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DEC-12-SI1B-D

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PDP-12

LIBRARY

LINC-8 SIMULATOR TRAP PROCESSOR

Order DEC-12-SI1B-D from Program Library, Digital Equipment
Corporation, Maynard, Massachusetts 01754

Price $1.00

Direct comments concerning this document to:

Software nformation Service
I

Digital Equipment Corporation

Maynard, Massachusetts 01754

CONTENTS
Pag
1.

Abstract

Equipment and Storage Requirements

2.1

Equipment

2.2

Storage

Loading, Starting and Restarting

2
2

3.1

Loading Procedure

3.2

Normal Starting Procedure (Start 400)

3.3

Starting Procedure for Immediate GUIDE or

2
2

LAP6-3L

Loading and Starting (Start 20)

3.4

The Instruction

Trap Enable Flip-Flop

3.5

Normal Restart

(Start 400)

3.6

"User 20" Restart (Start 20)

3.7

GUIDE Load Restart (Start 700-717)

Program Operatlpn

4.1

Illegal Teletype Characters

4.2

Undefined Instruction Error Stop

Internal Operation

3
3

4
5
5

5.1

Overview

5.2

Console Starts and Restarts

5.3

Operation of the Instruction Trap Hardware

5.4

Machine State Saving

5.5

Instruction Identification

5.6

TYP Processing

5.7

KBD Processing

5.8

Return To User Program

6
7
7

7
7
8

LI NC-8, Simulator

6.1

Adaption To Process Additional

6.2

Example: Operating the XY12 Plotter Control with LINC
or

6.3

NC-8 OPR's

LINC-8 OPR's

Adaption for Convenient Trap Processor Loading from
or

6.4

Trap Processor Adaptions

GUIDE

LAP6-3L Tapes

Adaption for Convenient Loading With a User Program From
a

DIAL Tape

iii

CONTENTS (Cont)
Adaption for Loading of Programs Other Than GUIDE and LAP6-3L
By The Trap Processor
Adaption to Suppress Teletype Character Echoing
Assembly

Listing

ABSTRACT

The LINC-8 Simulator Trap Processor handles Teletype input and output for LINC-8 and classic LINC
programs when they are run on the PDP-]2.

must be loaded into the PDP-12 core memory with any

LINC-8 or classic LINC program which uses the keyboard, or any classic LINC program which uses the
Teleprinter, in order for that program to run on the PDP-12.

The trap processor operates by using the PDP-12 Instruction Trap Facility to detect execution of either
of the two LINC-8 Teletype input/output instructions by the user's program

responds to user's

execution of a Teletype instruction by executing coding to simulate the instruction's LINC-8 or classic

LINC effect.

After simulation of the instruction, the trap processor returns control to the user program

Users may easily adapt the LINC-8 Simulator Trap Processor to their own purposes.

Explicit instruc-

tions for a number of useful adaptions are provided in this document, along with enough information on

the internal operation of the program to permit users to easily implement adaptions of their own invention.
It is

In this

connection, attention is directed to the Dispatch Table Trap Processor, DEC-12-SI2A.

a more suitable starting point for building extended trap processors which process a large number

of different trapped instructions than is the LINC-8 Simulator Trap Processor.

An important limitation of the trap processor is that it is not interruptible.

may not be operated

when the PDP-12 Program Interrupt is enabled.
This document applies to the machine readable program version bearing software product code

DEC-12-SI1B-UA.

2. 1

EQUIPMENT AND STORAGE REQUIREMENTS

Equipment

The LINC-8 Simulator Trap Processor is at present distributed in LINCtape form only, and therefore
requires a

PDP-12 with LINCtape control and at least one TU55 DECtape/LINCtape transport for

program loading.

The program itself will run on a minimum PDP-12.

The program operates correctly both in 4K PDP-12's and in PDP-12's having any amount of extended

memory up to the 32K maximum total

Instruction traps originating in extended memory will be pro-

cessed no differently than the same instruction traps originating in basic memory.

2 2
.

Storage

The program occupies most of the locations below 462, plus locations 700 to 717, all in PDP-1 2 memory
segment 0.

3. 1

LOADING, STARTING AND RESTARTING

Loading Procedure

The program is distributed on a DIAL tape

Load and start that copy of DIAL , and type into DIAL,

ILO L8SlM,0i

(The symbol

means Teletype LINE FEED.

}

means CARRIAGE RETURN.)

The LINC-8 Simulator Trap Processor will be loaded from the DIAL tape into the PDP-1 2 core memory,
and the computer will halt.

