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DIGITAL-8-7-S

December 1965

41 pages

Original

3.4MB

Document:	digital-8-7-s-d
Order Number:	DIGITAL-8-7-S
Revision:
Pages:	41
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/digital-8-7-s/digital-8-7-s-d.pdf

OCR Text

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PREFACE
The PDP-8 comes to the user complete with an

Although in many cases PDP-8 programs originated

extensive selection of system programs and rou-

tines making the full data processing capability

gram documentation is issued in a new, recursive

of the new computer immediately available to

format introduced with the PDP-8.

PDP-5 programs, all utility and functional pro-

each user, eliminating many commonly experienced initial programming delays.

Programs written by users of either the PDP-5 or
the PDP-8 and submitted to the users' library

The programs described in these abstracts come

(DECUS

from two sources, past programming effort on

Society) are immediately available to PDP-8

the PDP-5 computer, and present and contin-

users

Digital Equipment Corporation Users'

uing programming effort on the PDP-8. Thus
the PDP-8 programming system takes advantage

Consequently, users of either computer can take

of the many man-years of program development

immediate advantage of the continuing program

and field testing by PDP-5 users.

developments for the other.

CONTENTS?
‘

Chapter

Eggs

INTRODUCTION

DECTAPE SUBROUTINES

l-l

........................................................

Description

2-l

.................................................

2-1

........................................................

‘

Necessary Conventions

’
-

Format..................
Search Subroutine

.........

.......

Description
Definitions

2-4

......................................

2-5

.......................................

2-6

..'

.......

.................................................

2-6

3"]

...........

3—l

.........................................................

3"l

..............................................

Named File

..............

Library

.....................

3-l

................................

3"l

...............

Library System (or Skeleton System)

.........................

..............................

3-l

..............................

.....................

3"l

................................

.....................

3-l

.....................

3"l

.............................................................

3-2

System Exit
Directory

System Loader
Usage

2-2

2-4

Brief Description of DECtape Instructions

PDP-8 LIBRARY SYSTEM

.................

..............................

Errors......................i

.l .....................................

.....

Read and Write Subroutines

............................

.........................................................

3-2

Escape

.........................................................

3-2

Update

.........................................................

3-3

.........................................................

3—4

lndex

Delete

Getsys

......................................

3-4

......................................................

3-5

...........................

3-5

...................

Directory Size
Error Halts

Storage Map

.......................................................

3-6

Appendix
l

DECTAPE TRANSPORT AND CONTROL

.....................

Al-l

CHAPTER

INTRODUCTION
PDP-8 DECtape software provides the programmer

completed.

with the following three major operational

allow concurrent operation of several

materials:

Subroutines which the programmer

may easily

input-

output devices along with the DECtape.

These

programs occupy two memory pages

(4008

25610 words).

incorporate into a program

for data storage,

The program may thus effectively

The Library System was developed with several

logging, data acqui-

sition, data buffering (queueing), etc.

design criteria in mind.

First and perhaps fore—

most, the system should leave the state of the
2.

A library calling system for storing

computer unchanged when it exits.

named programs on DECtape and a
means

should be capable of calling programs by name

of calling them with a minimal

from the keyboard and allow for expansion of

size loader.

Second, it

the program file stored on the tape

Finally,

it should conform to existing system conventions,

Programs for preformatting tapes

namely, that all of memory except for the last

controlled by the content of the switch

memory page

(76008 77778), be available to

the programmer.

channels, to write block formats, to

—

This convention was established
.

exercise the tape and check for errors,

that the Binary Loader (paper tape),

and/or

future versions of this loader could reside in

and to provide ease of maintenance.

memory at all times.

Subroutine development has resulted in a series of

The PDP-8 DECtape Library System is loaded by

subroutines which will read or write any number

of DECtape blocks, read any number of 129—word

7600

blocks as l28 words (or one memory page),

the

search for any block (used by read and write or to

position the tape). These programs are assembled
with the user's program and are called by a iump
to subroutine instruction.

1710 instruction bootstrap routine that starts at
.

list

This loader calls a larger program into
memory page, whose function is to pre—

serve on

the tape, the contents of memory from

60008

75778, and then load the INDEX program

and the directory into those some locations.

The program interrupt

Since the information in this area of memory has

is used to detect the setting of the DECtape (DT)

been preserved, it can be restored when opera—

flag thus allowing the main program to proceed

tions have been completed.

while the DECtape operation is being completed.

