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DIGITAL-7-22A-IO

January 1966

26 pages

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Document:	DECTAPE Subrts
Order Number:	DIGITAL-7-22A-IO
Revision:
Pages:	26
Original Filename:	http://bitsavers.org/pdf/dec/pdp7/DIGITAL-7-22A-IO_DECTAPE_Subrts_Jan66.pdf

OCR Text

IDENTIFICATION

1.1

Di gi ta 1-7-22A-I/O

1.2

Bidirectional PDP-7 DECtape Subroutines

1.3

January 21, 1966

PDP

LIBRARY

Dig ita 1-7- 22A -1/ 0
Page 1

ABSTRACT

The Bidirectional PDP-7 DECtape Subroutines allow the programmer to transfer variable
length records to or from DECtape in either direction depending on the current position of the tape. The
only requirement is that the standard DECtape format be used (11 OOa usable blocks of 400a words each).
Mainly the subroutines minimize access time to the DECtape, and allow program overlap with data transfers using the program interrupt or automatic priority interrupt facilities. With three exceptions,* the
subroutines are completely compatible with the unidirectional subroutines described in Digital-7-22-I/O
(which are not obsolete). Information written with either set can be read with the other. In addition,
data is written as if it were in the forward direction; so that the record need not be read in the same direction as it was written. The amount of data transferred need not be an integral number of blocks.
Though the routines themselves are loaded into the first aK of core, data transfers can address normal or
extended memories. These new subroutines make more efficient use of the DECtape; however, as they
are significantly larger than the basic set (450 locations for the unidirectional, 604 locations for the
bidirectional), the user must choose the set most applicable to the job.

REQUIREMENTS

3. 1

Storage

The subroutines occupy approximately 604a locations including variable registers and literals,
and must be loaded into the first aK of memory.
3.3

Equipment

. The subroutines function with a 555 or TU55 DECtape drive and a 550 or 550A DECtape
control interfaced to a PDP-7. The subroutines will not run on a PDP-4.

USAGE

4.1

The subroutines are in ASCII format designed to be assembled as part of the user1s program.
The tapes contain no origin, no starting address, and no undefined symbols. In order to link with the
user1s program, however, the following items are required as part of the main program.

4.1.1

In order to correctly use the program interrupt or automatic priority interrupt facilities, the
main program must include the following coding. Reference should be made to the description of the interrupt faci lities in the PDP-7 Users Handbook (F-75).

For the standard program interrupt control, the main program should store a JMP X instruction
at location 1 where X must include the following instructions:

* 1) The Search subroutine can no longer be used as a separate independent subroutine.
2) The register MMWA 1 no longer holds the next block to be transferred (or the next free block). See
Section 4.2.7, page 5.
3) Starting and ending core addresses for the Read and Write Subroutines must be lS-bit addresses and
can no longer be LAW instructions.

Digitol-7-22A-I/O
Page 2

DAC ACSAVE
MMEF
SKP
JMP I MMERR
MMDF
SKP
JMP I MMDATA
MMBF
SKP
JMP I MMBLF
(Any addit"ionaloptions attached
to the interrupt are checked here)

/SAVE THE ACCUMULATOR
/SKIP ON DECTAPE ERROR FLAG
/SKIP ON DECTAPE DATA FLAG
/SKIP ON DECTAPE BLOCK END FLAG OR HLT
/IF NO OTHER OPTIONS ATTACHED

For the automatic priority interrupt ,the program should store a JMS X instruction at location 43 (assuming DECtape is attached to channel 3) where X must include the following instructions:

o
DAC ACSAVE
MMEF
SKP
JMP I MMERR
MMDF
SKP
JMP I MMDATA
MMBF
HLT

/SAVE THE ACCUMULATOR
/SKIP ON DECTAPE ERROR FLAG
/SKIP ON DECTAPE DATA FLAG
/SKIPON DECTAPE BLOCK END FLAG ERROR
/UNLES"SOTHER OPTIONS ATTACHED

JMP I MMBLF
4.1 .2
The tag "DISMIS" must be defined in the main program as a jump to the instructions which
restore the link bit and accumulator and reenable the interrupt or channel. (The examples assume the
"
interrupt routines were coded as in Section 4.1 .1 above.)