Normal Starting Procedure (Start 400)

3.2

Press I/O Preset,

and then Start 400.

The program will turn on the Instruction Trap Enable Flip-Flop

and halt with the Instruction Field set to 2 and the Data Field set to 3.
Trap Enable Flip-Flop is on by observing the console TRAP indicator.
it is

This indicator should be lit.

The error may be either a machine error or an operator

not, some kind of error has occurred .

error.

Verify that the Instruction

Reload the trap processor and try again

Now read in the user program.

the program is located on some specific block(s) of a LINCtape,

mount the tape on either transport and execute an appropriate tape instruction from the console as if
the machine were a LINC or a LINC-8.

the user program is a named file on a LAP6-3L or GUIDE

tape, mount the tape on unit 0, set the LOCAL -OFF-REMOTE switch to REMOTE and press CONT.

guide or LAP6-3L* will be loaded, and the user program may be recalled using the usual GUIDE or
LAP6 program loading procedure.

If the

user program is on paper tape, read it in and start it using the usual paper tape loading and

starting procedures, as described in the Binary Loader operating instructions,

DEC-08-LBAA-D.

*LINC-8 and LINC users will recall that the GUIDE program starting procedure may be used with
either GUIDE or LAP6-3L.

Switch the processor mode to the PDP-8 mode by executing the PDP instruction (octal: 0002) before

Mode changing through use of I/O Preset in conjunction with the console

using the Binary Loader.

Mode key should be avoided because I/O Preset clears the Instruction Trap Enable Flip-Flop.

3.3

Starting Procedure for Immediate GUIDE or LAP6-3L Loading and Starting (Start 20)

To automatical ly load and start a LINC-8 GUIDE or LAP6-3L tape along with the trap processor, load
the trap processor from the DIAL tape as directed above, and then press I/O Preset, Start 20, rather

than I/O Preset, Start 400.

A GUIDE or LAP6-3L system will be read in from unit 0 and started

This procedure duplicates the "Start 400" procedure given above, with the exception that the computer

does not halt between the trap processor initialization and the loading and starting of the GUIDE or

LAP6-3L system

3.4

The Instruction Trap Enable Flip-Flop

Once a user program has been read in and started , the machine behaves like a LINC-8 or classic
LINC with respect to Teletype input and output thereafter, but only if the Instruction Trap Enable
Flip-Flop has been set.

The PDP-12 Instruction Trap Enable Flip-Flop must be set in order for the

trap processor to work.

The state of this flip-flop is indicated by the TRAP light on the computer

console.

the trap processor is loaded exactly as directed above, and If the user program is operated

exactly as its instructions direct, the Trap Enable Flip-Flop will never be cleared, and will cause no

However, in practice it is sometimes cleared (by the operator pressing I/O PRESET for

problems.

example), so some convenient methods for resetting it are included in the trap processor program in the
form of the fol lowing restart procedures.

3.5
If

Normal Restart (Start 400)

the Instruction Trap Enable Flip-Flop has been cleared,

may be set again (providing the trap

processor has been loaded into core as directed above) by starting at location 400 in memory segment 0
(absolute address 00400)
Field (IF)
Set

Note that the START 400 key may not be used for this unless the Instruction

set to 0 because

START 400 takes the high order 5 bits of the starting address from the IF

0400 into the Left Switches and use START LS, rather than Start 400.

the Trap Enable Flip-Flop and halts the computer.

firmed by observing the console TRAP indicator.)

Use of this entry point sets

(Setting of the Trap Enable Flip-Flop may be conPressing continue after the computer has halted

causes a transfer to location 400 in memory segment 2 (absolute address 04400), with the Data Field
set to 3.

3.6

"User 20" Restart (Start 20)

Starting at location 20 in memory segment 0 (00020) sets the Trap Enable Flip-Flop and immediately
transfers control to location

20 in memory bank 2 (absolute address 04020), with the Data Field set to

Note that the START 20 key may not be used for this unless the Instruction Field (IF) is set to 0

because START 20 takes the high order 5 bits of the 15 bit starting address from the IF.
Left Switches and use Start LS, rather than using

3.7

Set 0020 in the

START 20,

GUIDE Load Restart (Start 700-717)

A third alternative is to start at any location between 700 and 71 7 in field 0.