The minimum system

tape contains the following programs:

A program flag is set when the operation has been

1-]

INDEX

UPDATE

Typing this causes the names of
all programs currently on file to
be typed out.
Allows the user to add a new
program to the files. UPDATE
queries the operator about the

program's name, its starting address, and its location in core
memory.

GETSYS

DELETE

tape and used to load the obiect program.

specified DECtape unit.

Causes a named file to be deleted

from the tape

this time the library program UPDATE is called,

the operator defines a new program file (con-

sisting of the FORTRAN Operating System and
the object program), and adds it to the library
As a result, the entire operating program

and the object program are now available on

the DECtape library tape.

The last group of programs,

Starting with the skeleton library tape, the user
can

build up a complete file of his active pro-

grams and continuously update it.
uses

One of the

of the library tape may be illustrated as

fol lows:

collection of short

routines controlled by the contents of the

the recording of timing and mark channels and

permits block formats to be recorded for any
Patterns may be written in these

blocks and then read and checked.

The programmer may

call the FORTRAN compiler from the library

tape and with it compile the program, obtain-

ing the obiect program.

The FORTRAN Oper-

switch

block length.

A program is written in PDP-8 FORTRAN that
is to be used repeatedly.

tape.

Generates a skeleton Library Tape
on a

ating System may then be called from the library

areas

of tape may be

periods of time.

Specified

l'rocked" for specified

A given reel of tape may thus

be thoroughly checked before it is used for data

storage.

These programs may also be used for

maintenance and checkout purposes.

CHAPTER
DECTAPE

SUBROUTINES

The data break facility in DECtape data transfers

DESCRIPTION

allows information to be transferred in segments

DECtape subroutines allow the programmer to

equal in size to the block capacity of the tape

read, write, or search DECtape using prewritten
and tested subroutines.

currently being used.

The routines include

129 (201

three basic subroutines:

A search subroutine which finds a

octal) 12-bit words per block (i .e.,

in certified tapes), but can be of any length

This capacity is usually

the user cares to create as long as the number

requested block on the tape and can

of 12—bit words per block is a multiple of 3.

exit with the tape moving in either

direction or stopped.
can

A mark track error detection circuit requires

This subroutine

that an identifying mark be read every six lines

be used directly by the programmer

automatically by the read and write

subroutines

the tape.

This 6-line mark track section re-

quires that data be recorded in 12-line segments
.

(12 being the lowest common multiple of 6-line
2.

A read forward subroutine which

marks and 4-line data words) which correspond

searches for the block requested and

to 3

reads data into core memory beginning

tion results in an inability to construct a block

at an indicated core

page.
a

A write forward subroutine which

beginning

The read and write

designed to work with pages 129 words in length

memory

loca-

if they were only 128 words in

length, thus

allowing the programmer to deal with tape blocks

tion.

which are effectively equal in size to a core
page.

The routines included will not read or write in
the reverse direction.

block 129 words in length, exceeding the size

subroutines included in this program have been

writes onto that block and subsequent

at an indicated core

The closest approach is the creation of

of a core page by one word.

searches for the block requested and

blocks the contents oflcore

This ”multiple of 3" restric-

whose capacity is the same as a core memory

location, from

that block and from subsequent blocks.
3.

12-bit words.

There are, therefore,

two entries to

the

read subroutine and two entries to the write sub—

Instructions can be ex-

routine.

ecuted in the main program simultaneously with

One entry deals with tape blocks re-

gardless of their size and the other entry deals

search, read, and write functions. The accum-

with 129-word blocks as if they were 128-word

ulator and link bit is preserved by the programmer

blocks (see the individual subroutines for details

and not by the DECtape subroutines.

of entry).

2-1

The subroutines are supplied as symbolic tapes

error flag and DT flag, respectively. The

occupying 400 octal words of core storage (2 suc-

flag is checked by the MMSC instruction. If

cessive pages).

this IOT instruction skips because of the error

The tapes contain no specific

error

origin and are not terminated by a dollar sign.

flag being set, a iump indirect to a register

The user positions the subroutine tape within his

containing the address MERR should be executed.

program and supplied origin information as
desires

The DT flag is checked by the MMSF instruction.
If this IOT instruction skips because of the DT

flag being set, the instruction JMP I MCOM
NECESSARY CONVENTIONS

The DECtape subroutines use the program inter-

must

be executed.

A register must be created

(on the current page) and tagged with MCOM.

rupt facility as well as the data break facility

Access by the DECtape subroutines to the dismiss

and have a user-created interrupt service routine

routine is accomplished by the execution of

and dismiss routine.