For the standard program interrupt control:
" DISMIS = JMP.
LAC 0
RAL
LAC ACSAVE
ION
JMPIO

/RESTORE LI NK
/RESTORE ACCUMULA TOR
/ENABLE INTERRUPT
/RETURN TO MAIN PROGRAM

For automatic priority interrupt:
DISMIS = JMP.
LAC X
RAL
LAC ACSAVE
DBR
JMPIX

/RESTORE LINK
/RESTORE ACCUMULATOR
/DEBREAK, ENABLE CHANNEL
/RETURN TO MAIN PROGRAM

Digital-7-22A-I/O
Page 3
4.1 .3
In order to differentiate between programs using the program interrupt and automatic priority
interrupt facil ities, the main program must contain a register named "MMAPII" containing a + 0 if the
program interrupt is used, and any nonzero word if the automatic priority interrupt is used. Since it is
not destroyed or changed MMAPII may be defined as equal to any other register which always contains
the zero or nonzero word as requ ired.
4.1.4
The subroutines assume that DECtapeis attached to channel 3 if the automatic priority
interrupt is used. If attached to any other channel, the register named "MMAPIC", within the subroutines
themselves, must be modified to contain a 1 bit in one of the bits 2-17 (representing channels 0-15
10
respectively) to indicate the channel.
For example:
If MMAPfC contains" 1"

If MMAPIC contains 11100000"
IfMMAPIC contains "40"

channel 15 is used
channel 0 is used
channel lOis used

MMAPIC need not be changed if the program interrupt, or channel 3 of the automatic priority interrupt,
is used.
4.1 .5
The program interrupt or automatic priority interrupt (and channel) will be enabled by the
subroutines themselves whether or not they were enabled by the user previously. The main program must
guarantee that no flags can come up (or be up) from devices which are not checked by the user's interrupt
service routine (as outl ined in Section 4. 1 . 1).
4.2

Call ing Sequence
To transfer information the following call ing sequence must be used:.
JMS MMRDS
LAC BLOCK
JMP XX
ZZOOOO
C1
C2
RETURN

4.2.1
writing.

lOR JMS MMWRS
/BLOCK NUM.BER
/ERROR RETURN
/UNIT
/FIRST ADDRESS
/LAST ADDRESS
/MUL TIPROGRAMMING RETURN

See Section 4.2. 1
See Section 4.2.2
See Section 4.2.3
See Section 4.2.4
See Section 4.2.5
See SectionA.2.6
See Section 4.2.7

The JMS MMRDS instruction is used for reading; the JMS MMWRS instruction is used for

4.2.2
The DECtape block number on which the information transfer is to begin can be loaded into
the accumulator with a LAC instruction as shown (where BLOCK is any register containing the correct
block number), or with a LAW instruction containing the correct block number. The user should always
assume the information is being transferred in the forward direction. As the instruction is executed, the
location cannot contain just the block number itself. The low order twelve bits of the block number are
examined, however, only block nl.)mbers 1 through 11008 are acceptable to the subrouti~es.
4.2.3
The JMP XX instruction is the instruction executed shoul d any type of error occur. The
accumulator contains a code indicating the type of error which occurred and location MMRSA contains
the status of the DECtape system (obtained by means of an MMRS instruction) at the time of the error.
The error may be detected in either the main program level or interrupt level of the program and, therefore, the interrupt system or the particular channel used will be disabled when this instruction is executed.

Disitol-7-22A-I/O
Page 4
NOTE: If the main program is normally in extend mode while the DECtape is
running, the error return must be a JMP I (XX+400000) so that the extend mode
wi II be restored if an error occurs.

At the time the instruc:tion is executed, the contents of the accumulator can be interpreted as follows:
Contents of Accumu lator

Meaning

LAW

100

Illegal format. Block number or corelocations requested were illegal.

LAW

200

Block requested cannot pe found. *

LAW

300

The DECtape error flag was raised while
searching for other than an end-'of-tClpe
condi ti on . *

LAW

400

The DECtape error flag was raised while
reading.**

LAW

500-

The ca Icu tated checksum does not agree
with the checksum read from tape. **

LAW

600

The DECtape error flag was raised while
writing.**

LAW

700

The block number read was not the block
mark number predicted, while reading or
writing. **

At the present the DECtape error flag can only. be raised by end-of-tape, a timing error
(the program di~ han~le data fast enough), or a ~ark-track error.
4.2.4
ZZ represents the unit number (1-10) which must be placed in bits 2 through 5 of the register.
Only those bits are examined.
4.2.5
C1 represents the 15-bit address of the first core location to be read into or written from
(always assuming the datciis transferred in the forward direction). It can be any address in normal or
extended memory. (Only 15 bits are examined.)
4.2.6
C2 represents the 15-bit address of the 1ast core location {inclusive} to be read into or
written from (again assuming the data is transferred in the forward direction). C2 must be equal to dI'
greater than C1. (Only 15 bits are examined.) The area transferred should not normally include the
subroutines themselves or location O. The subroutines are not designed to read over themselves.
Since each block writt~n contains its own checksum, the area read need not be the same as
that written. For example, if the user requested that locations 1000-3777 be written beginning with block
100, he could at some future time request that locations 2000-2777 be read beginning with block 102.
*The number of the block being searched -for can be found in the register called MMBLKM. The block
mark number last read can be found in the location whose address is contained in MMWA 1, (i.e., it has
been stored with a DAC I MMWA 1 instruction).
**The block number last read can be found in the location whose address is contained in MMWA 1,
{i .e., it has been stored with a DAC I MMWA 1 instruction}.