Use of any of these

entry points sets the Trap Enable Flip-Flop and then loads and starts the LINC GUIDE or LAP6 system
(if

an appropriate tape is mounted on transport 0 and the LOCAL-OFF-REMOTE switch is set to

REMOTE),

PROGRAM OPERATION

Once the LINC-8 or classic LINC user program and the LINC-8 Simulator Trap Processor have both
been loaded into PDP-12 memory, the operating instructions for the user program apply, and the user
program will behave as it would on a LINC-8 or classic LINC, and no special account need be taken
of the fact that a

PDP-12 rather than a LINC-8 or classic LINC is being used.

minor exceptions to this.

The PDP-12 console operates slightly differently from the LINC-8 console

and the classic LINC console

Also, the characters which in the LINC are obtained by striking the

CASE key and then some other key such as
Teletype key.

There are a couple of

and Bare obtained in the PDP-12 by striking a single

The Teletype keys which are used to obtain the various LINC codes are indicated in

the fo lowing diagram of the Teletype keyboard
I

Figure

Location of LINC keys on the Teletype keyboard

An additional exception to strict classic LINC compatibility concerns "echoing" of keyboard characters
Characters typed into a user program running with the trap processor are automatically printed on the
Teleprinter by the trap processor.

Instructions for suppressing this feature are given in Section 6.6,

Adaption to Suppress Teletype Character Echoing.

Illegal Teletype Characters

Some teletype keys, such as the semi-colon key, are not used for any LINC characters, either standard
or special .

These keys should not be struck when the trap processor is being used to run LINC or

LINC-8 programs.
up arrow, "t".

one of these

Control

legal keys

struck,

printed on the Teletype preceded by an

not returned to the user's LINC-8 or classic LINC program until a legal

character is struck

The fol lowing Teletype keyboard characters are illegal:

4.2

TAB,

@, ], t,

<, >.

Undefined Instruction Error Stop

The trap processor halts at location 130 in memory segment 0 when any instruction other than a Teletype
input or output instruction is given

address of the instruction

The trapped instruction is contained in the accumulator, and the

location 134 of memory segment 0.

INTERNAL OPERATION

Overview

Teletype input-output in LINC and LINC-8 programs involves only three instructions:

Keyboard

(mnemonic KBD; instruction code 515), Type Out (mnemonic TYP; instruction code 514) and Key Struck

(mnemonic KST; instruction code 415).

These are the only LI NC-8 nstructions whose operation

involves the LINC-8 Simulator Trap Processor.

The processing performed by the LINC-8 Simulator

Trap Processor for the KBD and TYP instructions consists of detection of their execution by the user
program, and execution of programming to reproduce in detail their LINC-8 or classic LINC effect.

The KST instruction is a skip instruction which skips when the Teletype keyboard flag is set.
is

set by the hardware when the operator strikes a Teletype key.

no keyboard character available for the user program to read in.

This flag

The trap processor clears it when there

Processing for the trapped instructions KBD and TYP consists of three steps

The first step consists of the identification of the instruction

the occurrence of an instruction trap.

causing the trap.

Processing is initiated by

The second step is the execution of programming to simulate the LINC-8 effect of

the particular trapped instruction.

The final step is the return of control to the user program.

In addition to the "trap processor proper",

which performs as described above, the program as distrib-

uted contains small amounts of code to implement the various console restarts described above.

5.2

Console Starts and Restarts

The program is initial ly loaded into memory segment 2, and relocates itself into segment 0 as soon as
it

started.

This technique

used because it leads to a particularly simple procedure for loading the

program directly from LINCtape using the console functions
ient Load ng of the Trap Processor from
i

See Section 6.3, Adaption for Conven-

GUIDE and LAP6-3 L Tapes

for a description of this

the routine had to be loaded Into segment 0 directly, the console procedure for loading

procedure

would be more

complicated than it is because the operator would have to set one of the 5-bit Field Registers to 0 before
execution of the tape read instruction in order to load data into segment 0

As is , the user may initial ly

load the program into any memory segment for which memory is physically present

Both the "Start 20" and "Start 400" program starting procedures execute the trap processor relocator
routine at symbolic location SETUP.
tion field into memory segment 0.

used only once.

with

This routine relocates the trap processor from the current instruc-

Notice that the relocator routine is not itself relocated, since it is

After the trap processor has been relocated, the locations 700 through 717 are fil led

"JMP GUIDE".

This operation provides for restarting of the GUIDE system using the Start Left

Switches function when any tape instruction is set into the Left Switches.

5.3

Operation of the Instruction Trap Hardware

The trap processor operates with the Instruction Trap facility enabled, so execution of any trappable
instruction (except tape instructions) by the user's program causes a transfer of control to location 141
in

memory segment 0 (absolute address 00141 ).

instruction following the trap instruction

Also, the low order 12 bits of the address of the

stored in location 140, and the contents of the Instruction

Field and Data Field when the trap occurred is stored in the Save Field Register.