DISM.

The interrupt service routine is the section of a
program to which control is transferred at the
moment an

interrupt

occurs.

It is responsible

for preserving the states of the AC and link, de-

termining the cause of the interrupt, and trans-

ferring control to a subprogram which will process
the interrupting condition.

The dismiss routine is responsible for restoration
of the states of the AC and link, reactivation of

the prOQram interrupt system, and transfer of

control back to the interrupted program.
Due to the

critical timing of certain DECtape

functions,

it is necessary that the user construct

the interrupt service routine in such a way that
a

subroutine handling a low priority interrupt

(user assigned, non—DECtape) may itself be interru pted

The user must define DISM as an effec-

tive jump to the dismiss routine.

If the dismiss

routine is on page 0, this parameter assignment

takes the form DISM

JMP Z ?, where ? is the

address of the dismiss routine.

If the dismiss

routine is not on page 0, the parameter assign—
ment takes

the form DISM

JMP I Z R where R

is the address of a page 0 address containing the

address of the dismiss routine.

The mnemonic AUTO must be defined in the
user's program as a page 0 auto-index register

(i.e., AUTO=10).
The programming example below illustrates the

DECtape subroutine programming conventions
in the construction of the user's interrupt routines.

The tags INTR, INT, SCAT,

SRET, SAC, LINK,

SAU, LK, READ, and ERCM in this example
were

chosen at random.

as an

intercom to the dismiss routine is optional;

The use of register 5

The high-priority interrupt conditions which the
service routine should check are the DECtape

any page 0 nonauto-index register will do.

the interrupt service routine and dismiss routine

are

located on page 0, the two
references to

them need not be indirect (i .e., DISM
Z SCAT).

requires communication with the ASR 33Key-

JMP

board via the program interrupt.

This example assumes that the user

JMPI
INTR

SCAT
.

DISM

AUTO

*1000

INTR,

JMP I z 5
10

/INTERRUPT SERVICE ROUTINE
KSF

JMP INT

/SAVE THE AC

DCA SAV
RAL

/SAVE THE LINK
/CLEAR KEYBOARD FLAG

DCA LK

KCC
TAD z I

JMP READ

/RESTART INTERRUPT SYSTEM
/SAVE RETURN
/SERV|CE KEYBOARD

DCA SAC

/SAVE AC

ION
DCA SRET

INT,

RAL

DCA LINK

MMSC

/SAVE THE LINK
/SK|P ON DECTAPE ERROR FLAG

SKP

SCAT,

JMP I ERCM
MMSF
SKP'

/GO TO MERR IN DECTAPE SUBROUTINES
/SKIP ON DECTAPE DT FLAG

JMP I MCOM

/GO TO DECTAPE SUBROUTINES

CLA CLL

/INTERRUPT DISMISS ROUTINE

TAD LINK
RAR
TAD SAC
ION
JMP I z I

/RESTORE LINK
/RESTORE AC
/RESTART INTERRUPT SYSTEM
/RETURN TO INTERRUPTED PROGRAM

SAC,

LINK,

SRET,

MCOM,

/MODIFIED BY DECTAPE SUBROUTINES

ERCM,

MERR

/ERROR ROUTINE ADDRESS IN DECTAPE SUBROUTINES

SAv,

LK,

2-3

READ,

/KEYBOARD INTERRUPT HANDLER

KRB

CLA CLL
TAD LK

/RESTORE LINK
/RESTORE AC
/RETURN TO INTERRUPTED PROGRAM

RAR

TAD SAV

JMP I SRET

FORMAT

Search Subroutine

The search subroutine is used for positioning of
tape only.

The reading and writing subroutines

will use the search subroutine to find the correct

Instructions

block automatically.

The user may independ-

ently access the search subroutine for his own
purposes.

Comments

TAD B

Where B equals the number of the block being sought.

JMSIX

Where X is the address of a register containing LVSF, LVSR, or LVST.
If LVSF is used, the tape will be moving in search forward mode when
searching is completed (the instructions CLA and MMLM will stop the
tape). lf LVSR is used, the tape will be moving in search reverse mode
when the search is completed. If LVST is used, the tape will be stopped
when searching is completed.

Where E equals the address of the return location should any error occur.
The interrupt will be off and the tape will be stopped. The AC will contain a code indicating the type of error.
Where C indicates the address of the location to return to after searching
has been completed. If the main program is to be continued during
searching, this should be coded as a DlSM instruction. The interrupt will
be off when control is transferred to this address.

