indicate its readiness to receive BACKGROUND
commands. If the job is a BACKGROUND, and the FOREGROUND job has been completed, the
MONITOR

$
is output on the current FOREGROUND control Teletype to indicate readiness to accept FOREGROUND
commands.

If the job is a FOREGROUND, the FOREGROUND completion flag is set and control is
retumed to the BACKGROUND job. The BACKGROUND job may be aborted at this time by typing
CTRL C on the FOREGROUND control Teletype. This will cause ABORT to be typed on the current
BACKGROUND control Teletype, the non-resident monitor to be loaded into upper core, and
MONITOR
$
to be typed on the FOREGROUND control Teletype indicating readiness to accept FOREGROUND
command.

6-11

6.4.6

Error Detection and Handling
Comprehensive error checking is provided by the Background/Foreground Monitor, the

loaders, and the Input/Output Programming System. Detailed lists of errors that may occur are given
in Appendices C, D, and E, respectively.
After error messages are output, the non-resident Monitor is brought into core to allow
initialization of the next job.
The system programs that operate in the BACKGROUND mode also provide comprehensive
error checking. Refer to the appropriate PDP-9 ADVANCED Software System Manual (listed at the
beginning of this section) for detailed information on these errors.

6-12

MEMORY MAP A

MEMORY MAP B

16K r----S-Y-ST-E-M----~

16K

BOOTSTRAP

BK~----------~

SYSTEM
BOOTSTRAP

•

SCOM

•

SCOM +1 AND. SCOM +2

"RESIDENT
MON ITOR

o '--------------'

o
*INCLUDING MULTI-UNIT TELETYPE HANDLER
AND SYSTEM DEVICE HANDLER.

The System Bootstrap is loaded at the top of
core via the paper tape reader in HRM format.

Figure 6-2

The System Bootstrap automati ca lIy loads the
resident Monitor from the system device into
lower core.

Background/Foreground Monitor System Memory Maps

6-13

MEMORY MAP C

MEMORY MAP D
•

16K

16K . . . . . - - - - - - - ,

SCOM

NON-RESIDENT
MONITOR

• SCOM

SYSTEM LOADER

• SCOM +3

8K 1 - - - - - - - - 1

• SCOM+I AND. SCOM+2

• SCOM + 2 AND. SCOM + I

RESIDENT
MONITOR

o '---------'

The resident Monitor loads the non-resident
Monitor (via the resident system device
handler) into upper core, overlaying the
System Bootstrap

Figure 6-2

To load a user FOREGROUND program, the nonresident Monitor brings in the System Loader,
overlaying itself. For FOREGROUND loading,
the System Loader is the linking Loader.

Background/Foreground Monitor System Memory Maps (Cont)

6-14

MEMORY MAP E
16K

MEMORY MAP F
• SCOM

16K

SCOM

NON-RESIDENT
MONITOR

SYSTEM LOADER

• SCOM+3
ADDITIONAL LOADER
I/O HANDLERS
AND BU FFER
(IF NECESSARY!

8K
PROTECT BOUND.
'(f////////////// I-- MEMORY
(THE AREA BETWEEN THE BUFFER
BUFFER SPACE
USER PROGRAM
I/O HANDLERS

'/11IIIIIIULLIL

SPACE AND THE MEMORY PROTECT
BOUND IS DUE TO THE FACT THAT
THE 'SMALLEST UN IT OF MEMORY
PROTECTION IS IK DECIMAL.!

• SCOM +1,. SCOM+2
AND. SCOM + 25

FOREGROUND
SYSTEM

FOREGROUND
SYSTEM
USER PROGRAM (S!

RESIDENT
MONITOR

RES IDENT
MONITOR

The System loader first loads any additional
I/O handlers required for loading. It then
loads the user program and the I/O handlers
that it requires, and allocates buffer space.
Memory protect bound. (The area between
the buffer space and the memory protect
bound is due to the fact that the smallest unit
of memory protection is 1K decimal. However, this area can be used for dynamic data
storage via a software protect feature.)

Figure 6-2

When the FOREGROUND job becomes I/O bound,
control is transferred to the BACKGROUND job.
The resident Monitor loads the non-resident Monitor (via the resident system device handler) into
upper core. It then gives control to the Keyboard
listener (within the non-resident Monitor) to await
a BACKGROUND keyboard command.

Background/Foreground Monitor System Memory Maps (Cont)

6-15

MEMORY MAP H

MEMORY MAP G
16K

16K

• SCOM

SYSTEM LOADER

SYSTEM
PROGRAM

• SCDM+3

• SCOM+3

MEMORY
PROTECT
BOUND

--. fllllllll/llllll.

• SCOM +2

BUFFER SPA CE

'11/1/11/1/11/11.

}

• SCOM +1,. SCOM +2
AND. SCOM +25

BACKGROUND
I/O HANDLERS
• SCOM +1 AND. SCOM+25

FOREGROUND
SYSTEM

RESIDENT
MONITOR

When a keyboard command requests loading of
a BACKGROUND system or user program, the
non-resident Monitor brings in the System
Loader, overlaying itself.

Figure 6-2

If the BACKGROUND program is a system
program, the System Loader loads the system program I/O handlers up from the top
of the FOREGROUND system, allocates
buffer space, and loads the system program
at the top of core. It then sets the memory
protect bound above the buffer space and
gives control to the system program.

Background;1=oreground Monitor System Memory Maps (Cont)

6-16

MEMORY MAP I

MEMORY MAP "J

16K

o SCOM AND 0 SCOM +3

SYSTEM

o SCOM AND 0 SCOM +3

USER PROGRAM(S)

LOADER

USER PROGRAM
I/O HANDLERS

o SCOM+2

LINKING LOADER

MEMORY
PROTECT
BOUND

'11111111111,

"////////////,
BUFFER

BUFFER SPACE
BK

SPACE
o SCOM +1

oSCOM+1

LINKING LOADER
rio HANDLERS

BACKGROUND
I/O HANDLERS

o SCOM+25

FOREGROUND
SYSTEM

RE S IDENT
MONITOR

RESIDENT
MONITOR

If the BACKGROUND program isa user program,
the System Loader loads the Linking Loader I/O
handlers up from the top of the FOREGROUND
system, allocates buffer space, and loads the
Linking Loader such that the memory protect
bound can be set just below it.

Figure 6-2

The user's program, followed by its I/O handlers,
are loaded down from the top of core. The I/O
handlers are relocated to run just above the
Linking Loader I/O handlers so that the memory
protect bound can be set above them.

Background/Foreground Monitor System Memory Maps (Cont)

6-17

MEMORY MAP K
16K

• SCOM

USER PROGRAM( S)

• SCOM+3

MEMORY
PROTECT
BOUND

---. '1/////////////,

• SCOM+l AND. SCOM+2

BUFFER SPACE

•

USER PROGRAM
I/O HANDL E RS
BK
LINKING LOADER
I/O HANDLERS
• SCOM +25

FOREGROUND
SYSTEM

RESIDENT
MON ITOR

The. EXIT from the Linking Loader causes
the user program I/O handlers to be block
transferred to their running position, the
memory protect bound to be set i ust above
the buffer space, and control given to the
user program.

Figure 6-2

Background/Foreground Monitor System Memory Maps (Cont)

6-18

CHAPTER 7
I/O DEVICE HAN DLERS

This chapter contains information that is essential for a good understanding and proper use of
I/O device handlers for the I/o and Keyboard Monitor systems. Included is a general description of
I/O hardware and API software level handlers, a complete section on writing special I/O device handlers, a summary of I/O handlers acceptable to system programs, and a summary of standard I/O handler
features.
It is assumed that the reader is familiar with all related material in the PDP-9 User Handbook
(F-95), especially Chapter 9, Input/Output Considerations. It is also assumed that the reader is familiar with the PDP-9 Monitor environment and other pertinent information contained in this manual.

7.1

DESCRIPTION OF I/o HARDWARE AND API SOFTWARE LEVEL HANDLERS
This section applies to I/o and Keyboard Monitor environments only.

7.1.1

I/O Device Handlers
All communications between user programs and I/o device handlers are made via CAL in-

structions (see Chapter 3) followed by argument lists. The CAL Handler in the Monitor performs preliminary setups, checks on the CAL calling sequence, and transfers control via a JMP instruction to
the entry point of the device handler. When the control transfer occurs, the AC contains the address
of the CAL in bits 3 through 17 and bits 0, 1, and 2 indicate the status of the Link, extend mode and
memory protect, respectively, at the time of the CAL. Note that the content of the AC at the time of
the CAL is not preserved.
Or:! machines that have an API, the execution of a CAL instruction automatically raises the
priority to the highest software level (level 4). Control passes to the handler while it is still at level 4,
allowing the handler to complete its re-entrant procedures before debreaking (DBK) from level 4. This
permits the handler to receive re-entrant calls from software levels higher than the priority of the program that contained this call. If a device handler does not contain re-entrant procedures, system failure caused by inadvertent re-entries can be prevented by remaining at level 4 until control is returned
to the user.

If the non-reentrant method is used, the debreak and restore (DBR) instruction should be
executed just prior to the JMP* which returns control to the user, allowing debreak from level 4 and
restoring the conditions of the Link, extend mode, and memory protect. Any lOTs issued at the CAL
level (level 4 if API present, mainstream if no API) should be executed immediately before the

7-1

DBR
XCT
JMP*

.+1

exit sequence to ensure that the exit takes place before the interrupt from the issued lOT occurs. (The
XCT is necessary to ensure that the 3 cycles requested by the API on a debreak operation occur in the
instruction after the DBR.)
The CAL instruction must not be used at any hardware priority level (API or PIC), since
interrupts to these levels are not closed out by the execution of a CAL and recovery is not possible from
such sequences of events as
a.

An I/o flag coming up during a CAL at level 7,

Control going to the I/O device hand ler at level 3,

c. The handler at level 3 CALing and thus destroying the content of location 00020 for the
previous CAL.
The highest API software level {level 4} is also used for processing CALs and care must be
taken when executing CALs at this level. For example, a routine that is CAL'd from level 4 must know
that if a debreak (DBR or DBK) is issued, control will return to the calling program at a level lower than
4. The calling routine will also debreak; however, this second debreak will not be from level 4 but
from the next highest active level.

7.1.1.1

Setting Up the Skip Chain and API (Hardware) Channel Registers - When the Monitor is

loaded, the Program Interrupt Control (PIC) skip chain and the Automatic Priority Interrupt (API) channels are set up to handle the Teletype keyboard, teleprinter and clock interrupts, only. The skip chain
contains the other skip lOT instructions, but indirect jumps to an error routine result if a skip occurs, as
follows:
SKP DTA
SKP
JMP*INTl
SKP LPT
SKP
JMP*INT2
SKP TTl
SKP
JMP TELINT

/Skip if DECtape flag.
/INTl contains error address.
/Skip if line printer flag.
/INT2 contains error address.
/Skip if Teletype flag.
/To Teletype interrupt handler.

All unused API channels also contain JMPs to the error address.
When a device handler is called for the first time via an .INIT user program command, it
must call a Monitor routine (.SETUP) to set up its skip chain entry or entries and API channel, prior to
performing any I/o functions. The calling sequence is as follows.

7-2

CAL N

/N = API channel register 40 through 77 (see section
/7 .1.3 for standard channel assignments), 0 if de/vice not connected to API.
/. SETUP function code.
/Skip lOT for this device.
/Address of interrupt handler.

16
SKP lOT
DEVINT
(normal return)

DEVINT exists in the device handler in the following format.
DAC
LAC*
DAC
LAC
JMP
DEVINT JMP
DAC
LAC
DAC
10RS
SMA!CLA
LAW
TAD
DVSTON DAC
DEVCF
DEVION ION

DEVAC

DEVPIC

/SAVE AC.

AD--"-""", <

( DEVOUT \
""""--"""-;
DEVION
DVSTON
DEVPIC
DEVAC
DEVINT
DEVOUT
",

/SAVE PC, LINK, EX.MODE, MEM.PROT.
/FORCE ION AT DISMISSAL.

'",

/PIC ENTRY.
/API ENTRY, SAVE AC.
/SAVE PC, LINK, EX.MODE, MEM.PROT.
/CHECK STATUS OF PIC
/FOR RESTORATION AT DISMISSAL.
/PIC OFF, BUILD 10F lOT.
/PIC ON, BUILD ION lOT.

17740
DEVION
DVSWCH

/CLEAR DEVICE DONE FLAG
/ENABLE PIC SO THAT OTHER DEVICES
/AREN'T SHUT OUT.

10F
DEVIOT

/DISMISS ROUTINE
LAC
DAC
LAC
DVSWCH ION
DBR
JMP*

/DISABLE PIC TO INSURE
/DISMISSAL BEFORE INTERRUPT
/FROM THIS lOT OCCURS

(JMP DEVPIC
DEVINT
DEVAC

/RESTORE DEVINT IN
/CASE API DISABLED.
/RESTORE AC
/ION OR 10F
/DEBREAK AND RESTORE CONDITIONS
/OF LINK, EX.MODE AND MEM.PROT.

DEVOUT

Since the auto-index registers and EAE registers are not used by the standard I/o device
handlers, it is not necessary to save and restore them.
The Monitor routine (.SETUP) checks the skip chain for the instruction which matches
SKP lOT; if there is a match it places the address, DEVINT, in the appropriate transfer vector (INTn)
and places JMS* INTn in the corresponding API channel register. If a match cannot be found, lOPS
outputs the following error message,
• lOPS

XXXXXX

indicating that the skip lOT in the CAL calling sequence at location XXXXXX was not in the skip
chain.

7-3

Refer to the operating procedures of the System Generator for the method of incorporating
new handlers and associated skip chain entries into the Monitor.
7.1.2

API Software Level Handlers
(This section assumes complete fami I iarity with Chapter 9 of the PDP-9 User Handbook.)

7.1.2.1

Setting Up API Software Level Channel Registers - When the Monitor is loaded, the API

software-level channel registers (40 through 43) are initial ized to
.SCOM+ 12
.SCOM+13
.SCOM+14
.SCOM+15

JMS*
JMS*
JMS*
JMS*

/LEVEL 4
/LEVEL 5
/LEVEL 6
/LEVEL 7

where the .SCOM registers are at absolute locations 00112 through 00115 and contain the address of
an error routine.
Therefore, prior to requesting any interrupts at these software priority levels, the user must
modify the contents of the .SCOM registers so that they point to the entry point of the user's software
leve I hand lers.
Example:
.SCOM = 100
LAC
DAC*

(LV5INT
(.SCOM+13

LV5INT exists in the user's area in the following format:
LV5INT

0
DAC
SAV5AC
/SAVE AUTO INDEX REGISTERS
/IF LEVEL 5 ROUTINES
fUSE THEM AND LOWER LEVEL
/ROUTINES ALSO USE THEM
/SAVE MQ AND STEP COUNTER
/IF SYSTEM HAS EAE AND IT
/IS USED AT DIFFERENT LEVELS •

fpC, LINK, EX.MODE, MEM.PROT.
/SAVE AC

.
/RESTORE SAVED REGISTERS.
DBR
XCT
.+ 1
JMP*
LV5INT
7.1.2.2

/DEBREAK FROM LEVEL 5
/AND RESTORE L, EX.MODE, MEM.PROT.