Digital-7-22A-I/O
Page 5
Any number of words may be transferred. If a nonintegral number of blocks is specified,
the following takes place:
If reading, the correct number of words wi II be deposited in memory and the
remainder of the last block wi II be read but not deposited in order to verify
the checksum.
If writing, the remainder of the last block wi II be fi lied with +O's and a correct checksum wri tten •
4.2.7
As soon as searching starts, the subroutines return to the register marked "return" with the
interrupt enabled. Ifnecessary, this allows the programmer to continue processing while both the searching and data transfer takes place. In terms of usable programming time, the user has approximately
200 msec + 53 msec per block searched + 35 msec per block transferred which can be used after the subroutines are initially called.
The register named MMDONE is set to a +0 after each block mark is passed and to -0 when
the data transfer is complete or if an error occurs. This allows the user three possible ways of determining
when the transfer has been completed:
l. ISZ MMDONE
JMP?

/NOT DONE

2. LAM
SAD MMDONE
JMP?

/DONE

3. LAC
SNA
JMP?

/NOT DONE ETC.

Method 1 has the advantage of not destroying the accumulator. However, if for any reason
the DECtape data flag did not occur as it should, the ISZ would skip incorrectly after approximately
1.4 sec.
If the user should call the DECtape subroutines before a previous DECtape transfer has been
completed, the subroutines will remain in a wait loop and not return to the main program until the first
transfer has been completed and the second has begun.
It sometimes is necessar}' to determine what is the next forward block number on the tape,
after the information just transferred. The following sequence of instructions places the correct block
number in the accumulator:
LAW 61
SAD MMWA3

/SEARCH BACK COMMAND
/LAST COMMAND ISSUED

JMP------------------------------~)

LAM -2
TAD I MMWA1

/TO SUBTRACT 3
/ADD CURRENT POSITION

(

4.3

LAC MMBLKM
ADD (1)

Switch Settings
None

/BLOCK SEARCHED FOR

Di Si to 1-7-22A -1/ 0
Page 6
4.4

Start Up andlor Entry
See Section 4.2, Calling Sequence

4.5

Errors in Usage
Only one HLT exists in the subroutines:

HLT Location
MMERRX+1

Procedure

Meaning
Error return parameter was not
'a JMP~ instruction and an error
occurred. Type 'of error is indicated by' the number in the
accumulator. (See Section 4.2.3)

Correct the calling sequence
to prov'ide a JMP instruction
for the error return.

RESTRICTIONS

None except those mentioned in the preceding paragraphs. The standard tape format of
1100a usable blocks of 400a words each must be used.

DESCRIPTION

6. 1

Discussion

The subroutines attempt to make variable length DECtape data transfers as easy and efficient as possible. They are completely self-contained, include only one possible error halt, indicate
all possible errors which can occur, and allow fastest access to the DECtape itself. The last is accomplished by keeping track of the current position of ~ach DECtape drive being used, calculating the effective starting and ending block numbers of the transfer requested, and starting the search in the direction
causing the least number of turnaro~nds. Thus the direc,tion of the data transfer is predetermined before
the tape is started and does notdeperid on the.first block actually re'ad during searching. If the tape is
currently sitting within the area to 'be used by the data transfer, the ultimate transfer direction will be
determined by which end of the DECtape area is nearest. The current position of the tape is always assumed to be the last b10ck number read ±3 blocks depending on the direction of the last transfer. Initially
a II tapes are assumed to be sitting at block number 3.
The main thing to remember is that the user 'need never worry about the actual directiontransfer of the data since data always appears in memory or on tape ~s if it were transferred in the forward
direction. For example, assuming the user has requested that locations 1000 through 1477 be written beginning at block 100, the tape appears as follows irrespective of the direction in which it was written:
~<--BLOCK 100--~)

o
o
o

Locations
1000 - 1377

(

> BLOCK 101

)
) ~ Locations -? ~300a Filler Word>
1400 -·1477
" of +0

11
34
70
70

4
7
7

Di gi ta 1-7-22A -1/0
Page 7
If the data is transferred in the forward direction, the core locations are written first in
ascending order followed by 3008 filler words. If the data is transferred in reverse, 3008 filler words
are written first followed by the core locations in descending order. In either case, the end result is the
same, and the technique is applicable to both reading and writing.*
6.2

Examples
The search routine has been rewritten:' to 'allow four different entrances:
1. Start the tape in the forward direction and 'exit when the correct block is .
found in the forward direction.
2. Start the tape in the reverse direction and exit when the correct block is
found in the reverse direction.
3. Start the tape in the forward direction and exit when the correct block is
found in the revers.e direction.
4. Start the tape in the reverse direction and exit when the correct block is
found in the forward direction.

In the following example assume the tape is sitting at the locations indicated by the letters shown, and a
request is made to transfer 20018 words beginning at block 100:

177 I 100

~ \.

101

I 102 I 103

~ ~

104

105

106

~ ..