5.4

Machine State Saving
The instructions between 140 and symbolic location FETCH saves registers and indicators whose contents
will be affected by the operation of the trap processor.

to the user program .

They will be restored before control is returned

Notice that the Overflow flip-flop and memory location 0 are both saved

They

5.5

are both affected by the operations in the trap processor

Instruction Identification

5.6
The code from symbol ic location FETCH to OP14 obtains the instruction causing the trap and transfers
control to the subroutine which performs the

LINC-8 function of the particular instruction.

TYP Processing
5.7
TYP and TYP I (OPR14 and OPR I 14) are processed identically, by the subroutine beginning at OPII4.

Note that exit from the subroutine does not occur until the Teleprinter has completely finished printing
the character.

This assures that the printer will be ready to accept a new character the next time the

subroutine is entered.

KBD Processing
The routine begins at tag OP15 and ends just before tag INIT.

has three functions.

are interrelated and are not performed in any simple sequence by the routine.

The functions

Consequently, the

following discussions of them do not reference specific pieces of code within the routine.

The first function performed is the translation of ASCII character code characters into LINC character

code characters.
in

(Part of the definition of the

LINC KBD instruction is that characters which are read

by the instruction have the LINC character code.) This translation sometimes requires that two

characters be passed to the user program when only one Teletype character has been typed

LINC "special " characters (?, =, u,

, ,

Some

did not have their own keys, and existed only

by virtue of the convention that the "CASE" character followed by some other character was to be
interpreted as a "special" character.

The Teletype keyboard has a "SHIFT" facility whereby a single

key may generate more than one character code, and, because of its ease of use, this "SHIFT" technique rather than the "CASE key" technique is used in the PDP-12 (and also the LINC-8) to generate
the "special " characters .

But since LINC programs "expect" to have special characters entered as two

characters, and in general have no provision for accepting them in any other way, the trap processor

must generate the appropriate pair of characters in response to the use of a single Teletype key.

The second function of this routine is the interpretation of the I bit.

when raised, means,

This bit,

"Don't execute the next instruction until a character from the keyboard has been acquired
character has been typed , pause until the user types one

If no

"
.

The final function of the routine is the clearing of the keyboard flag
by the LINC KST instruction

This

the flag which is sensed

Note that when two LINC characters are generated in response to one

Teletype character, the flag is not cleared until after the second LINC character has been generated.
This assures that the user program will "think " that the operator has struck the second character, and

execute the KBD instruction which col lects that second character.

5.8

Return to User Program

The routine to return control to the user program begins at symbolic location RET and ends at OVN
The routine is entirely straightforward

values prior to entry to the trap processor.

1
1

simply restores the various registers in the machine to their

Note that when the KBD instruction has been given the AC

get fi lied with some character code rather than with its contents at the time of trap processor

entry.

LINC-8 SIMULATOR TRAP PROCESSOR ADAPTIONS

6.1

Adaption to Process Additional LINC-8 OPR's

LINC-8 and classic LINC instai lations often use instructions of the LINC OPR group for purposes other
than control of the Teletype.

For example, an installation

controlling pen motion on an incremental plotter.

one of six directions.

In this section,

may use OPR's 5, 6, 7,

10,

1 1

and 12 for

Each OPR causes the pen to move one increment in

we indicate how the LINC-8 Simulator Trap Processor may be

"custom tailored" to process additional OPR's or other trapped instructions.

general , such modifica-

tions involve three steps:

extension of the trapped instruction identification routine to recognize trapped instructions

other than the Teletype OPR's
b.

addition of a routine to simulate the effect of the LINC-8 or LINC OPR instruction; and

return of control to the user program

The extension to the trap identification routine consists simply of adding instructions to transfer control
to a subroutine when one of the new OPR's

recognized.

The new instructions should be added at

symbolic location OTHERS, and care should be taken to preserve the error stop which occurs when the
trapped instruction is not recognized.

A routine which is entered when the new OPR's are given must be added to the program

The details

of this routine are entirely dependent on the character of the new OPR.

Finally, the user program must be re-entered .

This

accomplished by transferring control to symbolic

location RET.