Queueing - High priority/high data rate/short access routines cannot perform complex cal-

culations based on unusual conditions without holding off further data inputs. To perform the calculations, the high priority program segment must initiate a lower priority (interruptable) segment to perform

7-4

the calculations. Since, in general, many data handling routines will be requesting calculations, there
wi II exist a queue of calculation jobs waiting to be performed at the software level. Each data handling
routine must add its job request to the appropriate queue (taking care to raise the API priority level as
high as the highest level that manipulates the queue before adding the request) and issue an interrupt
request (ISA) at the corresponding software priority level. The general flow chart, Figure 7-1 depicts
the structure of a software level handler involved with queued requests.
LV5INT
SAVE PC,LlNK,AC,
AUTO-INDEX REGS,
MO, STEP COUNTER
AND CONDITIONS

OF E~TEND MODE
AND MEMORY PROTECT

Figure 7-1

Structure of API Software Level Handler

Care must be taken about which routines are called when a software level request is honored;
that is, if a caJ led routine is "open" {started but not completed} at a lower level, it must be reentrant
or errors will result.

NOTE
The standard hardware I/O device handlers do not contain reentrant procedures and must not be reentered from
higher software levels.
New resident handlers for Power Fail, Memory Parity,
nonexistent memory violation, and Memory Protect violation have been incorporated into the system and effect
an lOPS error message if the conditon is detected (see
Appendix E for lOPS errors). The user can, via a
.SETUP, tie his own handler to these skip lOT or API
channel resisters.

7-5

Standard API Channel/Priority Assignments

7.1 .3

Priority

Channel
Register

Software priority

DECtape

TC02

MAGtape

TC59

Drum

RM09

Disk

Paper Tape Reader

Clock overflow

Power fail

KP09

Parity

MP09

Display (L P flag)

34H

Card readers

CR01E
CR02B

2
2

Line Printer

647

A/D

138/139

DB99A/DB98A

DB09A

360 Data Li nk

Channel

Device

Option
Number

Channels 18 through 31 still unassigned.

7.2

WRITING SPECIAL I/o DEVICE HANDLERS
This section contains information prepared specifically to aid those users who plan to write

their own special I/o device handlers for the I/O or Keyboard Monitor systems. (Information on special
handlers for the Background/Foreground Monitor system will be available at a later date.) The PDP-9
Keyboard Monitor system is designed to enable users to incorporate their own device handlers; however,
precautions should be taken when writing the handler to ensure compatibility with the Monitor.
Special handlers cannot be incorporated into the I/O Monitor system, but can be designed
to run with user programs in the I/O Monitor environment (see Section 7.2.4). In an I/O Monitor system, if a user wishes to incorporate a special handler into a systems program (for example, a card punch
handler for MAC RO-9), he must purchase the source tape and assembly listings, modify them symbolically,
and reassemble using at least a 16K machine.

7-6

It is assumed that the user is familiar with Section 7.1 of this chapter. To summarize, the
handler is entered via a JMP from the Monitor as a result of a CAL instruction. The contents of the
AC contain the address of the CAL in bits 3 through 17.

Bit 0 contains the Link, bit 1 contains the

extend mode status, and bit 2 contains the memory protect status. The previous contents of the AC and
Link are lost.
To show the steps required in writing an I/o device handler, a complete handler (Example B)
was developed with the aid of a skeleton handler (Example A). This handler is a non-reentrant type
(discussed briefly at the beginning of this chapter) and uses the Debreak and Restore instruction (DBR)
to leave the handler at software priority level 4 (if API), and restore the status of the Link, extend
mode, and memory protect. Example A is referenced by part numbers to illustrate the development of
Example B, a finished Analog to Digital Converter (ADC) I/o Handler. The ADC handler shown in
Example B, was written for the Type AF01B Analog to Digital Converter, discussed on pages 4-26 and
4-27 of the PDP-9 User Handbook. This handler is used to read data from the ADC and store it in the
user's line buffer. The handler shown in Example B is for instructional purposes only; it has not been
thoroughly tested.
The reader, while looking at the skeleton of a specialized handler as shown in Example A,
should make the following decisions about his own handler. (The decisions made in this case are in
reference to developing the ADC handler):
a. Services that are required of the handler (flags, receiving or sending of data, etc.).
By looking at the ADC lOT's shown in Chapter 4 of the Users Handbook, it can be seen that there are
three lOT instructions to be implemented. These instructions are: Skip if Converter Flag Set; Select
and Convert; and Read Converter Buffer.
The only service the ADC handler performs is that of receiving data and storing it in user
specified areas. This handler will have a standard 256-word buffer.
b. Data Modes used (for example, lOPS ASCII, etc.). As there is only one format of input
from the Type ~FOl B ADC, mode specification is unnecessary in Example C.
c. Which I/O macros are needed for the handler's specific use, that is, .INIT, .CLOSE,
.READ, etc. These are fully described in Chapter 3 of this manual. For an ADC, the user would be
concerned with three of the macros •
• INIT would be used to set up the associated API channel register and the interrupt skip
lOT sequence in the Program Interrupt (PIC) skip chain. This is done by a CAL (N) as shown in Part III
of Example A, where (N) is the channel address. The standard device/API channel associations can be
found on Pages 12 and 13 of the Users Handbook •
• READ is used to transfer data from the ADC. When the • READ macro is issued, the
ADC handler will initiate reading of the specified number of data words and then return control to the
user. The analog input data received is in its raw form; it is up to the programmer to convert the data
to a usable format •
•WAIT detects the availability of the user's buffer area and ensures that the I/o transfer
is completed. It would be used to ensure a complete transfer before processing the requested data.

7-7

d. Implementation of the API or PIC interrupt service routine. Example A shows an API
or PIC interrupt service routine that handles interrupts, processes the data and initiates new data requests to fully satisfy the .READ macro request. Note that the routines in Example A will operate with
or without API. Example B used the routines exactly as they are shown in Example A.
During the actual writing of Example B, consideration was given to the implementation
of the I/O Macros in the new handler in one of the following ways:
1. Execute the function in a manner appropriate to the given device as discussed in
(c) •• INIT, .READ, .WAIT were implemented into the ADC handler (Example B) under
the subroutine names ADINIT, ADREAD, ADWAIT.
Wait for completion of previous I/O. (Example B shows the setting of the ADUND
switch in the ADREAD subroutine to indicate I/O underway.)

2. Ignore the function if meaningless to the device. See Example B (.FSTAT results in
JMP ADIGN2) in the dispatch table DSPCH. For ignored macros, the return address
must be incremented depending upon the argument string after the CAL. The number of
arguments for each macro is shown in Chapter 3.

Issue an error message in the case where it is not possible to perform the I/o function. (An example would be trying to execute an .ENTER on the paper tape reader.)
In Example B the handler jumps to DVERR6 which returns to the Monitor with a standard
error code in the AC.

After the handler has been written and assembled, users who have a mass storage device must
rebuild the Monitor system using the System Generator (SGEN), conveying to it the following information:
a.

Answer "yes" for, "Are any other device handlers present?"

Give the total number of additional handlers.

c•

Type hand ler names.

Type number of skip lOT's.

Type skip lOT's

Type skip chain, in the desired order of priority (usually with high speed devices first).

An example of System Generation is shown in the SGEN section of the Keyboard Monitor
Guide (DEC-9A-NGBA-D).
When the system has been generated on a mass storage device, the system program UPDATE
must be used to add the new handler to the library. At this time, the user is ready to use his specialized device handler in the PDP-9 system.
For the I/O Monitor (paper tape systems), the user must assemble the handler and spl ice it to
the lOPS Library Tape (Number 1). This procedure is described following Example B.

7.2.1

Discussion of Example A by Parts
Part 1

Stores CAL pointer and argument pointer; also picks up function code from
argument string.

Part 2

By getting proper function code in Part 1 and adding a JMP DSPCH, the CAL
function is dispatched to the proper routine.

7-8

7.2.2

Q..

t
o

Q..

Part 3

This is the .SETUP CAL used to set up the API channel register and PIC skip chains.
Section 7.1.3 of this manual shows the standard device/API associations.

Part 4

Shows the API and PIC handlers. It is suggested these be used as shown.

Part 5

This area reserved for processing interrupt and performing any additional I/O.

Part 6

Interrupt dismiss routine.

Part 7

Increments argument pointer in bypassing arguments of ignored macro CALis.

Example A, Skeleton Vo Device Handler

ISPECIALIZED 1/0 HANDLER
ICAL ENTRY ROUTINE
.GLOBL DEV.
• MED=3
DAC
DEV.
DVCALP
DAC
DVARGP
ISZ
DVARGP
DVARGP
LAC*
(77777
AND
DIJARGP
ISZ
TAD
(JMP DSPCH)
DAC
DSPCH
DSPCH
XX
JMP
DVI NIT
JMP
DVFSAT
DVSEEK
JMP
DVENTR
JMP
JMP
DVCLER
JMP
DVCLOS
JMP
DVI'IITAP
JMP
DVREAD
D'JI.~RTE
JMP
DVI~AIT
JMP
DVTRAN
JMP

IMUST BE OF FORM AAA •
I.MED (MONITOR ERROR DIAGNOSTIC)
ISAVE CAL POINTER
lAND ARGUMENT POINTER
IPOINTS TO FUNCTION CODE
IGET CODE
IREMOVE UNIT # IF APPLICABLE
IPOINTS TO CAL + 2
IDISPATCH WITH
IMODIFIED JUMP
II = IINIT
12 = .FSTAT, .DELET, .RENAM
13 = .SEEK
14 = .ENTER
15 - • CLEAR

= . CLOSE
= .MTAPE
110 = .READ
111 - .WRITE
112 = .WAIT
113 = .TRAN
/6

IILLEGAL FUNCTIONS IN ABOVE TABLE CODED AS:
JMP
DVERR6

IFUNCTION CODE ERROR
DVERR6
LAW 6
JMP*
( MED+ 1 )

IERROR CODE 6
ITO MONITOR

IDATA MODE ERROR
DVERR7
LAlli 7
JMP*

(.MED+1)

IERROR COD: 7
ITO MON ITOR

IDEVICE NOT READY
DVERR4
LAC

(RETlJRiiJ)

IRETURN (ADDRESS IN HANDLER)
ITO RETURN IS W~~N NOT READY
ICONDITION HAS BEEN REMOVED)

( • MED)

IERROR CODE 4
ITO MONITOR

(.MED+1 )

7-9

11/0 UNDERWAY LOOP
DBR
DVBUSY
JMP*

IBREAK FROM LEVEL 4
ILOOP ON CAL

DVCALP

INORMAL RETURN FROM CAL
DVCK
DBR
DVARGP
JMP*

IBREAK FROM LEVEL 4
IRETURN AFTER CAL AND
IARGUMENT STRING.

ITHE DVINIT ROUTINE MUST INCLUDE
IA. SETUP FOR
lEACH FLAG CONNECTED TO PIC (AT BUILD TIME)
lONE OF THESE MAY ALSO BE THE API SETUP CALL.
ITHE SETUP CALLING SEQUENCE IS:
DVINIT

CAL

IN = API CHANNEL REGISTER

1(40-77); 0 IF NOT

ICONNECTED TO API

IIOPS FUNCTION COvE
ISKIP lOT TO TEST THE FLAG
IADDRESS OF INTERRUPT
IHANDLER (API OR PIC)

16'

SKP lOT
DBVINT

ITHIS SPACE CAN BE USED FOR 1/0 SUBROUTINES
IINTERRUPT HANDLER FOR API OR PIC
DEVAC
DEVPIC
DAC
(0)
LAC*
DEVOUT
DAC
DEVION
LAC
DVSTON
JMP
DEVPIC
DEVINT
JMP
DEVAC
DAC
DEVINT
LI\C
DEVOUT
DAC
IORS
SMA!CLA
LAI"

DVSTON
DEVION
{

TAD
DAC
DEVCF
ION

IS,WE AC
ISACE PC, LINK, EX. MODE,
IMEM. PROT.
IFORCE ION AT DISMISSAL

IPIC ENTHY
IAPI ENTRY, SAVE AC
IS AVE PC, LINK, EX. MODE,
IMEM. PROT.
ICHECK STATUS OF PIC
IFOR RESTORATION AT
IDISMISSAL.

1 7740

DEVION
DVS1vCH

ICLEAR FLAG
IENABLE PIC

ITHIS IS THE AREA DEVOTED TO PROCESSING INTERRUPT AND
IPERFORMING ANY ADDITIONAL 1/0 DESIRED.
IOF
DEVIOT

IDISABLE PIC TC INSURE
IDISMISSAL BEFORE
IINTERRUPT FROM THIS
IIOT OCCURS

IINTERRUPT HANDLER DISMISS RTE
(JMP DEVPIC)
DVDISM
LAC
DEVINT
DAC
DEVAC
LAC
DVS\I/r:H
ION
DBR
DEVOUT
JMP*

IRESTORE PIC ENTRY
IRESTORE AC
lION OR lOr
IDEBREAK AND RESTORE
IlINK, EX. MODE, MEM. PROT.
7-10

IIF THE HANDLER USES THE AUTO-INDEX
lOR

IEAE REGISTERS, THEIR CONTENTS
ISHOULD BE
ISAVED AND RESTORED.
IFU~CTIONS POSSIBLY IGNORED SHOULD
ICONTAIN PROPER INDEXING TO BYPASS
IARGUMENT STRING.