)

Actual area used by the data
tran~fer

Case A Block 77 or less
Case B Closest to initial block
Case C Equidistant from start or end·
Case D Closest to final block
Case E Block 105 or more

The program will use entrance 1
The program will use entrance 4.
The program will use entrance 4
The program will use entrance 3
The program will use entrance 2

METHODS
See Description, Section 6.

FORMAT (Not Applicable)

EXECUTION'TfME

(Not Applicable)

*Should it ever become necessary to determine,which way a block on tape was actually written, the following method can be used. If written in the forward direction, a checksum of -0 will appear at the
front of the block (the end near the preceding lower-numbered block). If wrfttenin reverse, the -0
checksum will be at the end of the block near the next higher-numbered block.

Digitgl-7-22A-I!O
Page 8
10.

PROGRAM

10.4.

Program LJsting

PDP-? DEnTAPE SUBROUTINES
IASSUMES STANDARD 400 (OCTAL) WORD BlOCKS
ILM~
JANUARy 21, 1966
IUISMlS MUST ~E DEFINED AS JMP TO DISMISS INTERRUPT

I~I~"I~ECTrONAl

RO~T!NE

IPDP.7 D£C",TAP£,S£ARCH suSRQUTINE
MMW~:11701504

MMLC=7076riJ4
MMS!::11701644
MMRSII107612
MMDF'1I107501
M1'-1.8 F' II 1016" 1
MME:F'·707541
I'o1 MR O=107512
SKP7.703341
ASC.105502
E:PI.1i?J0044
O~R.'0!S6r211

l£'M.?07704
EEM.?07102
EMIR·707742
ILEAVE
MMSC~R,

SEAHCH REVERS£ MODE, START REV£RS~
LAW 41
IS~ARC~ FWD

OAC MMwAJ
CLA
JMP

IS,T CURR!NT DIRECTION

MMSC~8

ILEAVe: IN SEAHCH R~VERSE MODE, START FORWARD

LAW A1
IS'ARC~ REVERSE
JM.p MMSCIo!R+l'
ILEAVE IN SEARCH FORwARD MODE, START REVERSE
MMSr:R,
LAW
IS'ARC~, FORWARD
MMSR~,

SKI='

ILEAVe: IN SEARCH FORWARD MODE, START FORWARD
MMSOH~h

LAw 61

DAC MMWA3
LAM
DAC MMSSl(

TAO (1)
DAC MMSFI(
LAW MMF.:RS
OAC MMERR

LAW MMOATS
,OAe MMDATA
LAC MM8L.I<M
ADD MMEK
, SMA

ISFARCH R!VERSE, USED AS CONSTANT
IS~T CURRENT D!R£OTION
IL6AD .0, ust~ AS CONSTANT

Digital 7-22A-I/O
Page 9

JMP MMSCl-l5
LAM -,
DAr, MMSUM
135

1F't"lRMAT ERROR
IC~G

0' DyRECTION COUNTER

MILLtSECnND SELECT DELAY LOOP

MMWAtT.

MMW2.

MMRS
AND (4010)
SZA

IS4VE OONTROL TyPe: ONLY

JMP MMSC~9
LAC ~1MCHK 1..01
SAn MMSEL
JMP MMSC~9+1
DAC MMSEL
CLA
MMSE
LAM DECIMAL -5000+1
OAC MMBL..F'

INn DELAY FOR NEW DRIVES
IPTCK uP SELEOT
IP~EVIOUS SEL£OT
ISAME SELECT
IS~VE sELECT
IUsED AS cONSTANT
IS~LECT UNIT ,ERO
OCTAL
IT~MPORARy SToRAGe: AREA
11 MICROSEOONDS PER LOOP
ICnUNT 35 MILLISEcONDS
I u~, ITS ELEO TION

IS' I .'"

\.JMP

..... 1

LAC MMCHK1+1
MMSE
LAC (NOP)
DAC MMSAVE
LAC MMAPtI
SZA

JMP MMAPt

ON ApI INDICATOR
IOn ION IP NOT ON API
ITuRN nN API

ID,.CTA~E

I O~I

tSz MMSUM
SKI'

JMP MMER)(2-1
LAC MMWA3
)(OR

(2('1)

MMLC

MMSAVE,

DAe MMWA3
SAO MMSCIo4Q1
JMP MMREV
LAC MMCK3
OAe MMSC Io4 2
LAC MMBLKM
TAn MMSFK
OAe MMWA2
nZM M.. MOONE:
NOP
LAC MMR0:58+1
nAC MMSAVe:
I'S2 MMWA
F.:MIR
JM'P J MM \tJ A
LAC MMCK2
OAO MMSC~2
LAC MM9L.KM
TAO MMsBK:
JMP MMSAVE"!!2