ZZOO

Where ZZ indicates the number of the unit to be selected (1

RETURN

The program will return to this line when searching starts. This allows
multiprocessing. During additional program breaks, the search routine
will return via the DlSM instruction. The programmer can determine
when searching has been completed by using any of the following sequences since DONE is reset to 0 after each block mark is read and to
-l (7777) when the correct block has been found.

108).

1.BZ|X
JMP?

/CM)=DONE
/NOTDONE

2. TAD I x

/C(X)

DONE
'

SZA

/DONE

JMP?

/CM)=DONE
/ORSMA
/NOTDONE

liADIX
SNA

JMP?

(If no multiprocessing is necessary this line should be coded as a JMP
to

itself.)

Read and Write Subroutines
'

Instructions

JMSI?

Comments

Where C (?) equals MRDS (generalized read), Rl28 (specialized read),
MWRS (generalized write), or W128 (specialized write). MRDS and
MWRS are subroutines which will read from or write onto blockskwithout
respect to their size. Rl28 and W128 are subroutines which deal with
l29-word blocks as if they were 128-word blocks.

Where S is the address of the first core location to be read into or written
from.

Where E equals the address of the location to be returned to in the event
The tape will be stopped and the interrupt will be turned off.

of an error.

zzoo

Where ZZ equals the number of the unit to be selected.
Where N equals the number of consecutive blocks to be read from or
written into.

Where B equals the number of the initial block to be written into or read
From

RETURN

The program will return to this line when searching starts to allow multiDuring additional program breaks and when reading or writing
has been completed, the return will be via DlSM instruction, thus this
line should never be a iump to itself. The interrupt will be on after completion. Multiprogramming takes place during the read and write functions
as well as during the search functions.

processing.

ERRORS

Should any errors occur after the subroutines are

entered, a return will be made to the main program

the following numbers in the accumulator.

Contents of Accumulator

the location indicated by the error return, with

Meaning

000l

Illegal format. Requested an illegal block.

0002

The block requested cannot be found.*

0003

The DECtape error flag was raised during searching for
other than an end-of—tape condition.*

0004

The DECtape error flag was raised during reading .**

0005

The DECtape error flag was raised during writing.**

BRIEF DESCRIPTION OF DECTAPE INSTRUCTIONS

The

only and should not be taken as a detailed de—

following description is designed as an

aid to

scription of the DECtape system.

understanding the DECtape routines
Mnemonic

Instructions

Code

MMLS

675i

MMLM

6752

Comments

DECtape select. Clears the DECtape flag. Selects the unit
designated by a 2-5 of the AC and institutes a 70-msec delay.
The DECtape flag is set at the end of this delay.
DECtape load motion. Clears the DECtape flag.

Loads the

motion register from AC bits 7 and 8 (bit 7 a I

equals GO,
equals REVERSE, bit 8 a 0
equals FORWARD). Institutes a 70-msec delay and sets the
DECtape at the end of the delay.
bit 7 a 0 equals STOP, bit 8 a l

6754

MMLF

Loads the function register from the contents of AC bits 9-I I
and then clears the AC.
no

action in regard to the

in bits 9 through

Institutes no delay and undertakes

DECtape flag. The octal number

II is coded as follows:

*The number of the block mark being searched for can be found at BLKN.
be found at TEMN

The block mark iust read can

**The number of the block being read when the error occurred can be found at TEMN.
2-6

0=Move
l

2 = Read data

MMMF

6756

Read all bits

Write data

Write all bits

Write mark and timing

DECtape load function and motion.

A microprogrammed in—

struction encompassing MMLM and MMLF.

Sets function and motion registers from AC bits 7-“, i.e.,

Read data reverse

Write data forward

MMMM

6757

Read data forward

Write data reverse

Search forward
Search reverse etc.

DECtape load select, motion, and function. Amicroprogram
of instructions MMLF,

MMC C

6762

MMLM, and MMLS.

DECtape clear memory address counter. Clears the memory
address counter.

MMLC

6764

DECtape load memory address counter. Contents of the' accumulator are transferred into the memory address counter and
then the AC is cleared.

MMML

6766

Clears and loads the memory address counter.
of MMCC and MMLC.

MMSF

676i

Skip on DECtape flag
a

A microprogram

If the DECtape flag has been set to

l, the contents of the PC are incremented by one and the

next instruction is

skipped.

Does not clear flag.

In search mode:

lf flag is set:

A block mark number has just been read and

transferred to core address contained in MAC.