~:( DVIGN2
~

7.2.3

ISZ
JMP

DVARGP
DVCK

/BYP~SS

tILE POINTER

Example a, Special I/o Handler for Type AFOla AID Converter

IADC lOT'S
ADSF=701301
ADSC=701304
ADRB=701312
IADSF=SKIP IF CONVERTER FLAG IS SET
IADSC=SELECT AND CONVERT(ADC FLAG IS CLE4RED
lAND A CONVERSION IS INITIALITED)
IADRB=READ CONVERTER BUFFER(PUTS CONTENTS IN !\ C)
ICAL ENTRY ROUTINE
IADC. IS GLOBAL NAME FOR HANDLER
.GLOBL ADC.
IMED(MONITOR ERROR DIAGNOSTIC)
.MED=3
ISAVE CAL POINTER
DAC ADCALP
ADC.
lAND ARGUMENT POI~TER
DAC 4DARGP
IPOINTS TO FUNCTION CODE
ISZ ADARGP
IGET CODE
LAC* ADARGP
IPOINTS TO CAL + 2
ISZ ADARGP
TAD (JMP DSPCH)
IDISPATCH WITH
DAC DSPCH
IMODIFIED JUMP
XX
OSPCH
JMP ADINIT
II = .INIT
JMP ADIGN2
12 = .FSTST, • DELET, • RENAM
JMP ADIGN2
13 = .SEEK
JMP ADFRR6
14 - .ENTER
~MP ADFRR6
15 = .CLEAR
JMP ADOK
16 = .CLOSE
JMP ADOK
17 = .MTAPE
JMP ADREAD
110 = .READ
JMP ADERR6
III = .WRITE
JMP ADWAIT
112 = .WAIT
JMP ADERR6
113 = .TRAN
IILLEGAL FUNCTIONS IN ABOVE TABLE CODED AS:
I
JMP ADERR6
IFUNCTION CODE ERROR
AOERR6
LAW 6
IERROR CODE 6
ITO MONITOR
JMP* (.MED+1)
IOATA MODE ERROR
AOERR7
LAW 7
IERROR CODE 7
JMP* (.MED+!)
ITO MONITOR

7-11

ITHE ADINT ROUTINE MUST INCLUDE A
I. SETUP FOR
lEACH FLAG ASSOCIATED WITH THE
IDEVICE
ITHE .SETUP CALLING SEQUENCE IS:
ADINIT
ISZ ADARGP
.DEC
LAC (256
.OCT
DAC* ADARGP
ISZ ADARGP
CAL 57

IIDX TO RET STNDRD BUFF SIZE

ISTANDARD BUFFER SIZE (DECI~AL)
IPUT BACK STANDARb BUFFER SIZE
157=API CAHNNEL RF-GISTER

1(40-77); 0 IF NOT

ICONNECTED TO API
I.SETUP lOPS FUNCTION CODE
ADSF
IADC SKIP lOT TEST THE FLAG
ADCINT
IADDRESS OF INTERRUPT
IHANDLER (API OR PIC)
ADUND
LAC .+2
IERASES CALL FU~CTION IN CASE
ADI,IRC
DAC .-5
10F FURTHER .INIT'S THEY WILL BE
ADWPCT
JMP ADS TOP
IIGNORED By THIS JMP TO ADSTOP
IWHERE THE 1/0 UNDERWAY SWITCH
lIS CLEARED AND ALL 1/0 IS
ITERMINATED
ITHE PREVIOUS SIX TAGS IN THE CAL AREA ARE USED FOR TEMP
ISTORAGE DURING THE ACTUAL .READ FUNCTION
IADCKSM IS FOR STORING THE CHECKSUM
IADDRP IS THE CURRENT BUFFER POINTER
IADLRHP IS THE LINE BUFFER HEADER POINTER
IADUND IS FOR DEVICE UNDERWAY SWITCH
IADRWC IS USED AS A -WORD COUNT REGISTER
IADRWCT IS USED TO STORE CURRENT WORD PAIR COUNT
ISTOP ADC ROUTINE CLEARS 1/0 UNDER WAY SWITCH
ADSTOP DZM ADUND
IADC WAIT LAC ADUND
SNA
JMP ADaK
11/0 UNDERWAY LOOP
ADBUSY
DBR
JMP* ADCALP
ADCKSM
ADCBP
ADLBHP

ADREAD

LAC ADUND
SZA!CMA
JMP ADBUSY
DAC ADUND
LAC* ADARGP
DAC ADDBP
DAC ADLBHP
ISZ ADARGP
LAC* ADRAGP
DAC ADRWC
ISZ ADARGP
DZM ADWPCT
DZM ADCKSM
ISZ ADDBP
ISZ ADDBP

ICHECK TO SEE IF 1/0 IS UNDERWAY
IIF NOT SET IT WITH -1
lIT WAS SET, GO BACK TO CAL
ISET IT
IGET LI~E BUFFER HEADER POINTER
ISTORE IT
IALSO STORE IT FOR LATER HEADER
IINCREMENT ARG. POINTER
IGET -L~B.W.C.(2'S CaMP)
ISTORE IT IN WORD COUNT REGISTER
IINCREMENT FOR EXIT FROM .READ
IZERO WORD PAIR COUNT REG.
IZERO CHECKSUM REG.
IGET PAST HEADER PAIR
INOW POINTING AT BEGINNING OF
IBUFFER
1ST ART UP DEVICE

ADSC
INORMAL RETURN FROM CAL
ADOK
DBR
JMP* ADARGP

IBREAK FROM LEVEL 4
IRETRUN AFTER CAL
7-12

IINTERRUPT HANDLER FOR API OR PIC
ADCPIC
DAC ADCAC
LAC* (0)
DAC ADCOUT
LAC ADCION
JMP ADSTON
ADCINT
JMP ADCPIC
DAC ADCAC
LAC ADCINT
DAC ADCOUT
LAC (JMP ADAPIC)
DAC ADCINT
IORS
SMA!CLA
LAW 11140
TAD ADCION
ADSTON
DAC ADSWCH
ADRB
ADCION
ION
DAC* ADDBP
ISZ ADDBP
ISZ ADWPCT
TAD ADCKSM
DAC ADCKSM
ISZ ADRWC
JMP ADCONT
LAC ADWPCT
TAD <1
RTL
RTL
RTL
RTL
AND (311000
DAC* ADLBHP
IS~ ADLBHP
TAD ADCKSM
DAC* ADLBHP
DZM ADUND
JMP ADDISM
IOF
ADCONT
ADSC

ISAVE AC
ISAVE PC, LINK, EX. MODE
IMEM. PROT.
IFORCE ION AT DISMISSAL
IPIC ENTRY.
IAPI ENTRY, SAVE AC
ISAVE PC,LINK,EX. MODE,
IMEM. PROT.
IRESTORE PIC ENTRY BECAUSE PIC
IA JMS CALL NOT A JUMP
ICHECK STATUS OF PIC
IFOR RESTORATION AT
IDISMISSAL
IREAD CONVERTER BUFFER
IENABLE PIC FOR OTHER DEVICES
ISTORE DATA IN USER BUFFER
IINC. BUFFER POINTER
IINC. WORD PAIR COUNTER
IADD CHECKSUM
ISTORE IT
lIS 1/0 COMPLETE
INO KEEP GOING
IYES,COMPUTE WORD COUNT PAIR
IADD ONE MAY BE ODD
IDIVIDE By TWO, AT SAME TIME ADS
IIT,FOR HEADER
IALL SET
ISTOHE IN HEADER #1
IINC. TO STORE CKSUM
IADD WORD PAIR COUNT
ISTORE IN HEADER #2
ICLEAR DEVICE UNDERWAY
IEXIT
IDISABLE PIC TO INSURE
IDISMISSAL BEFORE
IINTERRUPT FROM THIS
IIOT OCCURS

IINTERRUPT HANDLER DISMISS RTE
ADDISM
LAC ADCAC
ADSWCH
ION
DBR
JMP* ADCOUT
ADCAIP
0
~DARGP
0
ADCOUT
PJ
ADCAC
0

IRESTORE AC
lION OR IOF
IDE9REAK AND RESTORE
ILINK,EX.MODE,MEM. PROT.
IADC CAL POINTER
IADC ARGUEMENT POINTER
IPC,L,FM,MP
lAC SAVED HERE

IIF THE HANDLER USES THE AUTO-INDEX
lOR
IEAE REGISTERS, THEIR CONTENTS
ISHOULD BE
ISAVED AND RESTORE.
7-13

/FUNCTIONS POSSIBLY IGNORED SHOULD
/CONTAIN PROPER INDEXING TO BYPASS
/ARGUMENT STRING.
ADIGN2
ISZ ADARGP
JMP ADO'X
.END
7.2.4

/BYPASS FILE POINTER

Incorporating Special, User-Program I/O Handler into Paper Tape System
Proceed as follows to incorporate a nonstandard device handler into a user program in the

I/O Monitor environment.
a. Assemble the new. handler in relocatable binary form. After removing the end-of-file
block {with the W switch in PIP}, attach it to the I/O tape {No.1} of the library.
b.

Write a main program in which the new handler is declared as an external global:
.GLOBL

NUHDLR

Perform the following sequence of instructions prior to the execution of any monitor
calls to the .DAT slot(s} to which this handler is to be attached:
LAC
DAC*
DAC*

NUHDLR
(140

/.OAT SLOT *3
/.DAT SLOT *4

{141

Do not put these • DAT slot numbers in a .IODEV psuedo-op.

On the first .INIT to this handler, the handler should:
1. Place the skip lOT in the skip chain in place of an unused skip lOT (avoid DRNEF)
PAPER TAPE SYSTEM SKIP CHAIN
LOC

SKP lOT

1511
1514
1517
1522
1525
1530
1533
1536
1541
1544
1547
1552
1555
1560
1563

SPFAL
DRSF
MTSF
CLSF
RCSF
RCSD
LSDF
RSF
PSF
KSF
TSF
MPSNE
MPSK
SPE
DRNEF

DEVICE
POWER FAIL
DRUM DONE
MAGTAPE DONE
CLOCK OVERFLOW
CARD COLUMN READY
CARD DONE
LINE PRINTER DONE
PAPER TAPE READER DONE
PAPER TAPE PUNCH DONE
KEYBOARD READY
TELEPRINTER DONE
NON-EXISTENT MEMORY
MEMORY PROTECT VIOLATION
MEMORY PARITY ERROR
NOT DRUM ERROR

An example is:

LAC
DAC*

(skip lOT)
(IE33)

7-14

/REPLACE LINE
/PRINTER SKIP lOT

Call .SETUP

CAL
16
SKIP lOT
DEVINT

IADDRESS OF API REGISTER
SETUP FUNCTION CODE

I ADDRESS OF INTERRUPT SERVICE

Where AD is the address of the associated API channel register; it is 0 if this device
is not attached to the API.
e.

The setup for communication with this nonstandard handler via .DAT slots 3 and 4 is

complete.
NOTE
This procedure refers to the current Paper Tape System
being distributed where .DAT slot Number 1 is at absolute register 136j:l' A more modular verision is to be
distributed in the tUture.

7.3

1/0 HANDLERS ACCEPTABLE TO SYSTEM PROGRAMS
This section lists the .DAT slot requirements of system programs, the uses made of the .DAT

slots, and the I/O handlers that may be assigned to each. It is imperative that one and only one I/o
handler for a device be in core at the same time; that is, DTA. and DTB. should not be brought in together since there is no communication between the two interrupt handlers.

IFORTRAN IV

.DAT Slot

Use

-11

Input

Handler

TTA
PRA
PRB (recommended)
DTA, DKA, ORA, or MTA
(required if 3 files open)
DTB, DKB, ORB, or MTB
(recommended if 2 files open)
DTC, DKC, DRC, or MTC
(recommended if input only)
DTD, DKD, ORO, or MTD
MTF (non-file-oriented)
CDA
COB
CDC

-12

Listing

TTA
LPA
PPA
DTA, DKA, ORA, or MTA
(required if 3 files open)

7-15

.DAT Slot

Use

Handler
DTB, DKB, DRB, or MTB
{recommended if 2 files open}
DTD, DKD, DRD, or MTD
{recommended if listing output only}
MTF {non-fi le-ori ented}

-13

Output

PPA
PPB
PPC {recommended}
DTA, DKA, DRA, or MTA
(required if 3 fi les open)
DTB, DKB, DRB, or MTB
{recommended if 2 files open}
DTD, DKD, DRD, or MTD
(recommended if listing output only)
MTF (non-file-oriented)

IMACRO-9

Identical to FORTRAN IV, with two exceptions (a) if .ABS binary output is requested on
.DATslot-13, PPC. and DTB. cannot be used.

(b) .DATslot-10 is the secondary input device (P

option in command string) and should be attached to a non-bulk-storage handler:

TTA
PRA
PRB
CDA
CDB
CDC

IEDIT-9
.DAT Slot

Use

-10

Secondary
Input

Handler

TTA
PRA
PRB (recommended)
CDA
CDB
CDC

7-16

.DAT Slot
-14

Use
Input

Handler

TTA
PRA
PRB (recommended)
DTA, DKA, ORA, or MTA
(required if input and output)

DTD, DKD, ORO, or MTD
(input only)

CDA
COB
CDC
-15

Output

LPA
TTA
PPA
DT A, DKA, ORA, or MTA
(required if input and output)

DTD, DKD, ORO, or MTD
(output only)

Linking Loader
and DDT

.DAT Slot
-1

Use
System
Library

Handler

PRA
DTA, DKA, or MTA
DTB, DKB, or MTB
DTC, DKC, or MTC
(recommended if no user I/O)

DTD, DKD, or MTD
CDA
COB
CDC
-4

Input

Same as for . OAT slot -1 plus
ORA

-5

External User
Library

ORB
DRC
ORO

NOTE
Since Linking Loader handlers can be used by the user
program, choice of the bulk-storage handler should be
a function of user requirements.

7-17

PIP uses all the positive . OAT slots (1 through 10) plus . OAT slot -3 for Teletype I/O.
Prior to PIP use, any non-standard peripheral device assignments should be made via the
ASSIGN command to the PDP-9 Keyboard or Background/Foreground Monitor. If several PIP functions are to be used with a variety of peripherals, assignment of all these peripherals to Device Assignment Table (OAT) slots (1 through 10) will avoid returning to the Monitor for reassignment of OAT slots
and reloading PIP and its new lOPS routines into memory. The following should be carefully noted in
using the ASSIGN command to set up OAT slots for PIP. Since the PDP-9 ADVANCED Software System
includes more than one device handler for certain peripherals, those used with PIP should normally be
the ones with the fullest capabilities, for example, PRA, PPA and DTA. If both input and output are
to occur to the same type device (for example, DECtape), separate slots must be assigned. Both, however, must be assigned to the same handler, that is, erroneous results will occur if DT A is assigned to
one slot and DTB to another, since there is no communication between the interrupt service routines.
The user must be certain to clear (ASSIGN NONE A, B, C,J , where A, B, and C are the OAT slots
to be cleared), undesirable assignments.