INOT FOUND
ICURRENT SELEoT
ICnMPL£MENT DIREOTION
IS,ARCH IN CORRECT DIRECTION
ISAVE qELECTlnN
ILAW 6,

IS~T UP REVERSE O~NSTANTS
IS~A, SET TO OONTtNUE IN FORWA~D

I~ OCK

DtREcTInN

TO LOOK FOR IN THIS DIRECTION

IO~ Dl~MIS

IOtSMIS

I!MDEX POyNTER
IR,TURN TO MAIN PROGRAM
ISpA. SET TO OONTrNuE IN REVERSE DyR£cTInN

Di9ital~7-22A-I!O
Page 10
11NSTRUOTION~ ~OR

MMAP!,

AUTOMATIC PRIORITY INT~RRUPT
LAC MMAPIC
IO~CTApE C~ANN!L NUMBER

rpt

IENABL~ ApI
IENA8L~ DECTA~£

ASC

JMP MMTURN
IROUTINp':S TO ANSWER INTERHUPT
MMRS

C~ANNEL

SEQUEN~E

MMER~,

ANO

(4r7J~00)

SZA '
JMP MMTURN

LAW 300

EaT BIT

IC~ECK

IEffT, TURN AROUND
INON-EOT ~RROR CURING SEARCH

.IMP MMERx2

MMRD

OAC r M"MWA1
SAn MMWA2
JMP MM~CI-!3
OMA

ADD

MMW,A2

SMA

JM?
.JM?
SAD
JMP
JMP

LAw
,JMP

MMSAVE",1
MMTURN
MMRL.KM
t MMCHK

~'fMTUR;N

lOR SPA rOR R~VERsE
IKrrEP GOING
ITtlRN AROUND
IE~IT

TO READ OR wRITE ROuTINES

'0(}1

MM£RX2

IFnRM'AT

DECIMAL -576 OCTAL

ERROR

It::RROR LOOP

LAI.I

20~

OAC MMRLF'

MMRS
MMRSA
JMS MMROLL
LAr. MMERRX
AND (20000)

INOr" FOUND
ISTORAGE AREA

DAC

SZA
~MtR

IA~D ~OLL

CONSTANT

IJMP
IJMP

MME~RX,

CLC
DAC MMDONE
LAC MM8LI='
MMLC
JMP •

MMSEL,

MME~R,

C'I

IE~ROR

r7J

ID4TA RETuRN
ISf'OCKFLAG RETU~N
INORMAl DECTAP[ C~ANNEL.3
IPnSITtON OF' UNIT f<
IPnSITrON OF UNIT 2
IPnSITrON OF UNIT 3
IPnSITrON OF UNIT 4
IPnSITrON Or UNIT 5
IPnSITtO N OF UNIT 6

MMDATA,
MM8L~,

MMAI)TC,
MMWA)(,

I-ILT

(0000
3

3
3
3
3
3

ISTORAGE AREA
IERROR EXtT WAS NOr A JMP INSTRUCTION

IS AvE sELECTION
'RETURN

Digital-7-22A-I/O
Page 11

IPoSITrON OF UNIT 7
IPnStTYON OF UNIT .0
IINTF:RLOCI( L~OP, HANGS UP MAIN PROGRAM UNTIL GO~0
IUcqED ~ORMMSUM
'"
LEM
IL~AVE EXTEND MODE
MMRS
IG~T STATUS
AND (4~0QJ)
IC~ECK GO BIT
SZA
INOT GOING?
JMP ."3
IWAIT
JMP I MMITLK
ISvSTEM AVAILABLE

MMITlK,

I~OOP TO ADD ROLL CON~TANT TO CURRENT ADORESS
MMROLL,
r2I
IU~ED AS WORK AREA, MMSBK
LAC MMWA3
ILAST SEAROH OOMMAND

AND (2GO

ISAVE olREOTloN BIT

SZA

IGnING FORWARD

LAM .. 5
ADO ( :3 )

TAD

MMWA1

ITn CREATE LAM .2
IRnLL OONSTANT
lAnD CURRENT cOCATloN
ISTORE CURRENT LOr-ATION

MMwA1
OAC
JMP t MMROI.L
ICOMMON ROUTTN~ ,OR PICKTNG UP CONST!NTS AND SEARCHING

IPI~K

MMCHK,

PARAM£TF.Rs
Q!

'J(CT I MMWA
AND (,'71)

IBLOCK NUMBER

['lAC MM8L'<M

ISAVE ~LOOK NUMBER
It~DEX POYNTER TO ERROR RETURN
IE~ROR RETURN

IS! MMWA
LAC r MMWA

OAC MMERRX
ISl MMWA
LAC I MMltJA

AND (,,000Q1)

OAC
RCl
RTl

MMr.H~1""

RTL
RTL

ADO (MMWAX.1)
OAC MMWA1

I I M SEA RCH ,E X r T

IIMDEX POINTER TO UNIT
IU~11 T
IKP-'EP uNIT ONLY
lIN CALLING SrQuENCE
ICj'EAR ANO ROTATE LINK
IPIIT U~IIT NUMBER IN L..o,PoSITION

IAnDREss OP POSITION POINTEH
lr:nR

TSZ MMWA

LAC I MM\Io1A

ANn (71717)