Contents of

MAC remain unchanged.
In read data mode:

A block of data has iust been transferred

to core memory via data break. The control is still in read
data mode and the tape is moving. MAC contains the address

of next sequential core register following the last one read
into.

The next block on tape will be read into core beginning
MAC if no action is taken.

at current address in

2-7

In write data made:

A block of data has just been written on

The control is still in
tape from core memory via data break
write data made and the tape is moving. MAC contains the
.

address of the next-sequential core address following the last

written from. The next block on tape will be written onto.
from core beginning at current address in MAC if no action is

one

taken.

MMSC

6771

Skip on error flag.

If the error flag has been set to a l, the

contents of the PC are incremented and the next instruction is

skipped.
Encountering an end zone will set the error flag.
expect

In this case,

to see an MT flag set 70-msec after the end zone is

This is a signal to institute turn-around action
(if desired) and be assured of opening the "eyes" of the control
in time to read the black mark number of the last block encountered prior to the end zone (useful procedure when
"bouncing" off the end zone to read or write the end block).

encountered.

MMCF

6772

Clears the DECtape DT and error flags.

MMRS

6774

The condition of the status levels is transferred into bits 0
through 7 of the accumulator. The accumulator bit assignments are:

4
5

DT flag
Error flag

END (selected tape at end point)

Timing error
Reverse tape direction

Parity or mark track error
Select error

/RDP-8 DECTAPE SUBROUTINES
/"DISM“ MUST BE

DEFINED AS AN

EFFECTIVE JUMP

THE

DISMIS

ROUTINE
‘

/‘

VIA

PAGE ZERO

/"AUTO" MUST
/”MCOM" MUST

DEFINED As

THE

SOME AUTO

ADDRESS

INSTR.

JMP

WHEN

THE

INDEX

THE

TAG OF

wHEN THE INTERRUPT
INTERRUPT ROUTINE FINDS THE ERROR
/
EFFECTIVE JUMP TO "MERR" MUST BE EXECUTED
IEXAMPLE:
/

FLAG

SET.

MMSC

SKP

JMP

ERCO

/RESPONSE

DECTAPE

ERROR

MCOM

/RESPONSE

DECTAPE

FLAG

MMSF

SKP

JMP

FLAG

0....

.....

.....I

/MCOM:

/ERCO:

MERR

/SCAT:

TAD

RAR

TAD

ION

JMP

/UISM=JMP

/RESTORE LINK
/RESTURE C(AC)
I

/RETURN

MAIN

PROG

SCAT
/AUTO=10
/5EARCH ROUTINE

FORMAT:

TAD

JMS

/WHERE
X

/WHERE

/LVSR

/WHERE

CONTAINING LVSF:

LVST

E=ERROR

/WHERE

ZZOO

MULTIPHOGRAM

/SEAHCH

RETURN ADDRESS
C=COMPLETION RETURN ADDRESS
/WHERE ZZ=UVIT NUMBER (OCTAL)

LUSH:

B=BLOCK NUMBER
X 15 A REGISTER

AND LEAVE

TAPE

RETURN

MOVING

REVERSE

MODE

0
DCA

BLKN

TAD LVSR

/SEAKCH

LVST:

DCA

LVSF

JMP

LVSF+3

AND LEAVE

TAPE

BOA

bLKN

TAD

LVST

DCA

LVSF
'

CMA
DCA LUST
JMP

LVSF+2

STOPPED

FORWARD MODE

/SEARCH
LVSF:

TAPE MOVING

AND LEAVE

FORWARD MODE

DCA
IAC

BLKN

DCA

BACO

CMA
TAD
DCA

BACO
FOCO

10F

PCF

TCF
RRB
DCF

PLCF
KCC
MMCF

TAD
DCA

0N9
I MIN3

IDATA

TAD

0N1

/TEMN

DCA
TAD

DONE
CN2

xsl

DCA

DIRC

TAD

BLKN

/MCOM

MMML

SNA
JMP

FERR+1

IFORMAT

ERROR

CIA
DCA

BLKN

TAD

0N3
DRC

x7770

TAD I LVSF
DCA LVSR

/PICK

ERROR

LVSF /PICK

COMPLETION

UNIT NUMBER

/PICK

MULTI

/SET

FOR

DCA

ISZ

/CHANCE OF

COUNTER

RETURN

ADDRESS

LVSF

TAD

DCA

BACK

Isz

LVSF

TAD

DCA

UNIT

Isz

LVSF

TAD LVSF

DCA

DIRECTION

/PICK

2-10

RETURN

ADDRESS

PROGRAM RETURN
DISMIS

INITIAL

ADDRESS

TURN:

ISZ

DRC

SKP
JMP

FERR

/BLOCK

TAD

CN6
DIRC

/-21

TAD
SNA

OLA

JMP

MREV

TAD

CN7

DOA

DIRC

TAD

SPAC

DCA

SCH2

TAD

HLKN

TAD
DCA

FOCO

TAD

UNIT

TAD

DIRC

CANNOT

FOUND

/21
CLA

/SPA

DISB

MMMM

JMS

/WAIT

MING

U1 SM

DATA,

MMCF

TAD

TENN

TAD

DISB

SZA
JMP

/BLOCK

FOUND

SCH2

TAD

TEMN

TAD
SZA

BLKN

JMP

TURN

CLA

BLOCK

/OBJECT

FOUVD

CMA
DCA

DONE

ISZ

LVST

JMP

BACK

MMLM

SCHB)

/LEAVE
/STOP

MING
BACK

JMS
JMP

SPA

CLA

TAPE

MOVING

TAPE

/WAIT
/OR

OLA

SMA

(WHEN

REVERSE

DIS M
MREV:

JMP

TURN

IREVERSE

TAD

0N2

/31

DCA

DIRC

TAD

DIKC

THE

TAPE

DIRECTION
-

MMMF

JMS

TAD

SMAC

DCA

SCHB

MINO

TAD

BLKN

TAD

bACO

DCA

DISb

/WAIT

ISMA'CLA

DISM
EKGO:

/FORMAT
FEKK:

JMP

AND NOT

LVSR

FOUND

/GO

USER'S

ERROR

IAC

IAC
JMP

MIN2

/OOPS

2-H
,

ROUTINE

DIRECTION)

ICONSTANTS
CNl:
TEMN
CN2:
CNS:
0N6:
0N7:
CN9:
SMAC:

7770
7757

/-21

DATA
SMA

CLA

SPAC:
SPA CLA
/ IN TERCOMM UN 1 CATION S
REGI STERS
MING:
WAIT
MINZ:
OOPS
'MIN3:
MCOM

/VARIABLES
BLKN:
BACO:
FUCO:
DIRC:
DRC:

BACK:
UNIT}
DISB:
DONE:

TENN:

*LVSR+200

OOOOO

/PDP-8 DECTAPE
IFORMAT:
/
JMS
/

SUBROUTINES
I

2200

S=STARTING

IWHERE

E=ERROR

/WHERE

ADDRESS

B=INITIAL

BLOCK

BLOCKS

NUMBER

RETURN

ROUTINE

SZA

CN13
CLA

JMP

MENZ

TAD
CIA

TAD

CN2O
CLA

SNA

OOPS:

RETURN

MMRS

AND

IIOOO

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TAD

ERCN

TAD
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CN22

/DROR

HOOP

MMRS

DCA

MRSA

TAD

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MENZ:

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STATUS

/STOP

TAPE

WAIT

JMP

JMS

WAIT
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MIN?

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SUBROUTINE

W128:

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JMP

IEHGJ

WRITE ON

129

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MRDS

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MWRS+5

/MRD2

/GENERAL
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R128:

CORE ADDRESS

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HANDLING

MERR:

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lERROR

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AND

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/WHERE

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CLA
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CNIO

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PASS+2

JMP

MRDI

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PASS+3

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(6754)

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TAD

R128

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CHAPTER
PDP—8

LIBRARY

SYSTEM

DESCRIPTION

Library System (or Skeleton System)

The Library System was developed with several

A collection of five programs stored on DECtape.

design criteria in mind.

These programs provide for the loading of named

First and perhaps fore-

files into core memory, for the definition ofnew

most, the system should leave the state of the
it

named files, for the deletion of named files,

should be capable of calling programs by name

and for the creation of a new Library System

from the keyboard and allowing for expansion

The Library System is loaded by the System

of the program file stored on the tape.

Loader.

computer unchanged when it exits.

Second,

Finally,

it should conform to existing system conventions;

Library

namely, that all of memory except for the last
memory page

—

the programmer.
so

The sum of user-defined named files and the

(76008 77778) be available to

Library System

This convention was established

System Exit

that the Binary Loader (paper tape) and/or

future versions of this loader could reside in

When the Library System has loaded a named

memory at all times.

file into care memory, it restores all of
memory

that it occupied and it restores the System Loader
With these ideas in mind, the PDP-8 DECtape

Library System
a

Binary Loader to their normal locations.

This is called System Exit.