ISystem Generator
• OAT Slot

Use

Handler

-14, -10

Input

DTA, DKA, or MTA

-15

Output

DTA, DKA, or MTA
PTD, DKD, or MTD

IDUMP
-12

listing

LPA
TTA
PPA

-14

Input

OTA, DKA, ORA, or MTA
DTD, DKD, ORO, or MTD
(recommended)

7-18

17-TO-9 CONVERTER I
Handler

.OAT Slot

Use

-12

Listing

TTA
LPA
PPA
OTA, OKA, ORA, or MTA
(required if 3 files open)
OTB, OKB, ORB, or MTB
(recommended if 2 files open)
OTO, OKO, ORO, or MTO
(recommended if 1 file open)

-14

Input

TTA
PRA
PRB (recommended)
OTA, OKA, ORA, or MTA
(required if 3 files open)
OTB, OKB, ORB or MTB
(recommended if 2 fi les open)
OTC, OKC, ORC, or MTC
(recommended if input only)
OTO, OKO, ORO, or MTO
COA
COB
CDC

-15

Output

LPA
TTA
PPA
OTA, OKA, ORA, or MTA
(required if 3 files open)
OTB, OKB, ORB, or MTB
(recommended if 2 files open)
OTO, OKO, ORO, or MTO
(recommended if output only)

I Libary Update I
-10

Secondary
Input

PRA
OTA, OKA, ORA, or MTA
COA

-12

Listing

LPA
TTA
PPA
OTA, OKA, ORA, or MTA
COA

7-19

.DAT Slot

Use

Handler

-14

Input

PRA
DTA, DKA, ORA, or MTA

-15

Output

PPA
PPB
PPC
DTA, DKA, ORA, or MTA
NOTE

The A version of bulk-storage handlers (DTA, DKA,
etc.) can handle only three files simultaneously; any
one of them should never be assigned to all four
Library Update • OAT slots.

ISystem Patch
.DAT Slot

Use

-14

System Device
I/O

DTA, DKA, MTA
DTD, DKD, MTD

-10

Secondary
Input

PRA

Handler

NOTE
PATCH uses • OAT slot -3 for teletype output and
• OAT slot -2 for input from the keyboard of batch
input device. The user should never modify .DAT
slots -3 or -2.

I Chain Bui Ider I
.DAT Slot

Use

-6

Output

7-20

Handler

PPA
PPB
PPC
DTA, DKA, ORA, or MTA
DTB, DKB, ORB, or MTB
(recommended)
DTD, DKD, ORO, or MTD
(only if no other DT, OK, etc.,
in -4, -5, and -1)

Handler

.DAT Slot

-5

External
Library

-4

User Programs

-1

System Library

PRA
CDA
DTA, DKA, ORA, or MTA
DTB, DKB, ORB, or MTB
(recommended)
DTC, DKC, DRC, or MTC
(only if no other DT, OK, etc. in -6)
DTD, DKD, DKD, or MTD
(only if no other DT, OK, etc. in -6)
(Same as for • OAT -5)

NOTE
Use smallest handlers possible since they are not recoverable as user handlers.

I Chain Execute

-4

Chain Input

PRA
CDA
DTA, DKA, ORA, or MTA
DTB, DKB, ORB, or MTB
DTC, DKC, DRC, or MTC
DTD, DKD, ORO, or MTD

NOTE
Use smallest "input-only" handler since user program
may not use this handler.

7.4

SUMMARY OF STANDARD I/O HANDLER FEATURES
This section applies to I/O and Keyboard Monitor environments only.

ILPA.(647 LINE PRINTER)
A.

Function

.INIT

(a) Return standard line buffer size (52 10)
(b)

.SETUP --- API channel register 56 8

7-21

.DLETE
.RENAM
• FSTAT

Ignore

.SEEK

Illegal function

.ENTER

Ignore

.CLEAR

Ignore

.CLOSE

(a) Allow previous output to terminate

(b) Form feed
(c) Allow form feed to terminate

.MTAPE

Ignore

10.

.READ

Illegal function

1l.

.WRITE

(a) Allow previous output to terminate
(b)

12.

•WAIT

Allow previous output to terminate

13.

.TRAN

Illegal function

Lega I Data Modes

l.
C.

Output line

lOPS ASCII

Vertical Control Characters (when first character of line)

12
21

Pri nt every line

Print every third line

Print every sixth line

Print every tenth line

Print every twentieth line

Overprint

Form feed

Print every second line

Horizontal Control Characters (anywhere in line)

Horizontal tab -- converted to N spaces, where N is the
number necessary to have the next character in column

11,21,31,41, •.•
E.

Recoverable Errors
1.

Device not
ready

Monitor error message, .IOPS 4. Make device ready, then
type tR to continue.

7-22

Unrecoverable Errors
1.

Illegal function

Illegal data
mode

Monitor error message, • lOPS 06 XXXXXX, where XXXXXX
is address of error CAL.
(a)

.SEEK

(b)

.READ

(c)

• TRAN

Monitor error message, .IOPS 07 XXXXXX, where XXXXXX
is address of error CAL.
Any mode other than lOPS ASCII.

Program Size
297 (decimaO registers.

ITT A- (TELETYPE) I
A.

Functions - All function descriptions (except READ and WRITE) refer to action taken when either
the teleprinter or the keyboard is addressed.
1.

.INIT

(a) Return standard buffer size (34 10).
(b) Assign return addresses for certain control characters from
contents of CAL ADDRESS + 2. Bits 0 through 1 in CAL + 2
address are set to designate caller:

BO, 1 = 01
BO,1=10
BO, 1 = 00

caller = KM9
caller = DDT
caller = any other user

.DLETE
.RENAM
• FSTAT

Ignore

.SEEK

Ignore

.ENTER

Ignore

.CLEAR

Ignore

.CLOSE

(a) Set VA UNDERWAY indicator.
(b) Print CR/LF.

.MTAPE

10.

.READ

ve.

Ignore
(a) Set VA UNDERWAY indicator.
(b) Set up to accept characters from keyboard.

7-23

11.

.WRITE

(a) Set VO UNDERWAY indicator.
(b)

B•

Print line.

12.

•WAIT

Allow input or output to finish •

13.

•TRAN

Illegal function •

Lega I Data Modes

lOPS ASCII

IMAGE ASCII

Vertical Carriage Control Characters
1.

Output

(a) Line feed (12a)

(1) lOPS ASCII: Ignore all leading line feeds; otherwise
output
(2) IMAGE: Output
(b) Others (vertical tab, form feed) output
2.
D.

Inserted in buffer

Input

Horizontal Carriage Control Characters
Tab (l1a) in or out
1.

lOPS ASCII

(a) Model 33 - output sufficient number of spaces to place the
next typed character in column 11, •.• , 71 .
Insert only 11a in buffer on input.
(b) Model 35 - input, insert 11 R in buffer. Output, print tab.

2.
E.

IMAGE

Input, insert 11a in buffer. Output, print tab.

Program Control Characters-IN
1•

Stop current Vo
to Teletype.

Decode character (a) tC transfers control to the address specified as return in
the • IN IT performed by KM9.
and echo on Te leprinter. *
(b) tP transfers control to the address specified as return in
the .INIT performed by the user (other than KM9 or DDT).
(c)

tT transfers control to the address specified as return in the
.INIT performed by DDT.

(d)

fS transfers control to the address specified in .SCOM + 6.

(e)

fQ transfers control to KM9SAV.

*Character will be ignored {not echoed} in cases (a), (b), and (c), if respective •• INIT has not been
performed.

7-24

Data Control Characters-IN
1.

IMAGE Mode

All characters inserted in buffer as 7-bit characters.

lOPS ASCII
Mode

(a)

Rubout. Delete previous character typed. Type out reverse
slash (\).

(b)

tU delete entire line typed so far. Type out commercial
at (@). If output is UNDERWAY, printing is terminated
and a CR/LF is output.

G. Data Control Characters-OUT (both modes)
Ignore rubout (177 8 ) and null (00).
In image alpha mode, a rubout should be used to fill the last word pair when an odd
number of characters is to be output.
H.

Errors (no program-initiated recovery)
1•

IIlega I data mode

Error code 7

Illegal function

Error code 6

Program Size
469 10 registers (this is included in resident MONITOR).

Teletype I/o - Can be requested only from mainstream in API systems, since the Teletype is not
connected to the API.

Ipp (PAPER TAPE PUNCH) I
A.

Functions

.INIT

(a)

Return standard buffer size (52 10),

(b)

.SETUP - no API.

(c)

Punch two fanfolds of leader.

.DLETE
.RENAM
.FSTAT

Ignore

• SEEK

Illegal function •

.ENTER

Ignore

.CLEAR

Ignore

7-25

.CLOSE

(a) Allow previous output to terminate.
(b)

Punch EOF if lOPS Binary

.MTAPE

Ignore

10.

• READ

Illegal function

11.

.WRITE

(a) Allow previous output to terminate.
(b) Output buffer

12.

•WAIT

Allow previous output to terminate •

13.

.TRAN

Illegal function

Lega I Data Modes
1.

lOPS Binary

IMAGE Binary

lOPS ASCII

IMAGE ASCII

Dump

C. Vertical Control Characters (lOPS ASCII only)
May appear only as first character of line, if elsewhere in line will be ignored; if no vertical
control character at beginning of line, a line feed (012) will be used.

012

Line feed

013

Vertical tab, followed by four deletes (177)

014

Form feed, followed by 408 nulls (000)

Horizontal Control Characters (lOPS ASCII only)
1.

011

Horizontal tab, followed by one delete (177)

Recoverable Errors
1.

No tape in punch

Monitor error code 4
(a) Put tape in punch
(b) Type tR

7-26

Unrecoverable Errors
1.

Illegal function

Illegal data mode

Monitor error code 6
(a)

.SEEK

(b)

.READ

(c)

• TRAN

Monitor error code 7

Program Size

PPA. (all data modes)
PPB. (a II except lOPS ASCII)
PPC. (lOPS binary only)

In API systems, the paper tape punch can be called only from mainstream, since the punch is not

397 decimal registers
270 decimal registers
210 decimal registers

connected to the AP I.

I
A.

PR (PAPER TAPE READER)

Functions

. IN IT

(a)

Return standard line buffer size (52 10)

(b)

.SETUP API channel register 50S

(c)

Clear I/O UNDERWAY indicator

• DLETE
.RENAM
.FSTAT

Ignore

.SEEK

Ignore

.ENTER

Illegal function (error code 6)

.CLEAR

Illegal function (error code 6)

.CLOSE

Allow previous input to finish and then clear I/O UNDERWAY
indicator •

• MTAPE

Ignore

10.

.READ

(a)

Allow previous input to be completed.

(b) Input line or block of data (see modes below).
11.

.WRITE

Illegal function (error code 6).

12.

• WAIT

Allow previous input to be completed before allowing user
program to continue •

13.

• TRAN

Illegal function.

7-27

B•

Lega I Data Modes (A 11 )
1.

lOPS ASCII

(a) Constructs line buffer header, computing:
(1) Word pair count
(2) Data mode
(3) Data validity bits
(b)

Packs characters into the line buffer in 5/7 ASCII, checking
parity (eighth bit, even) on each character.

(c) Allows vertical form control characters. (FF, LF, VT) only in
character position 1 of the I ine buffer. Otherwise, ignored.
(d) Terminates reading on CR or line buffer overflow. In the latter
case, tape is moved past the next CR to be encountered.
2.

lOPS BINARY

(a)

Reads binary data in alphanumeric mode, checking parity
(seventh hole, odd) on each frame.

(b) Accepts line buffer header at head of input data, modifying
data validity bits if parity or checksum errors (or short line)
have occurred.

(c) Terminates reading on overflow of word pair count in line
buffer header or word count in .READ macro, whichever is
smaller, moving tape to end of line or block if necessary.
3.

IMAGE ASCII

(a) Constructs line buffer header, computing:
(1) Word pair count
(2) Data mode
(b) Stores characters, without editing, or parity checking in the
I ine buffer, one per register.
(c) Terminates reading as a function of .READ macro word count.

IMAGE BINARY

Same as 3 (a), (b), (c) above; however, a binary read is issued to
the PTR.

DUMP

Same as 3 (b), (c) above. A binary read is issued to the PTR. No
header is constructed; loading begins at the core address specified
in the .READ macro.

NOTE
An end of tape condition causes the PTR interrupt service
routine to terminate the input line, turning off the I/O
UNDERWAY program indicator and marking the header
(data mode bits) as an EOM (end of medium) for all modes
except DUMP.

7-28

Unrecoverable Errors

2.
I.

Illegal Function

Monitor error code 6
(a)

.ENTER

(b)

.CLEAR

(c)

.WRITE

(d)

.TRAN

I II ega I Data Mode Monitor error code 7

Program Size
PRA. (all data modes)
PRB. (lOPS ASCII only)

436 decimal registers
287 decimal registers

IDT (DECT APE)
A.

Function
1.

.INIT

(a)

Return standard line buffer size (255 10)

(b)

.SETUP - API channel register 448

(c) Set direction switch (input or output).
NOTE
In order to change transfer direction when operating in
a file oriented environment, a new .INIT must first be
executed.
2.

.OPER (.DLETE)
(.RENAM)
(.FSTAT)
(a)

• DLETE
(1)

Examines specified Directory for presence of desired
fi Ie name. If not found, AC = 0 upon return to user.

(2)

Deletes file name (clears to 0) from the Directory of the
specified unit.

(3) Clears file bit map corresponding to deleted entry.
(4) Clears corresponding occupancy bits in Directory bit map.
(5)

Records modified Directory and file bit map b lock on
specified unit.

7-29

(b)

.RENAM
(1)

Examines specified Directory for presence of desired
file name. If not found, AC = 0 upon return to user.

(2) Changes file name in Directory to new one specified
by user program (no change is made to first block pointers).
(3)
(c)

Records modified Directory on specified unit.

• FSTAT
(1) Examines specified Directory for presence of desired
fi Ie name. If not found, AC = 0 upon return to user.
If found, AC = first block number of file. Also, bits
0- 2 of CAL ADDRESS + 2 = 1 = DECtape Directory type.

(d) Other .OPER codes are illegal.
3.

.SEEK

(a)

Loads into core the Directory of the unit specified if the
Directory is not already in core.

(b) Checks for presence of named file. (Error return to Monitor
if not found.)

.ENTER

(c)

Begins transfer of first block of file into handler buffer area,
overlaying Directory Entry Section but not Directory Bit Map.

(d)

Declares unit to be file oriented.

(a)

Loads into core the Directory of the unit specified if the
Directory is not already in core.

(b) Checks for presence of named fi Ie. If present, po inter to that
entry is saved for update at .CLOSE time. If not present,
empty slot is found for file name insertion at .CLOSE time.

(c) Examine Directory Bit Map for free block and saves that
block number for first transfer out and for insertion in
Directory Entry Section at .CLOSE time.
(d)
5.

.CLEAR

(a) Zero's out Fi Ie Bit Map blocks 71 through 77 on specified
DECtape unit.
(b)

Dec lares unit to be fi Ie oriented.

Initializes DECtape Directory block 100 to indicate that eight
blocks (71 through 100) are occupied.

(a) On input, clears internal program switches. On output, writes
2-cell EOF line as last line in output buffer (lOPS ASCII and
binary only) and outputs last data buffer with the data link
= 777777.
(b)

Loads into core the file bit map corresponding to the Directory
Entry in order to clear the Directory Bit Map of bits for blocks
formerly occupied by this fi Ie.

7-30

Loads Directory into memory, enters new entry and records
Directory again with new entry and updated Directory Bit
Map.

(e) Clears internal program switches.
7.