OAC MMAODR
ISZ MMWA

lions UNIT

IINDEX POrNTER TO STARTING ADDRESS
ISTARTYNG-ADD~ESS
11~ BIT ADDREsS

ILnCATrON POINTER
IINDEX POINTER TO ENDING-ADDRESS

ICAU'lULATE NuMBER OF' DATA AND FILLER WaRns
LAC J MtvlwA
IFINAL. AOnRE9s

ANn (,'77,)

/t~

81T ADDREsS

CMA

ADD

M~1AUDR

SMA
JMP MMSCH5
OAC MMWDC

ISTARTING ADDRESS
III LEGAL
I "'~'O. OF

F-'ORMAT
DATA WQRnS.,

Disital-7-22A-I!O
Page 12

ILnW ORDER 8 elTS
IMAKE NUMBER NEGATIVE

AND (377)
VOR (777400)

TAn (377)
CMA

DAe MM2C~

I~~O

DAC MMFILC

IS,CTION OOUNTER

LAC MM .. ~LKM

"lei OOK

LAM -,

,CALCULATE T~~ DtRECTION TO SEARCH

0' F!LLtR WORDS.,

DESIRED

SI'JA

MMCi( , ,

JMP

MMSC~5

CMA,
ADD

t MMI'jA1

1810CK 0, FORMAT ERROR
ICuRRE~!T

JMP

~OSlTION

HIG H~ R T~ AND e: SIR E1) BL0 CIe
AND TRANSFER DATA FORwARD
~OTSTA~CE TO START BLOCK
I-NUM8€R of DATA WORDS.,
INUMBEQ 0, DATA woROS!I!I1
IKPE~ NUMBER 0' BLOCKS.1
I D, V,I D£ 8 V 400 0 eTA L
I CI) RREN T P,O SIT rON

SPA
MM~F

IS~ARC~

OAe MMWA5

lAr MM .. ~OC
CM~vC:LL

ANn (717 4 00)

RT ~
RTR
RTR

RTR
ADn ~~MqLI(M
OAC

ISTARTING BLOCK
ILAST BLOeK

MMWA7

eMA

ADD

ICIIRRE~IT

MMl~A 1

qMA
JMP MMGH2

Mt'>1C-< "

wrTHTN TRANSFER sECTrON
AND TRANSFER DATA!N REVERSE
IDySTANCE TO sTA~T BLOOK
./START IN REVERSE. TRANSFER DATA FnRwARD
ISTART FWo, TRANS~ER DATA IN REVERSE

,/S~ARC~

ADD MMIAIA15
SM~

JMP
/STA~T

REvERS~,

M~lGH

TRANS~ER

LAw MlI'1SFR

pOSITION

ICIIR.REt\IT ~OSITION Is

DATA FORwARD

SKP
ISTA~~

A~O

TqANSFER DATA FORWARD
LAW MMSCH0
CAe

MMWA~

IS~T

S~ARCH

EN~RANCE

LAC (1)

nAC MMDK

LAC (DAO I MMAODR)

-/FnR IMCRe:MENTING AODRESS
IS!T READ ROUTINE

OAC MMRD;~
ISTA~T SEARC~
MMC~K'j

LA~

(LAC I MMADDR)

DAr.

MMW~3+1

JMP I MM0A5
9!

IS~T ~RIT[

ROuTIN~

IT~ SEARCH
IUNIT AND WORK

AR~A

MMWA2

Digital-7-22A-I/O
Page 13

ISTART

~ORWARU,

MMG~.

TRANRFER DATA IN REV~RSE

LAW MMSRF
SKP

,START AND TRANSFER DATA IN REVERSE
MMGR2,
LAW MMSCHR
OAC MMI,JA5

LAM
OAC MMDI'ii
LA("! MM2CN
SZAVCMA

ADO (1)

ITn DEcREMENT AOD~ESS
IF'TLL.ER COUNTJ::R
I+~ IF THERE ARE NO FILLERS

OAC MMADDR

IEMOING ADDRE~S
IDATA LOCATION POyNTER

LAC MHWA?

IS~ARCH

ADD I

MMl~A

[lAC MM~L.K~1
LAC MM2QN

FOR LAST eLOCK

SNA

JMP

MHr;R~

MMWA6
LAC MMWUC

nAt;

INr'l FILLERS

IEvCHANGE MMWnC AND MM2CN

DAC MM2CI\1

LAC MMwA6
nAC MMWDC
LAC

(NOP)

nAC MMPD3
IFnR FtLL[RS TN ~o ROUTINE
LAC MMW2 ,FOR FILLERS IN wRtT£ ROUTINE, CLA
~JMP MMCHK 1 ~ 1
tSl MMF'lLC
JMP MMGF2
IUEC'TAPE SU8ROUTINE~ READ PDP-'
IFORMAT
JMS MMRuS
I
LAw 8
IO~ LAC (8), BLOCK NUMBER
I
JMP )(
IE~ROR RETURN
I
ZZ0000
IU"IT SELE:CTlnN
01
11~-BIT CoRE STARTING ADDRESS
I
r.2
11~-BIT CORE ~NDtNG ADDRESS, INCLUSIVE
I
MULTI-PROGRAM RETURN