MTAPE (REWIND)
(BACKSPACE)

(a) REWIND
(1) Sets internal switches such that data transfer will begin

at block 0 in the forward direction.
(2) Declares the unit as non-file-oriented, that is, data will
be recorded (starting at block 0) every fifth block. At
EOT, recording continues in the reverse direction, etc.
Five passes will record all 1100a blocks of a DECtape.

(b) BACKSPACE
(1)

Decrements the internal pointer to the next block to be
transferred.

10.

.READ

(a) Input line from DECtape handler buffer or block of data to
user area. (See B be low for data modes.)
(b) Initiate input of next DECtape block when preceding block
has been emptied.

11.

•WRITE

(a) Transfers line or block of data from user area to DECtape
handler buffer.
(b) Outputs buffer when full, examining Directory Bit Map for
free block number to store as Data Link (word 377a) of current
block output.

12.

•WAIT

13.· •TRAN

B•

Allow previous transfer to be completed before allowing user
program to continue.
Transfer (in or out) the number of words specified by the user's
word count to/from the core area indicated in the. TRAN macro
to/from the specific block(s) desired by the user. Data will be
transferred to/from contiguous DECtape blocks in the forward
or reverse direction (also declared by the user). On input,
transfer stops on word count overflow. On output, transfer also
stops on word count overflow; however, if the word count is not
equivalent to an integral number of DECtape blocks, the remainder of the last block wi II be filled with zeros.

Lega I Data Modes
1.

lOPS ASCII

lOPS Binary

Image Alphanumeric

7-31

Image Binary

Dump

Recoverable Errors
1.

Monitor Error Code 4

Se lect Error*

(a) Ready the desired DECtape unit

(b) Type tR on the Teletype.
D.

Unrecoverable Errors
1.

Monitor Error Code 6

Illegal Function

(a) See E below for illegal functions
2.

Monitor Error Code 7

Illegal Data Mode
(a)

.SEEK with .INIT for output

(b)

.ENTER with .INIT for input.

Fi Ie Sti II Active

Monitor Error Code 10
(a)

Monitor Error Code 11

.SEEK, .ENTER
Not Executed
(a)

.SEEK, .ENTER, .CLEAR or .OPER when last file has not
been closed.

DECtape Error

.READ or .WRITE executed prior to .SEEK or .ENTER (or
.MTAPE - REWIND)
Monitor Error Code 12

(a) Mark Track Error
(b)
6.

Fi Ie Not Found

EaT during read or write
Monitor Error Code 13

(a) File name not found in Directory on a .SEEK.

Monitor Error Code 14
DECtape Directory
Full
(a) Directory Entry Section found full on an .ENTER.

DECtape Full

Monitor Error Code 15
(a) All DECtape blocks occupied on a •WRITE

Output Buffer
Overflow

Monitor Error Code 16
(a) Output line (lOPS ASCII or Binary) greater than 255 10 cells
(including header).

*A "Select" error is equivalent to a hardware not ready condition. See the PDP-9 Users Handbook,
F95, 5-12, for a detailed description.

7-32

(b)
10.

11.

12.

Monitor Error Code 17

Excessive Number
of Files Referenced
Two output files
on same unit
Illegal word pair
count tyVPC)

Output block (Image Binary or Image Alphanumeric) greater
than 255 10 cells (excluding header).

See Section E for file reference limitations.
Monitor Error Code 22
(a) Two output files open simultaneously on the same unit.
Monitor Error Code 23
(a) WPC = 0, or greater than 177.

Subprogram Description and Size
1.

DTA (which requires 2321 10 locations)
DTA is the most general DECtape handler issued with the PDP-9 ADVANCED Software
System. DTA has a simultaneous 3-file capacity, either input or output. Files may be
referenced on the same or different DECtape un its, except that two or more output fi les
may not be on the same unit. All data modes are handled as well as all lOPS functions
except .MTAPE. Three 256 10-word data buffers, three 32 10-word Directory Bit Maps
and three 32 10-word File Bit Maps are included in the body of the handler.

DTB (which requires 1552 10 locations)
DTB has a simultaneous 2-file capacity, either input or output. Both files may be on
the same or different units. DTB transfers data only in lOPS ASCII or lOPS binary data
modes. Included in the handler is space for two 256 10-word data buffers, two 32 10word Directory Bit Maps and two 32 10-word File Bit Maps. Functions included are:
.INIT
.SEEK

.ENTER
.CLOSE

.READ
.WRITE

.WAIT

DTC (which requires 680 10 locations)
DTC is the most limited (and conservative in terms of core allocation) DECtape handler
in the PDP-9 ADVANCED Software System. DTC is a READ ONLY handler with a 1-file
capacity requiring no space for bit maps and only one 256 10-word DECtape data buffer
to handle either lOPS ASCII or lOPS binary input (and no other). Functions included
are:
.INIT
.SEEK

.CLOSE
.READ

7-33

.WAIT

DTD (which requires 1569 10 locations)
DTD has full lOPS function capabilities including .MTAPE commands; however, it
allows for one and only one file reference, either input or output, at any given time.
Sequential fi Ie references are permitted. All data modes are acceptable to DTD.

One

256 10-word data buffer, one 32 10-word Directory Bit Map and one 32 10-word File Bit
Map are included.

ICD (Card Readers CROl E and CR02B) I
A.

Functions
l.

(a)

Return standard buffer size (52 10 )

(b)

Call .SETUP to update skip chain with PIC servicer addresses
for column ready and card done flags and to place API servicer
address in location 55 S (API channel 13).

.DLETE
.RENAM
.FSTAT

Ignored

.SEEK

Ignored

.ENTER

Illegal function

.CLEAR

Illegal function

• CLOSE

Allow previously requested input to terminate .

.MTAPE

Ignored

10.

.READ

.INIT

(a)

Allow previously requested input to terminate.

(b)

Ensure that device is ready.

(c)

Initiate input of next card.

1l.

.WRITE

Illegal function

12 .

• WAIT

Allow previously requested input to terminate.

13 .

• TRAN

Illegal function

LEGAL Data Modes
1.

Alphanumeric Input Modes
a.

lOPS ASCII (Mode 2) (36 10 locations required to store an SO-column card)
Eighty card columns are read and interpreted as Hollerith (029) data, mapped into

the corresponding 64-graphic subset of ASCII, and stored in the user's line buffer in 5/7
format. Compression of internal blanks to tabs and truncation of trailing blanks is not

7-34

performed; all SO characters appearing on the card are delivered to the caller's line
buffer. In addition, a carriage return (015 S) character is appended to the input line;
a total of Sl ASCII characters are thus returned by the handler in lOPS ASCII mode.
All illegal punch configurations (that is, those not appearing in the 029 Hollerith
set) are represented in the user's line buffer area as null (OO) characters. In addition,
the parity error bit is set in the line buffer header to indicate the illegal punch condition.
There is no possibility of confusion between those nulls representing illegal punch.
combinations and nulls to pad a word-pair containing fewer than five characters. The
reason for this lies in the fact that padding nulls are used only in the last pair of the
line, and these are always (in lOPS ASCII mode) preceded by a carriage return. Thus
any nulls which appear before the handler-supplied carriage return must be considered
to represent i lIega I punches.
The single addition to the Hollerith set, one made necessary by the constraints of
system programs, is the provision for the internal generation of the ALT MODE terminator.
The appearance of a 12-1-S punch (multiple-punched A/S) on the card is mapped into
the standard PDP-9 ALT MODE character (175 S) in the user's line.
When card processing is complete, word 1 of the header is constructed and stored
in the caller's line buffer area. Word 2 of the header, the checksum location, is never
disturbed by the card reader handler in lOPS ASCII mode.
Attention is called to Appendix B (PDP-9 ASCII-Hollerith Correspondence) for a
delineation of legal Hollerith codes and their corresponding ASCII graphics.
b.

Image Alphanumeric (Mode 3) (S2 1O locations required to store an SO-column card)
Eighty card columns are read and interpreted as Hollerith data, mapped into the

corresponding 64-graphic subset of ASCII, and stored in the user's line buffer area as
SO right-adjusted 7-bit characters, one per word, with leading zero bits. No editing
takes place (except in the case of illegal punch combinations), and no terminator is
added to the input line.
When an illegal (non-Hollerith) punch combination is encountered on the card being
read, the corresponding position in the caller's line buffer is set to contain a null (OO)
character. In addition, the parity-error bit in the I ine buffer header is raised to indicate the condition.
2.

Binary Input Modes
a.

Image Binary (Mode 1) (S2 10 locations required to store an SO-column card)
Eighty card columns are read as 12-bit binary numbers and stored one per word in

the caller's line buffer. The column data appears right-adjusted with leading zero bits.
7-35

lOPS Binary (Mode 0) (52 10 locations required to store 78 data columns)
Seventy-eight card columns (columns 1 through 78) are read as 12-bit bytes and

stored, 3 bytes in each 2-word group, in the caller's I ine buffer area. Punches
appearing in columns 79 and 80 are ignored in this mode.
Data punched on the card are taken to represent full 18-bit words, each divided
into one 6-bit segment and one 12-bit segment. The high-order (leftmost) bit in each
column appears in the 12-row of that column; the low-order bit is punched in the 9-row.
The organization of words on the card is represented schematically in Figure 7-2.

123456789
12

;;;

"0 - -'"
...
N

77 78

...

'" '" '"
;;;

'"
4

(1)

;;;
;;;

'" '"

u;
;;;

'" '"

a ... a, a ... ;;;

()O

...

~
~~~'~

HEADER
PAIR

Figure 7-2

DATA
PAIR #1

DATA
PAIR #2

DATA
IGNORED
PAIR#25

lOPS Binary Input Card Format

The line header pair, punched in columns 1,2, and 3 of the card, consists of a
header word (word 1) and a checksum word (word 2).
Header word 1 (column 1; column 2, rows 12-3) includes the following data fields:
Bit 0 (column 1, row 12): Ignore checksum indicator; may be punched.
Bits 1 through 8 (column 1, rows 11 through 6): Word Pair Count; must be punched.
The handler will halt data transfer upon fulfillment of (1) the word count in the .READ
sequence, (2) the word pair count in the card, or (3) 52 10 words transferred, whichever
occurs first.
Bits 9 through 11 (column 1, rows 7 through 9): Rows 7 and 9 must be punched.

7-36

Bits 12 through 13 (column 2, rows 12-11): Validity Code. This field is ignored by
the handler (except for checksum computation) and the punches appearing in it are not
passed on to the caller. The handler sets this field in the user's line buffer as dictated
by conditions resulting from the read request.
Bits 14 through 17 (column 2, rows 0-3): Mode; this field may contain either no
punches or punches in rows 0 and 3 to indicate logical end-of-file. If rows 0 and 3
are punched, columns 4 through 80 are ignored.
Header word 2 (column 2, rows 4-9; column 3) includes only, in bits 0 through 17,
the checksum word for the card. The checksum must be the 2's complement of the 18-b it
unsigned, arithmetic sum of all the data word (columns 4 through 78) on the card and
word 1 of the header.
c.

Dump (Mode 4) (52 10 locations required to store 78 data columns)
Identical to lOPS Binary (2 .b) I except that no header pair appears on the card.

Recoverable Errors

Reader Not Ready (Monitor Error Code 4)
a.

Hopper Empty

Stacker Fu II

Feed Check (may be hardware failure)

Read Check (may be hardware failure)

Reader not ready:
(1)

Stop button depressed.

(2) Start button not depressed.
(3) Validity check with validity button on.
D.

Unrecoverable Errors

Illegal Function (Monitor Error Code 6)
a.

.ENTER

.CLEAR

• WRITE

• TRAN

7-37

2•

III ega I Data Mode (Mon itor Error Code 7)
a.

CDA.: Not applicable; all modes are legal for this version.

COB, CDC.: lOPS ASCII only is legal for these versions. A request for data trans-

fer in any other mode results in an error return to the Monitor.
E.

Program Size
1.

CDA. (All modes): Approximately 450 10 locations

COB. (lOPS ASCII only}: 411 10 locations.
CDC. (lOPS ASCII only): Approximately 270 10 locations.

3.
F.

Program Descriptions
Both CDA. and COB. utilize 80-word internal buffers for the temporary storage of column

data as it is encountered; remapping in these two handlers is performed after all 80 columns have been
read. This scheme guarantees protection against data loss resulting from the service requirements of
other active I/o devices. CDC., on the other hand, remaps each column as it appears, thus doing
away with the need for 80 words of temporary storage. There is some, though sl ight, possibil ity of data
loss in the process, since the column data is presented at fixed time intervals which cannot be programspecified. If data loss does occur during reading, the checksum error indicator is set in the val idity
fie Id of the header for the Iine in wh ich loss was detected.
CDC. is designed for use with programs which have large core requirements but relatively
low I/o rates (for example, FORTRAN 4, MACRO).
Determination of the end of a card deck is performed as follows by CDA, CDB and CDC: on
both the CR01E and CR02B, the presence of an EOF card (all l's in column 1) signals the handler that
an EOM (End-of-Medium) condition exists. The handler appropriately returns an EOM header (1006
in word O) to the ca II i ng program.
An alternative method exists on the CR02B. The EOF button, if depressed with the hopper
empty, is interpreted as an EOM condition. Typically, as the end of a card deck is reached, assuming
no EOF card, an lOPS 4 message is output to the Teletype. Depressing the EOF button on the card
reader and striking tR on the Teletype signal the end of the card deck.

10K (DISK)
A.

Functions
1•

• IN IT

(a) Return standard line buffer size (255 10)
(b)

.SETUP - API channel register 478

7-38

(c) Set direction switch (input or output).
NOTE
In order to change transfer direction when operating in
a file oriented environment, a new. IN IT must first be
executed •
2.

• OPER (.DLETE)
(.RENAM)
(.FSTAT)
(a)

• DLETE
(1)

Examines specified Directory for presence of desired
file name. If not found, AC = 0 upon return to user.

(2)

Deletes file name (clears to 0) from the Directory of
the specified un it.

(3) Clears file bit map corresponding to deleted entry.

(b)

(4)

Clears corresponding occupancy bits in Directory bit
map.

(5)

Records modified Directory and file bit map block on
specified unit.

.RENAM
(1)

Examines specified Directory for presence of desired
file name. If not found, AC = 0 upon return to user.

(2) Changes file name in Directory to new one specified
by user program (no change is made to first block
pointers) •
(3)

(c)

Records modified Directory on specified unit.

.FSTAT
(1)

Examines specified Directory for presence of desired
file name. If not found, AC = 0 upon return to user.
If found, AC = first b lock number of fi Ie. Also, bits
0- 2 of CAL ADDRESS + 2 = 1 = Disk Directory type.

(d) Other • OPE R codes are illega I •
3.

.SEEK

(a)

Loads into core the Directory of the unit specified if the
Directory is not already in core.

(b) Checks for presence of named file. (Error return to Monitor
if not found.)
(c) Begins transfer of first block of file into handler buffer area,
overlaying Directory Entry Section but not Directory Bit Map.
(d)

Declares unit to be file oriented.

7-39

.ENTER

(a)

Loads into core the Directory of the unit specified if the
Directory is not already in core.

(b) Checks for presence of named file. If present I pointer to
that entry is saved for update at ~C LOSE time. If not present I
empty slot is found for file name insertion at .CLOSE time.
(c) Examine Directory Bit Map for free block and saves that block
number for first transfer out and for insertion in Directory Entry
Section at .CLOSE time.
(d)
5.

.CLEAR

Dec lares unit to be fi Ie oriented.

(a) Zero's out Fi Ie Bit Map blocks (71 through 77) on specified
DISK unit.

(b) Initializes DISK Directory block 100 to indicate that eight
blocks (71 though 100) are occupied.
6.

(a) On input I clears internal program switches. On output I writes
2-cell EOF line as last line in output buffer (lOPS ASCII and
binary only) and outputs last data buffer with the datd link
= 777777.
(b)

Loads into core the file bit map corresponding to the Directory
Entry in order to clear the Directory Bit Map of bits for blocks
formerly occupied by this file.

Loads Directory into memory I enters new entry and records
Directory again with new entry and updated Directory Bit Map.

(e) Clears internal program switches.
7.

MT APE (REWIND)
(BACKSPACE)

(a) REWIND
(1) Sets internal switches such that data transfer will begin
at block O.
(2)

Declares the unit as non-file-oriented I i.e. I data will
be recorded (starting at block 0) every fifth block. Five
passes will record all 1100a blocks of a DISK unit.

(b) BACKSPACE
(1)

Decrements the internal pointer to the next block to be
transferred.

.READ

(a) Input line from DISK handler buffer or block of data to user
area. (See B below for data modes.)

(b) Initiate input of next DiSK block when preceding block has
been emptied.

7-40

11.

.WRITE

(a) Transfers line or block of data from user area to DISK handler
buffer.
(b) Outputs buffer when full, examining Directory Bit Map for
free block number to store as Data link (word 3778 ) of current block output.

12.

.WAIT

Allow previous transfer to be completed before allowing user
program to continue.

13.

.TRAN

Transfer (in or out) the number of words specified by the user's
word count to/from the core area indicated in the. TRAN
macro to/from the specific block{s) desired by the user. Data
will be transferred to/from contiguous DISK blocks in the
forward or reverse direction (also declared by the user). On
input, transfer stops on word count overflow. On output,
transfer also stops on word count overflow; however, if the
word count is not equivalent to an integral number of DISK
blocks, the remainder of the last block will be filled with
zeros.

Lega I Data Modes

lOPS ASCII

lOPS Binary

Image Alphanumeric

Image Binary

Dump

Unrecoverable Errors

Illegal Function

Monitor Error Code 6
(a) See D below for illegal functions.

Illegal Data Mode

Monitor Error Code 7
(a)

.SEEK with .INIT for output

(b)

.ENTER with .INIT for input

File Still Active

Monitor Error Code 10
(a)

.SEEK, .ENTER
Not Executed

File Not Found

.SEEK, .ENTER, .CLEAR or .OPER when last file has not
been closed.
Monitor Error Code 11

(a)

.READ or .WRITE executed prior to .SEEK or .ENTER (or
.MTAPE - REWIND).
Monitor Error Code 13

(a) File name not found in Directory on a .SEEK.

7-41

DISK Directory
Full

Monitor Error Code 14
(a) Directory Entry Section found full on an .ENTER
Monitor Error Code 15

DISK Unit full

(a) All DISK unit blocks occupied on a .WRITE

Output Buffer
Overflow

Monitor Error Code 16
(a) Output line (lOPS ASCII or Binary) greater than 255 '0 cells
(inc luding header).

(b) Output block (Image Binary or Image Alphanumeric greater
than 255 '0 cells (excluding header).
9.

10.

Excessive Number
of Files Referenced

Monitor Error Code 17

Disk Failure

Monitor Error Code 20

See Section 0 for file reference limitations.

(a) Disk hardware malfunction
1l.

Illegal Disk
Address

Monitor Error Code 21
(a) Reference to protected track
(b) Reference to nonexistent track

12.

13.

14.

Two Output Files
on Same Unit
Illegal Word
Pair Count (WPC)

Monitor Error Code 22
(a) Two output files open simultaneously on the same unit.
Monitor Error Code 23
(a) WPC = 0, or greater than 177

Illegal Disk Unit

Monitor Error Code 27
(a) Attempt to reference disk unit 3 or 7

Subprogram Description and Size
1.

DKA (which requires 2272 ,0 locations)
DKA is the most general DISK handler issued with the PDP-9 ADVANCED Software
System. DKA has a simultaneous 3-file capacity, either input or output. Files may
be referenced on the same or different DISK units except that 2 or more output files may
not be on the same unit. All data modes are handled as well as all lOPS functions
(except .MTAPE). Three 256 ,0-word data buffers, three 32 ,0-word Directory Bit Maps
and three 32 ,0-word File Bit Maps are included in the body of the handler.

DKB (which requires 1533 10 locations)
DKB has a simultaneous 2-file capacity: one input; one output. Both files may be on
the same or different units. DKB transfers data only in lOPS ASCII or lOPS binary data
modes. Included in the handler is space for two 256 ,0-word data buffers, one 32 10word Directory Bit Map and one 32 1O-word File Bit Map. Functions included are:
7-42

.ENTER
.CLOSE

.INIT
.SEEK
3.

.READ
.WRITE

. WAIT

DKC (which requires 645 10 locations)
DKC is the most limited (and conservative in terms of core allocation) DISK handler in
the PDP-9 ADVANCED Software System. DKC is a READ ONLY handler with a 1-file
capacity requiring no space for bit maps and only one 256 10-word DISK data buffer
to handle either lOPS ASCII or lOPS binary input (and no other). Functions included
are
.INIT
.SEEK

.CLOSE
.READ

.WAIT

DKD (which requires 1533 10 locations)
DKD has full lOPS function capabilities; however, it allows for one and only one fi Ie
reference, either input or output, at any given time. Sequential file references are
permitted. All data modes are acceptable to DKD. One 256 10-word data buffer, one
32 10 -word Directory Bit Map and one 32 10 -word File Bit Map are included. DKD. is
the only DISK handler which allows .MTAPE transfers.

DR (DRUM)

A. Functions

.INIT

(a)

Return standard line buffer size (255 10).

(b)

.SETUP - API channel register 468 .

(c)

Set direction switch (input or output).
NOTE
In order to change transfer direction when operating in
a file-oriented environment, a new .INIT must first be
executed.

.OPER (. DLETE)
(.RENAM)
(.FSTAT)
(a)

.DLETE
(1) Examines specified Directory for presence of desired
fi Ie name. If not found, AC = 0 upon return to user.
(2)

Deletes file name (clears to 0) from the Directory of
the specified unit.

(3) Clears file bit map corresponding to deleted entry.
(4) Clears corresponding occupancy bits in Directory bit
map.

7-43

(5) Records modified Directory and file bit map block on
specified unit.
(b)

.RENAM
(1) Examines specified Directory for presence of desired
file name. If not found, AC = 0 upon return to user.
(2) Changes file name in Directory to new one specified
by user program (no change is made to first block
pointers) .
(3) Records modified Directory on specified unit.

(c)

.FSTAT
(1 )

Exami nes spec ifi ed Directory for presence of desi red
file name. If not found, AC = 0 upon return to user.
If found, AC = first block number of fi Ie. Also, bits
o - 2 of CAL ADDRESS + 2 = 1 = Drum Directory type.

(d) Other .OPER codes are illegal.
3.

.SEEK

(a) Loads into core the Directory of the unit specified if the
Directory is not already in core.
(b) Checks for presence of named file. (Error return to Monitor if not found.)
(c)

Begins transfer of first block of file into handler buffer
area overlaying Directory Entry Section but not Directory
Bit Map.

(d) Declares unit to be file-oriented.
4.

.ENTER

(a) Loads into core the Directory of the unit specified if the
Directory is not already in core.
(b) Checks for presence of named file. If present, pointer to
that entry is saved for update at .CLOSE time. If not
present, empty slot is found for file name insertion at
.CLOSE time.
(c) Examines Directory Bit Map for free block and saves that
block number for first transfer out and for insertion in
Directory Entry Section at .CLOSE time.
(d) Declares unit to be file oriented.

.CLEAR

(a) Zero's out File Bit Map blocks (71 - 77) on specified
Drum unit.
(b) Initializes Drum Directory block 100 to indicate that eight
blocks (71 - 100) are occupied.

(a) On input, clears internal program switches. On output,
writes 2-cell EOF line as last line in output buffer (lOPS
ASCII and binary only) and outputs last data buffer with
the data Ii nk = 777777 •

7-44

(b)

Loads into core the file bit map corresponding to the
Directory Entry in order to clear the Directory Bit Map of
bits for blocks formerly occupied by this file.

(c)

Records newly constructed fi Ie bit map.

(d)

Loads Directory into memory, enters new entry and records
Directory again with new entry and updated Directory Bit
Map.

(e) Clears internal program switches.
7.

MTAPE (REWIND)
(BACKSPACE)

(a)

REWIND

(1) Sets internal switches such that data transfer will begin at block O.
(2)

(b)

Declares the unit as non-fi Ie-oriented, i.e., data
will be recorded (starting at block 0) every fifth
block. Five passes will record all 11008 blocks of a
Drum unit.

BACKSPACE

(1) Decrements the internal pointer to the next block to
be transferred.
(c) Other. MTAPE functions are ignored.

10.

.READ

(a)

Input line from Drum handler buffer or block of data to
user area. (See B below for data modes.)

(b) Initiate input of next Drum block when preceding block
has been emptied.

11.

. WRITE

(a) Transfers line or block of data from user area to Drum
handler buffer.
(b)

Outputs buffer when full, examining Directory Bit Map for
free block number to store as Data Link (word 3778) of current block output.

12.

.WAIT

Allow previous transfer to be completed before allowing
user program to continue.

13.

. TRAN

Transfer (in or out) the number of words specified by the
user's word count to/from the core area indicated in the
•TRAN macro to/from the specifi c block(s) desired by the
user. Data wi II be transferred to/from contiguous Drum
blocks in the forward or reverse direction (also declared
by the user). On input, transfer stops on word count overflow. On output, transfer also stops on word count overflow; however, if the word count is not equivalent to an
integral number of Drum blocks, the remainder of the last
block wi II be fi lied with Os.

7-45

B. Legal Data Modes

lOPS ASCII

lOPS Binary

Image Alphanumeric

Image Binary

Dump

C. Unrecoverable Errors
1.

Monitor Error Code 6

I"egal Function

(a) See D below for i"egal functions

2•

I" ega I Data Mode

Monitor Error Code 7
(a)

.SEEK with .INIT for output

(b)

.ENTER with .INIT for input

Monitor Error Code 10

File Still Active
(a)

.SEEK, .ENTER
Not Executed

File Not Found

.SEEK, .ENTER, .CLEAR or .OPER when last file has not
been closed.
Monitor Error Code 11

(a)