MMRDS,

til

•./MS MM r TLK
LAC MMROS

IC~ECK

DAC MMI,./A

ISTORE POrNTER TO ARGUMENTS
IG~T ARGUMENT~ ANn sEARCH

JMS MMCHK

wITH ~LOCK FOUND
LAW MMRU1
IS,T UP

IP SYSTEM rS

IRETURN PROM

S£ARC~

MMR00,

DAC f"iME:RR
LAi.J MMRU4
ITAC MM8LF
XCT MMWA3

IS'ARC~

ADn (,)

IM~KE ~EAD

MMLC
LAw MMRU1A
DAe MMOATA
nZM MMDONE
DISMIS

INTERRU~T

COMM4ND

COMMANn

FR~E

RETURNS

,Di9itol~7"'22A-,J/o
, Page 14

MMRD',

LAI,.J

IE~ROR FL~G

4Q)0!

DUR1NG REAbING

JMP MMEH)t2

MMRD
CAe MMSUM

REVERSE CHEcKSUM

IR~AD

LAW MMRD2

CAe MMOATA
nISMtS 1
MMRD

EEM

MM"AOOR'~' '

DAr.

LEM
JMS

~1MRU6

IS?' MM .. FtLC

~'MP MM~O'~,'

LAC (f\io'P,<
-MMRI)4,

OAC MMRD3
OISMtS
MMRO

IREAD DATA

, 1 E'" A8 L I=.: E ~ TEN ne: D MEMO RV
IOQ NO'P
IDTSAaLE EXTENDED MEMORy

ICALCULATe: CHECKSUM
Is~CTI'nN

IS~~
ID~

OOUNTER

UP FoR S~CTrnN

NOT STORE REMAINDER
AS OONSTANT

IUqED

IR~AD

~ORWARD

OF SLOCK

CHEcKSUM

ADn MMSUM
SAn 'MMSCIoIS .. l
,JMP ,+3

LAW
JMP

~00

MM~AX2

ISUM CIoIECI< READING

\JM~ MMQLC
,JM? MMRO!71

IC~ECK NExT BLOCK
IR~AO t\IEXT BLnCx

LAC

12'tDS~CTt ON

cOUNTER'

INn FILLERS
IS~T Up WoRD

~OUNTE~

M'M .. 20N

NUMB£R

SNA

JMP MMRD3A
OAr MMWUC
LAr. (Ole I MMADDR)
~An 1'-1MRD3
,JMp MMRD3S .. '
.. IMP MMRD,~8

CHECK:oUM

M~RO~.,

I ADD

lSTORE Nap
lSTORE DAO I N~TRUeT ION

AND I NCR t:MEN T- 'OR 'DEI"!REM ENT ADDRESS
IO~EDAS

~ORK

AREA' MMWA5

ADn MMSUM

IPQEVlnUSCALoULAT16~

DAr

ISTORE NEw RE~ULT
ICIIRRE"JT AODRE'SS
1+1 OR -,

MM~UM

LAr. MMAOOR
TAn MM11K'

OAr

MMAUO~

IN~W

AnDR~SS

J 51:, 'MMI.' DC

I wnR 0

JMP t MMRD6

IC~ECK

nISMIS

LA\,.J MMQLC2
OAf'! ~MnAT,A
'leeT MM\.IA:3

cOUNTER
FOR FILLERS ETC.

IUqED AS wORK AREA- MMSFK
IS~T

DATA FLAG RETURN
COMMANO

IS~ARC,",

M~1L C

nISj~ts

LAf'! t ~MWA1
TAD MM .. DK

I CIIRREN T aLO CK NUMB'ER
1+. OR -1

nAc I

IN~W

MMRO

MM~vA 1

BLOCK NUM8ER

Digital-7-22A-I/O
Page 15

SAn t

Ml"lWA 1

ICnMPARE TO CORRECT NUMBER

.JMP • +3
l,.A\4 700
,.1 M~ MMf: R)( 2

18LOCt( MARK ERROR

LAC

IsrCTlnN COUNTER

MM~lL.C

SZA
J M,P I MM8 L r.

IR~TURN FOR Nr.~T eLOCK
ISTOP THE TAPE:
lAnD ROLL CONSTANT

'MMLC
,JMS MMROLL

CLe
DAr.: MMDONg.
IUEC.T~PE

IFORMAT
I
I
I
I
I
I

DI~MIS

WRyTE SUBROUTINE,

IS~T

pop-,

JMS MMWHS
LAW B
JMP X

lOR LAC (8), BLOCK NUMBER
1e:~ROR RETURN
I U~I ITS ELe: CT I (') N
11~-8IT CORE STARTING

2Z0fOPJ0
C1

C2
MUtT! "pRr)(~RAM

DONE SWITOH

RETURN

ADDRE~S

11~-BIT

ENDING AOnRe:SS,INCLUSIVE

IC~ECK

IF SYSTEM

t2!