.READ or .WRITE executed prior to .SEEK or .ENTER (or
.MTAPE - REWIND).
Monitor Error Code 13

(a) File name not found in Directory on a .SEEK

Drum Directory
Fu"
Drum Unit Fu"

Monitor Error Code 14
(a) Directory Entry Section found full on an • ENTER
Monitor Error Code 15
(a) A" Drum unit blocks occupied on a •WRITE

8•

Output Buffer
Overflow

Monitor Error Code 16
(a) Output line (lOPS ASCII or Binary) greater than 255 10
cells (including header).
(b) Output block (Image Binary or Image Alphanumeric greater
than 255 10 cells (excluding header).

10.

Excessive Number
of Files Referenced
Illegal Drum Sector
Address

Monitor Error Code 17
See Section D for file reference limitations.
Monitor Error Code 25
(a) Sector address greater than physi cal drum size.
(b) For unit 1 or greater, sector address greater than 7778

11.

Illegal Drum Size

Monitor Error Code 35

7-46

(a)
12.

13.

14.

Two Output Files
on Same Unit
Illegal Word
Pair Count (WPC)
Illegal Drum Unit

.SCOM + 4, Bits 15 - 17, not set up (1-5)
Monitor Error Code 22

(a) Two output files open simultaneously on the same unit.
Monitor Error Code 23
(a) WPC = 0, or greater than 177
Mon i tor Error Code 26
(a) 32, 65 or 131K Drum: Unit #> 0
(b) 262K Drum: Unit #> 1
(c) 524K Drum: Unit #> 3

D. Subprogram Description and Size
1.

DRA (which requires 2288 10 locations)
DRA is the most general Drum handler issued with the PDP-9 ADVANCED Software
System. DRA has a simultaneous 3-file capacity, either input or output. Files may
be referenced on the same or different Drum units except that 2 or more output files
may not be on the same unit. All data modes are handled as well as all lOPS functions
(except .MTAPE). Three 256 10-word data buffers, three 32 10 -word Directory Bit Maps
and three 32 1O-word File Bit Maps are included in the body of the handler.

DRB (which requires 1473 10 locations)
DRB has a simultaneous 2-file capacity: one input, one output. Both files may be on
the same or different units. DRB transfers data only in lOPS ASCII or lOPS binary data
modes. Included in the handler is space for two 256 1O-word data buffers, one 32 10 word Directory Bit Map and one 32 10 -word File Bit Map. Functions included are
.INIT
.SEEK

.ENTER
.CLOSE

.READ
•WRITE

.WAIT

DRC (which requires 601 10 locations)
DRC is the most limited (and conservative in terms of core allocation) Drum handler in
the PDP-9 ADVANCED Software System. DRC is a READ ONLY handler with a 1-file
capacity requiring no space for bit maps and only one 256 1O-word Drum data buffer to
handle either lOPS ASCII or lOPS binary input (and no other). Functions included
are:
.INIT
.SEEK

.CLOSE
.READ

.WAIT

DRD (which requires 1478 10 locations)
DRD has full lOPS function capabilities; however, it allows for only one file-reference,
either input or output I at any given time. Sequential file references are permitted.

7-47

All data modes are acceptable to DRD. One 256 10-word data buffer, one 32 1O-word
Directory Bit Map and one 32 10-word File Bit Map are included. DRD. is the only
Drum handler which allows .MTAPE transfers.

IMT (MAGNETIC TAPE)/
A. Functions
1.

.INIT

(a) Return standard buffer size (255 10).
(b) Call .SETUP - API Channel Register 458 •

(c) Ensure that the referenced transport is not currently open for
output transfers in the fi Ie-structured environment. If the
drive is not open for writing or is non-file-structured, continue.
If the drive is open for output and is fi Ie-structured, overlay
the first block (header label) with a logical end-of-tape
indicator.
(d) Set transfer direction (input or output).
(e) Indicate that the decision with respect to file-structuring has
not been made.
(f)

If first .INIT to this unit, assign default parity, density, and
track-count settings for this unit. Parity is odd, density is
800 BPI, and track-count is specified by bit 6 of .SCOM + 4
(0 = 7-channel, 1 = 9-channel).

(g) Indi cate that the referenced drive is open for I/o transfers.
2.

.OPER (.DLETE)
(.RENAM)
(.FSTAT)
(a)

.DLETE

(1) Examine the directory on the referenced unit for a file of
the name provided. If no file is found, return to the user
with the AC = O.
(2) If fi Ie is found, remove the name found from the Directory,
zero the applicable accessibility bit, decrement the active
fi Ie count, and re-record the Directory.
(3) Return with the AC 10.

(b)

.RENAM
(1) Search the Directory for an active file of the name given.
If no fi Ie is found, return to the user with the AC = O.
(2) If file is found, replace the Directory file name entry with
the new fi Ie name and re-record the Directory.
(3) Return with the AC 10.

7-48

(c)

.FSTAT
(1) Set bits 0 through 2 of CAL + 2 = 4.
(2) Search Directory for a fi Ie of the name given. If no file
is found, return with the AC = O.
(3) If a file is found, return with the AC = relative position
of the file on tape (1 through 3748 ).

.SEEK

(a) Determine if the referenced unit is file-structured. If it is
not, take error return (lOPS 7). If no decision has been made,
declare the unit file-structured.
(b)

Ensure that no fil e is open on the referenced unit. Take error
return (lOPS 10) if so.

(c) Ensure that the referenced unit has been .INIT'ed for input.
Take error return (lOPS 7) if not.
(d) Search directory for a fi Ie of the name given. If no file is
found, error return (lOPS 13) to Monitor.
(e) Physically position the tape to read the first data block on the
file. The handler-calculated file name must match the file
name in the header label (lOPS 40 if not).
(f)
4.

.ENTER

Indicate a file open for reading on the referenced unit.

(a) Determine if the referenced unit is fi Ie-structured. If it is not,
take error return (lOPS 7). If no decision has been made,
declare the unit to be file-structured.
(b) Ensure that no file is open on the referenced unit. Take error
return (lOPS 10) if so.
(c) Ensure that the referenced unit has been declared an output
unit. Error return (lOPS 7) if not.
(d) Ensure that space is available in the File Name Entry Section
of the Directory for this file name. Take error return (lOPS
14) if not.
(e) Ensure that space is available in the Accessibility Map for
this file. Take error return (lOPS 42) if not.
(f)

.CLEAR

Indicate that a file is open for writing on the unit referenced.

(a) Determine if the referenced unit is file-structured. If not,
take error return (lOPS 7). If no decision has been made, declare the unit file-structured.
(b) Rewind and write an empty File Directory at the front of the
tape, along with a Logical End-of-Tape indicator.

.CLOSE

(a) Input: Indicate that the referenced unit is no longer available for I/o transfers; return to caller.
(b) Output:
(1)

Non-File-Structured Tape: Write two end-of-file markers,

7-49

then backspace one to position the recording head between the two EOF markers written. Indicate that unit
is no longer open for I/o transfers, and return to caller.
(2) File-Structured Tape

Write the partial data buffer, if one is present.

Write trailer label and logical end-of-tape indicator.

Search the File Directory for a name identical to
that of the file being closed. If one is found, remove it from the directory and set its accessibility
bit to zero.

Add the new fi Ie name at the bottom of the Directory •

Update total and active fi Ie counts.

Re-record the Directory.

Indicate that unit is no longer open for I/o transfers,
and return to call er.

.MTAPE
(a)

Determine whether unit if fi Ie-structured; if so, take error
return (lOPS 7). If no decision has been made, declare unit
non-fi Ie-structured.

(b)

Honor subfunction specification as follows:
00

Rewind: Issue rewind to drive specified.

Undefined: Error Return (lOPS 6).

Backspace Record: Issue a single backspace to the drive
specified.

Backspace File: Backspace until two EOF markers have
been passed in reverse, then space forward one record.

Write EOF: Write one EOF marker.

05 Space Forward Record: Issue a single space forward to
the drive specified.

06 Space Forward File: Space forward until a single EOF
marker is passed.

07 Space to Logical EOT: Space forward until two consecutive EOF markers are passed, then backspace one record.
10
through
17

Describe Tape Configuration: Update the tape format
descriptor bits for the drive specified. Subsequent I/O
transfers (including space) will be performed in the density, parity, and channel-count given in .MTAPE 1017, thus:

7-50

Subfunction

Channel
Count

Parity

Density

Even

200 BPI

Even

556 BPI

Even

800 BPI

Odd

200 BPI

Odd

556 BPI

Odd

800 BPI

Even

800 BPI

Odd

800 BPI

.READ
(a)

Ensure that referenced unit is input. lOPS 7 if not.

(b)

Ensure that a file is open for reading or unit is non-filestructured. lOPS 11 if not.

Read Errors
(1) Parity/Checksum Errors - As described in Section 5.9.4.
(2)

EOF Encountered.
a.

File-Structured Environment.
Modes 0 - 4: An EOF pseudo-line is constructed
and stored in the user's Iine buffer area. The format
of the 2-word line is as follows:
Header word 0: 001005
Header word 1: 776773
Mode 5: Illegal in file-structured environment.

Non-Fi Ie-Structured Envi ronment.
Modes 0 - 3: An EOF pseudo-line is constructed
and stored in the user's line buffer area. The format
of the line is as follows:
Header word 0: 001005
Header word 1: 776773
Data word 0:
000000
Data word 1:
Unchanged
Modes 4 - 5: No indication of End-of-File is
currently provided.

(3)

EOT Encountered
a.

File-Structured Environment.
Modes 0 - 4: An EOM pseudo-line is constructed
and stored in the user's Iine buffer area. The format
of the 2-word line is as follows:
7-51

Header word 0: 001006
Header word 1: 776772
Mode 5: Illegal in file-structured environment.
b.

Non-File-Structured Environment.
Modes 0 - 3: Exactly as described for file-structured environment (3a above).
Modes 4 - 5: Error return (lOPS 43).

.WRlTE
(a) Ensure that referenced unit is output. lOPS 7 if not.
(b)

Ensure that a file is open for writing or that unit is non-filestructured. lOPS 11 if not.

EaT: When physical End-of-Tape is encountered during
writing, an error return (lOPS 15) is made to the Monitor.
Before control is given to the Monitor, the fi Ie being written
is added to the directory with the final two characters of the
extension as "XX".

(e) Write Errors: Continued attempts are made to rewrite the
record in error. The process terminates when EaT is encountered.
10.

.WAIT, .WAITR
(a) Check I/o underway.

11.

(1)

Busy: Return to CAL (.WAIT) or to address in CAL+2
(.WAITR).

(2)

Non-Busy: Return to CAL+2 (.WAIT) or to CAL+3
(.WAITR).

.TRAN
Honor subfunction indicator as follows:

Input Forward: Transfer next physical block on tape directly to user's buffer
area.
Output Forward: Transfer directly from user's buffer to the next physi cal block
on tape.

2, 3

Illegal; Take error return (lOPS 6) to Monitor.

Lega I Data Modes
Mode 0

lOPS Binary

Mode 1

Image Binary

Mode 2

lOPS ASCII

Mode 3

Image Alphanumeric

7-52

Mode 4

Dump

Mode 5

9-Channel Dump (Legal for 9-channel transports only)

lOPS Binary (Mode 0)
(a) Output
(1) File-Structured Tape
An attempt is made to pack the binary line into a 2571O-word buffer internal
to MTA. If the line will not fit, the current contents of the buffer are written
and the line transmitted begins a new buffer. The line checksum is computed
and stored in the second word of the Iine as it appears in MTA. 's buffer; the
user's line-buffer checksum word is undisturbed. The buffer checksum (BCP
word 2) is updated. Bits 12-13 in the user's line (in MTA.'s buffer) are set to
00.
The maximum length of the line buffer, including the header pair, is 25410
words. The first word of the header is checked to ensure that the word-pair
count is less than or equal to 1778 and greater than O. A word-pair count
equal to zero or greater than 1778 results in an error return (lOPS 23) to the
Monitor.
(2)

Non-File-Structured Tape
A check is made to ensure that the word-pair count is greater than zero. A
o count results in an immediate error return (lOPS 23) to the Monitor. No
check is made on the upper limit of the word-pair count; anything from 13778 is legal. The checksum is computed and stored in the second word of the
line in the user's line buffer area. Bits 12 - 13 of this first header word are
set to zero. The count of words to write is taken from the word-pair count in
the header and transfer from the user's area is initiated.

(b) Input
(1)

File-Structured Tape
The line ca II ed for is unpacked from a 257 1O -word buffer i nterna I to MT A. If
the buffer was emptied by a previous .READ, or if this .READ is the first one,
the buffer is refilled from the next physical block on tape. The line is stored
in the user's line buffer area. Transmission from MTA. 's buffer stops when
(a) the word-pair count in the input line or (b) the word count in the CAL
sequence is satisfied, whichever occurs first. In either case, the next-line
poi nter i ndi cates the true subsequent line. In case of buffer overflow, bits
12 and 13 of the first header word are raised. (If buffer overflow does occur,
the untransmitted portion of the line is no longer available to the caller.)
Whether buffer overflow occurs or not, the validity bits (12 - 13) of the first
header word are modified as follows and in the order indi cated. First, the
checksum for the line is calculated; if it is different from the transmitted
checksum, bits 12 - 13 are set to 10. Next, a check is made for successful
transfer of the entire block. In this context, "Successful Transfer" means
(a) the block was read without hardware-detected error and (b) the block
checksum (BCP Word 2) is correct. If transfer was unsuccessful, bits 12 - 13
are set to 01.

7-53

(2)

Non-File-Structured Tape
The count of words to transfer is taken from CAL sequence, and input is initiated from the next physical block on tape directly to the user's line-buffer
area. When the read is complete, the line validity bits are modified under
the following conditions and in the order indicated. First, bits 12 - 13 of
header word 0 are set if buffer overflow occurred. Next, a checksum is calculated (only if buffer overflow did not occur) and compared with the checksum read. If the two checksums differ, bits 12 - 13 are set to 10. Finally, a
check is made to ensure that the line was transferred without hardware-detected
error. If an error occurred, bits 12 - 13 are set to 01. If no errors of the types
described are encountered, bits 12 - 13 are unchanged.

Image Binary (Mode 1) - Handler activity is exactly as described for lOPS binary, above.
Headers and data are transferred in both file-structured and non-file-structured modes.
Modifications are limited to the checksum word and the validity field as outlined above.

lOPS ASCII (Mode 2) - Handler activity is exactly as described for lOPS Binary, above.

Image Alphanumeric (Mode 3)
(a) File-Structured Tape
Handler activity is exactly as described for lOPS binary, above. In the filestructured environment, headers and data are transferred and modifications, when
applicable, are carried out only on the checksum word and validity field.

(b) Non-File-Structured Tape
Image Alphanumeric Mode in the non-fi Ie-structured environment is intended to
provide the user with a facility for reading and writing on tape, the alphanumeric
character codes of his choice. The Mode 3 line appears in core following a .READ
and prior to a •WRITE as two header words and a number of data words as reflected
by the word pair count. Only the data portion of the line is transmitted to or from
the TCU, however. On output, the header pair is discarded before transfer begins;
on input, the header pair is constructed when the read is complete.
The method of transfer depends upon the characteristi cs of the tape unit referenced.
If the unit is 7-channel, then full 18-bit words are transferred. Each of the three
6-bit bytes in the PDP-9 register occupies a single 7-bit frame on the tape. If the
unit is 9-channel, then each of two 8-bit bytes (bits 2 - 9 and 10 - 17) occupies a
single 9-bit frame. Only two frames (a total of 16 bits) are transferred to or from
9-channel tape.

(1) Output
The count of words (including the header pair) in the line to be written is taken
from the first header word. Transfer is initiated directly from the user's line
buffer, beginning at the first data word.

7-54

(2) Input
The input block is read directly into the user's line buffer area, beginning at
the address which is two greater than that given in the CAL sequence. The
count given in the CAL sequence is interpreted as the maximum number, less
two, of data words to read. When the transfer is complete, a header is constructed and stored in the line buffer. Possible errors include only buffer overflow (validity bits = 11) or parity error (validity bits = 01).