,-JMS
.JM~

IRETURN

MMWR1,

MM I TLK
MMCHK

FREE

IPTCK uP ARGUMENT!=; AND SEARCH

~ROM Se:ARC~

wITH dLOCK FnUND
LAW MMWR2
ISrT UP INTERRUPT RETURNS
DAC MMERR
LA!"} t-1MwR4
DAC MM~LF'
LAW MMWR3
DAe MMDATA
nZM MHOONe:
OLe
DAC MMSUM
ISTART CHrCKSUM
XCT MMWAJ
ISpARC~ COMMAND
ADD (2,
IC~EAT£ WRITE COMMAND
MMLC

MMWR?,

DISMtS
LAW 600

IE~ROR

FLAG DURING WRITING

,}MP MMERX~
MMWR~,

EEM

IE~A8LE

LAC t MMAODH

IO~

ExTENnED MODE

LEM

IDTSABLE EXTEND MoDE

CLA

~MwR

MMWR~8,

JMS MMRD6
rSl MMFILc
JMP MMWH~
LAC MMW2
nAC M~wR3+1

MMWR4,

LAC MMSlJM

MMWR'A,

ICALCULATE CHEOKsuM
ISrcTI"N COUNT~R
ISrT UP FOR 2ND S£CTION
ICI A

nI~Mts

IW~ITE

CHE:CKSUM

CMi\

MMWR
JM~
JM~

MMRLC

MMWA,

IcwECK NExT SlOCK NUMBER

Di Si tal-7~22A-I!O
Page 16

LAC ·MM2CI\I
SNA
JMP

MMW~3A

DAC MMWJ)C
LAC (LAC I MMADDR)
MMWH3+,
JMP MMWHJ8",t
JMP MMWRJ8

SAD

MMWA~=M~SAVE
MMWAC;=M~R06
MMWA~,M~RDS

~~MSF'K=Mr.1AL.C

MMWA?=MMCHK1.'
MMS8K=M~ROLL.

MMWA=MMWRS
MMSUM=M~tTLK

MMwA1.M'1SUM
MMRS A• MM~-R R
SlA~T

11.

DIAGRAMS

11. 1

Flow Cha~ts

FROM THIS POINT ALL ITEMS ARE DONE IN
THE INTERRUPT SERVICE ROUTINES WHICH
ARE OVERLAPPED WITH THE RUNNING OF
THE MAIN PROGRAtot.

Gross DECtape Subroutine

Digital-7-22A-I/O
Page 17

Read Routine

Di 9ito 1-7-22A -1/0
Page 18

MMRD3

SWITCH I
MMRD2

READ WORD.
TURN ON
EXTEND MODE

Read Routine (continued)

Di gi ta 1-7-22A -1/ 0
Page 19

PICK UP ERROR
CODE 711l11l

STOP TAPE.
SET DONE
INDICATOR

Read Routine {continued}

Di gital-7-22A-I/O
Page 20

PICK UP

ERROR CODE 7(11(11

Write Routine

Di gi ta 1-7- 22A-1/ 0
Page 21

PICK UP ERROR
CODE 6'"

SAVE
DECTAPE STATUS

MMWR3+1

~
LOAD CORRECT
WORD
FROM MEMORY

Write Routine (continued)

STOP TAPE.
SET DONE
INDICATOR

Digital-7-22A-I/O
Page 22

MMCHK

CALCULATE LAST
BLOCK AND SAVE

SET TO ENTER
SEARCH ROUTINE TO

...-----1 START IN REVERSE
BUT TRANSFER
FORWARD (MMSFR)

Common Routi ne to Pi ck Up Parameters
and Initiate Searching

Di gi ta 1-7-22A -1/ 0
Page 23

EXCHANGE DATA
WORD COUNT WITH
FILLER WORD COUNT

SET SWITCH I
IN READ ROUTINE
TO NOP

Common Routine to Pick Up Parameters
and Initiate Searching {continued}

Digi ta 1-7-22A -I/O
Page 24

SEARCH FORWARD
TRANSFER IN REVERSE

SEARCH AND TRANSFER
IN REVERSE

MMSH5
PICK UP
ERROR CODE 100

Search Routine

SEARCH IN REVERSE
TRANSFER FORWARD

SEACH AND TRANSFER
FORWARD

Di gi ta 1-7-22A -1/0
Page 25

PICK UP
ERROR CODE 30'"

ENABLE API
ENABLE CHANNEL

YES

SET SWITCH 3
TO CONTINUE IN
REVERSE DIRECTION

ADD SEARCH
- - -__

~~:~~~TgO:~~~~~ ......--~

AND SAVE AT MMWA

L..._ _--._ _ _- '

Search Routine (continued)