Dump (Mode 4) - Dump mode is used to read into or write from specified areas of core,
under count control, without the need for line buffers. The action taken by MTA. in
honoring dump-mode .READ's and .WRITE's is identical in both file-structured and nonfi Ie-structured environments.
(a) Output
Data are taken from the core area specified in the CAL sequence and stored starting
in the next available place in MTA.'s buffer. When the buffer is filled, it is written
out and transmission to the new buffer continues until the count in the CAL sequence
is fulfilled. The partly-filled buffer, if one remains, is not written at the completion of the operation. Data are transferred in 255 1O -word increments. The dump
mode buffer as written includes the BCP for a total block length on tape of 257 10
words.
(b) Input
Data are taken from the handler buffer and stored sequentially starting at the core
location given in the CAL argument list. Transmission continues until the word
count in the CAL sequence is satisfied. If the handler buffer is emptied in the process, it is refilled from the next physical block on tape.
(c) Read/Write Errors
There is presently no facility for indicating I/o errors to the caller while dump
mode is being used.

9-Channel Dump (Mode 5) - This mode, device-dependent for 9-channel magnetic tape,
is designed to make use of all 8 data bits in each frame of tape, whereas all other modes
except 9-channel Image Alphanumeric require three frames for each data word written.
Transfers in Mode 5 require only two frames for each word stored. Only 16 bits of each
PDP-9 word, however, are read from or written on tape. Word format for Mode 5 is
shown below.

Bit Position:
Contents:

o1 2

9 10

IIIII I III IIIII I
P1 P2

7-55

Parity Bits (PO, P1): Bits 0 and 1 of the PDP-9 word are used as parity bits for the two
8-bit data bytes (DO and D1), respectively, in the low-order portion of the register.
During an output (write) transfer, these bits are ignored. The hardware generates the
proper parity for each data frame. During an input (read) transfer, these bits are set to
the actual parity values for the two data frames as read from tape.
Data Bytes (DO, D1): Bits 2 - 9 and 10 - 17 hold values of two adjacent 8-bit frames.
During reads and writes, DO is the first frame transferred. If a record containing an
odd number of frames is read, the final frame is stored in DO; D 1 is set to binary Os.
An even number of frames is always written during an output operation.
Mode 5 transfers may be performed only in the non-fi Ie-structured environment on
9-channel tape. An attempt to read or write a file-structured 9-channel tape or any
7 -channe I tape causes an error return (IO PS 7) to the Mon i tor.
Data are transferred directly between the user's buffer area and the control. No
buffering or editing of any kind is performed by MTA. On output, the exact count of
words to write is taken from the CAL sequence. On input, the count is interpreted as
the maximum number of words to read. Each. WRITE results in exactly one physical
block on tape; each. READ results in the input of one record (or as much of that record
as wi II fit).
There is presently no facility for indicating I/O errors to the caller while Mode 5 is
being used.

C. Recoverab Ie Errors
1.

Transport not ready. lOPS 4
Resu Its From:
(a) Write request with write lock.
(b) Transport off line or not dialed up.
(c) 9-Channel I/O request to 7-channel transport, and vice-versa.
Remedy:
(a)

Ready the requested magnetic tape unit.

(b) Type CONTROL R on the Teletype.

Unrecoverable Errors
1.

Illegal Function. lOPS 6
(a) Any file-structured request to a non-fi Ie-structured transport.
(b) Any non-fi Ie-structured request to a file-structured transport.

7-56

. TRAN with reverse direction specified.

(e) Additional restrictions outlined below.
2.

Illegal Data Mode

lOPS 7

(a) Mode 5 transfer request to fi Ie-structured transport.
(b) Additional restrictions outlined below.
3.

File Still Active

lOPS 10

.SEEK, .ENTER, .CLEAR, OR .OPER requested while a file is still open on the
specified unit.
4.

.SEEK/.ENTER Not Executed

lOPS 11

Before a .SEEK/.ENTER is executed, a .READ/.WRITE is requested to a transport
which has been declared file-structured.
5.

EOT Encountered on Read

lOPS 12

Physical End-of-Tape encountered during an input operation.
6.

Fi Ie Not Found

lOPS 13

During processing of .SEEK, the requested file name is absent from the File Name
Entry Section of the specified Directory.
7.

Directory Overflow

lOPS 14

During processing of .ENTER, the File Name Entry Section of the Directory is discovered to be fu II .
8.

EOT Encountered on Write

lOPS 15

Physical End-of-Tape encountered during an output operation.
9.

Output Buffer Overflow

lOPS 16

lOPS ASCII or lOPS Binary line exceed 255 10 words (including header).
10.

Too Many Files

lOPS 17

An excessive number of fi les are concurrently referenced
11.

Word Pair Count Error

lOPS 23

During a transfer in lOPS ASCII or lOPS Binary data mode, the Word Pair Count is
found to be Iess than 1 or greater than 1778 .
12.

Header Label Error

lOPS 40

During the processing of .SEEK, the handler-calculated file name is discovered to be
different from that present in the file header label.
13.

Accessibi Iity Map Overflow

lOPS 42

During the processing of .ENTER, the Accessibility Map is found to be full.

7-57

14. Directory Recording Error

lOPS 43

A write error is encountered during Directory recording.
E. Handler Description
1.

MTA.
The most general of the magnetic tape handlers, MTA. allows concurrent reference to
a maximum of three files, either input or output. All functions and data modes are
honored.

MTB.
MTB. is an input-output handler which allows concurrent reference to two files •• Transfers are honored only in lOPS ASCII and lOPS Binary data modes, and only the following functions are allowed:
.INIT
.SEEK
.ENTER

•WAIT
.WAITR

.CLOSE
.READ
. WRITE

MTC.
Designed for input operations, MTC. is a read-only handler with the capacity for
operating on a single file. Sequential file references are allowed. Transfers are
honored only in lOPS ASCII and lOPS Binary data modes. Legal functions are limited
to the following:
.INIT
.SEEK

. WAIT
.WAITR

.CLOSE
.READ

MTD.
MTD. honors all lOPS functions and data modes. Only a single file however, may be
open for transfers at any time. Sequential file references are permitted.

MTF.
Designed for the user operating in the FORTRAN environment, MTF. offers functions
and data modes limited to those required by the FORTRAN Object Time system. Data
modes include only lOPS ASCII and lOPS Binary. The device is always considered
non-file-structured. Functions honored include:
.INIT
.CLOSE

.READ
. WRITE

.WAIT
.WAITR

.MTAPE Rewind
• MT APE Backspace

MTF. allows a maximum of eight concurrently-open transports.

7-58

APPENDIX A
PDP-9 ASCII CHARACTER SET

Listed below are the ASCII characters interpreted by the PDP-9 Keyboard Monitor and system
programs as meaningful data input or as control characters.

00-37

40-77

100-137

140-177

ASCII
CHAR.

0
1
2
3
4
5
6
7
10

NUL
SOH (tA)

ETX (tC)

HT
LF
VT
FF
CR

SI (t 0)
DLE (t P)

0
P

DC2 (tR)
DC3 (t S)
DC4 (tT)
NACK (t U)

0
1
2
3
4
5
6
7

CNCL (t X)

12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

S
%
&

SS (t Z)
ESC

0
1
2
3
4
5
6
7
10

A
B
C
D
E
F

(
)
*

H
I

J
K
L
M
N

Q
R
S
T
U
V

ESC

;

<
ESC

RS (t)

/\ or t

delete (RO)

12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

*Codes 33, 176, 175 are interpreted as ESC (ALT Mode) and are converted on input to code 175 by
lOPS handlers.

A-l

APPENDIX B
PDP-9 ASCII/HOLLERITH CORRESPONDENCE

44-77

*00-37

0
1
2
3
4
5
6
7

10
11
12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

ASCII
CHAR.

NUL
SOH
STX
ETX
EOT
ENQ
ACK
BELL
BS
HT
LF
VT
FF
CR
SO
SI
DLE
DCl
DC2
DC3
DC4
NACK
SYNC
ETB
CNCL
EM
SS
ESC
FS
CS
RS
US

!
II

$
%
&
I

(
)
*
+

/
0
1
2
3
4
5
6
7
8
9
:

;

<
==

>
?

100-137

HOLLERITH
CHAR.

ASCII
CHAR.

\
11-2-8
7-8
3-8
11-3-8
0-4-8
12
5-8
12-5-8
11-5-8
11-4-8
12-6-8
0-3-8
11
12-3-8
0-1
0
1
2
3
4
5
6
7
8
9
2-8
11-6-8
12-4-8
6-8
0-6-8
0-7-8

A
B
C
D
E
F

G
H
I

J
K
L
M
N

0
P
Q
R
S
T
U
V

W
X
Y
Z
[
~

]
/\

(under
score)

HOLLERITH
CHAR.
@

4-8
12-1
12-2
12-3
12-4
12-5
12-6
12-7
12-8
12-9
11-1
11-2
11-3
11-4
11-5
11-6
11-7
11-8
11-9
0-2
0-3
0-4
0-5
0-6
0-7
0-8
0-9
c 12-2-8
11-7-8
t 0-2-8
12-7-8
0-5-8

*ASCII code 0-37 and 140-177 have no corresponding codes in the Hollerith set.

B-1

140-177
ASCII
CHAR.
@

b
c
d
e
f
9
h
i

k
I
m

n
0

p
q
r
s
t
u
v
w
x
y
z
{

----,
}

I
delete

0
1
2
3
4
5
6
7
10
11
12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37

APPENDIX C
KEYBOARD AND BACKGROUND/FOREGROUND MONITOR ERRORS

Explanation

Errors
WHAT?

Unrecognizable command

BAD DEV - IGNORED FROM ERR

Illegal device reference, for example:
A PRA 5 ,6/PPW7/DT A-5
where the command is processed and effective
up to the PPW and the remainder of the command is ignored.

BAD. OAT SLOT - IGNORED FROM ERR

Illegal. OAT slot reference, for example:
A PRA 5,6/PPA G
where the command is processed and effective
through A PRA 5,6 but ignored from there on.

BAD PRGNAM

Non-existent program name. Command
ignored.

PERMANENT. OAT SLOT - IGNORED FROM ERR

Command attempted to assign a device handler
to one of the permanent • OAT slots (-2, -3,
or -7).

BAD UNIT- IGNORED FROM ERR

Illegal unit reference (e.g., DTAX)

BAD START LOC

Illegal address given in "GET n address"
command.

SYS DEV ERR - CHECK UNIT & TRY AGAIN

Last command typed caused error condition on
system device control.

BAD COMMAND IN BATCH MODE

Illegal Batch Processor commands: QDUMP,
HALT, GET (all forms), BATCH, LOAD, DDT,
or DDTNS.

BAD BATCH DEV

Batch devi ce was not designated properly.
Should be:
CD - for card reader
PR - for paper tape reader
$JOB command not terminated by space, carriage return, or ALT MODE.

BAD $JOB COMMAND

C-l

APPENDIX D
LINKING LOADER AND SYSTEM LOADER ERRORS
The following error codes are output by the Linking Loader and by the System Loader. When
output by the Linking Loader, the errors are identified as shown below. When output by the System
Loader, the errors are identified as ".SYSLD n" instead of ".LOAD n."

Error

Meaning

• LOAD 1

Memory overflow - the Loader's symbol table and the user IS program
have overlapped. At this point the Loader memory map will show
the addresses of all programs loaded successfully before the overflow.
Increased use of COMMON storage may allow the program to be
loaded as COMMON can overlay the Loader and its symbol table,
since it is not loaded into until run time.

• LOAD 2

Input data error - parity error, checksum error, illegal data code,
or buffer overflow (input line bigger than Loader's buffer).

· LOAD 3

Unresolved Globals - any programs or subroutines required but not
found, whether called explicitly or implicitly, are indicated in the
memory map with an address of 00000. If any of the entries in the
memory map have a 00000 address, loading was not successful; the
cause of trouble should be remedied and the procedure repeated.

· LOAD 4

Illegal. DAT slot request - the. DAT slot requested was:
a. Out of range of Iega I . DAT slot numbers,
b. Zero,
c. Unassigned, that is, was not set up at System Generation
Time or (in the case of the Keyboard and Background/
Foreground Monitors) was not set up by an ASSIGN
command.
d. Or, in the Background/Foreground system, the BACKGROUND program requested a • DAT slot which called
for an I/o handler and device number which conflicted
with the FOREGROUND job's I/O.

D-l

APPENDIX E
lOPS ERRORS

Error Code

Error

Error Data

Comments

Illegal Function CAL

CAL address

The address points to a CAL which did not have
a legal function code (1 to 16) in bits 3 to 17 of
the word after the CAL.

CAL * illegal

CAL address

The instruction CAL * (Indirect) is an illegal
Monitor CAL.

. DAT slot error

CAL address

l. The .DAT slot number in Bits 9 to 17 of the
CAL was 0 I greater than 10, or less than -15.
2. The . DAT slot did not contain a handler address (no .IODEV was given for this .DAT
slot) .

Illegal interrupt

I/o status

An interrupt occurred which did not have an
active device handler associated with it.
The contents of the 10RS word at the time of the
interrupt is printed out.

Dev ice not ready
(type control R
when ready)

Illegal . SETUP CAL

CAL address

Use of .SETUP when appropriate skip not placed
in skip chain at system generation time.

Illegal handler
function

CAL address

A function (.READ,.WRITE, etc.) was issued to
a handler which is incapable of performing that
function (. READ to paper tape punch, . WRITE
to C version of handler (Read only».

Illegal data mode

CAL address

l. Illegal data mode for this version of the
handler used.
2. Use of input commands after device has been
•I NITed for output.

File still active

CAL address

Failure to close a file before another seek or
enter on the same . DAT slot.

SEEK/ENTER not
executed

CAL address

A read or write was issued without a prior SEEK,
ENTER, or MTAP command.

Unrecoverab Ie
DECtape error

DECtape status
register Band
Unit Number

DECtape error with status register B in bits 0 to
11 and the unit # in bits 15 to 17.

This error can occur whenever any not ready
condition occurs.
l. DECtape or MAGtape - unit not selected or
not write enabled.
2. Punch - out paper tape
3. Li ne pri nter - off line
4. Card reader - off line, out of cards, stacks
full, or card jam
5. Disk - massive failure
6. Drum - attempt to write on locked out area
or non-existent track, timing errors.

E-l

Error

Error Data

File not found

CAL address

The file name specified by the directory entry
section {pointer to entry is in CAL address plus 2}
was not found.

Directory full

CAL address

The directory entry section of the current device
in use is fu II .

DECtape full

CAL address

All blocks available for file storage are currently
full .

Output buffer overflow CAL address

The word pair count on the current . WRITE is
greater than 1778 ,

Too many fi Ies for
handler

CAL address

Too many files are currently open on the handler
referenced by this CAL {e.g., 4 files on DTA
will cause error while 2 files on DTD would cause
same error}.

Disk failure

Disk status
register

Disk failure with status register printed out.

Illegal disk address

CAL address

The CAL pointed to caused the disk control to
reference an illegal or write protected address.

Two output files on
one unit

CAL address

Two concurrent output files have been opened on
one unit.

Illegal Word Pair
Count

Sector address

The word pair count on the current input or output I ine equals zero or greater than 1778 ,

339 Handler called
without push down
I ist set up

CAL address

An attempt was made to use the 339 handler
without reserving an area for the push down list.

Illegal sector address

CAL address

The current read or write CAL caused an illegal
drum sector address to be used.

Illegal Drum unit

CAL address

The unit number in bits 0 to 2 of the word following the CAL is illegal for the drum size
specified in bits 15 to 77 of .SCOM + 4.

Illegal disk unit

CAL address

The unit number in bits 0 to 2 of the word after
the CAL is 3 or 7 which are both non-existent on
the Disk.

API software level
error

API status
register

An API break occurred to a software level which
did not have the appropriate transfer vector set
up in .SCOM + 12 to .SCOM + 15.

Non-existent memory
reference

Program counter Non-existent memory reference with protect mode
on without a user defined violation routine.

Memory protect
violation

Program Counter Reference to a location below the memory protect boundary without a user defined violation
routine.

Memory parity
error

Program counter Memory parity error without a user defined parity
error routine.

Error Code

Comments

E-2

Error Code

Error

Comments

Error Data

Power fail with
no skip setup

Program counter

Power low flag came up but a user defined
routine to save appropriate registers not in core.

Illegal drum size

CAL address of
first .INIT

Drum size in .SCOM + 4 (bits 15 to 17) is not
1 through 5.

Header label errors

CAL address

The internal header label for the currently
opened file is incorrect.

Accessibility map
overflow

CAL address

Too many fi les recorded on the current MAGtape.
Copy the tape to retrieve storage occupied by
unwanted fi les.

Directory recording error

CAL address

Directory cannot be recorded at the beginning of
the tape - use the utility program to re-make
the tape.

E-3

APPENDIX F
SYSTEM PROGRAM DISK AND DEC TAPE ADDRESSES

Program

Logical Block (8)
**

Disk
Track, Sector

Number of
Logical Blocks (8)

KM-9

0,0

SGEN2

1,40

KM-9 SKIP BLOCK

1,64

UPDATE

1,68

KM-9 I/o BLOCK

2,20

SYSLD

2,24

EXECUTE

2,60

FI LE BIT MAPS

2,68