Existing coding attends to the details of restarting the user program

6.2

Operating the XY12 Plotter Control with LINC or LINC-8 OPR's

Example:

Suppose that a LINC-8 or LINC user is operating an incremental p lotter with 6 OPR instructions which

work as follows:

OPR
OPR
OPR
OPR
OPR
OPR

5 (0505)

- lower pen
- raise pen

6 (0506)
7 (0507)
10 (0510)

- move drum up

- move drum down

11 (0511)

- move pen right

unit

12 (0512)

- move pen left

unit

Suppose further that each OPR "pauses" until the completion of the plotter operation caused by its
execution

That is, execution of an OPR is not completed, and execution of the fol lowing instruction

does not begin unti

the plotter operation caused by the OPR is completed

This "paused" mode of

operation obtains whether or not the instruction's I bit is set.

he XY12 plotter control used the fol lowing PDP-8 mode commands:

PLSF

(6501)

- Skip on Plotter Flag

PLCF
PLPU

(6502)

- Clear Plotter Flag

(6504)

- Pen Up

PLPR

(6511)

- Pen Right

PLDU
PLDD

(6512)

(6514)

PL PL

(6521)

- Pen Left

(6524)

- Pen

PL PD

Drum Up
Drum Down

Down

The plotter flag is set by the completion of a plotter command affecting the pen or the drum.
cleared by the PLCF command only.

The pen and drum commands do not affect the plotter flag.

The following modifications to the LINC-8 Simulator Trap Processor will enable it to run LINC or

LINC-8 programs which operate the plotter in the manner described above:

Replace the instruction at symbolic location OTHER with the following instruction:

OTHERS

JMP PLOT

Add this subroutine to the program just after symbolic location ENDX.

(Actually, the

routine could be inserted anywhere before TABE, which is the last location loaded into memory

segment 0 by the loading sequence

/SUBR TO RUM XY12 CONTROL FROM LINC
/MODE USING TRAPPED GPRS.
/SAVE
STA I
PLOT,
0
PL INST,

BCL

INSTRUCTION

/IGNORE INSTRUCT KTM

BIT

ADA I
-OPRAPO I
JMP PLERR
ADA
1

/OPR 12 OR LESS?
ERROR
/NO.
/YES. OK SO FAR

APO
JMP PLERR

PLGO,

ADA I
ADD PLTAB-1
STC .+1
HLT
PLGO
STC
PDP
PMODE
PLCF
HLT
PLSF
JMP .-1
LINC
LMODE
JMP RET

/OPR 5 OR MORE?
ERROR
/NO.
/YES. OBTAIN COMMAND

/BECOMES ADD PLTAB

/PLPU, PLPR, ETC

/RETURN TO USER

/INSTRUCTION NOT RECOGNIZED
PLERR,
LDA
PLINST
JMP ERR
PDP
PMODE
PLTAB,
PLPD
PLPU
PLDU
PLDD
PLPR
PLPL
LINC
LMODE

/DO ERROR STOP

/PEN DOWN. OPR
/PEN UP
/DRUM DOWN
/DRUM UP
/PEN RIGHT
/PEN LEFT .OPR

These modifications are most easily made by modifying the program's source and reassembling the program, as opposed to manual ly inserting the new instructions from the computer console.

6.3

Adaption for Convenient Loading of the Trap Processor from a GUIDE or LAP6-3L Tape

A particularly convenient way of using the trap processor with an existing GUIDE or LAP6-3L tape is
to copy the program in exactly its present form onto some otherwise unused tape blocks and subsequently

load it directly from these tape blocks using console functions .
is

The advantage of this loading procedure

that it involves only the tape with the programs which are to be run with the trap processor

separate DIAL tape is required for program loading purposes.

Procedures are given below for copying the trap processor onto a GUIDE or LAP6-3L tape and for

subsequently reading it back into core for use with a LINC or LINC-8 program
is

Note that the program

stored in pairs of blocks which begin at blocks having block numbers which are multiples of 10 - e.g.,

blocks 10 and

1 1 ,

or 230 and 231

This

done so that the tape group instructions WCG and RCG may

be used to effect the tape operations involving the programs

Notice also that this procedure may be used with LINCtapes other than GUIDE or LAP6-3L tapes

Procedure to Copy the Trap Processor onto a GUIDE or LAP6-3L Tape:

Load the T rap Processor from a DIAL tape using the usual procedure.

Press I/O Preset

Mount a GUIDE or LAP6-3L tape on unit 0.

Set in the Left and Right Switches:
Left

Right

0705

IXXO

(XX 0 is the first tape block of the pair of blocks in which the program is to be stored
5.

Press

DO. The Trap Processor will be written into the designated tape block.

Procedure to Load the Trap Processor from a GUIDE or LAP6-3L Tape:

Mount the GUIDE or LAP6-3L tape on unit 0.

Press STOP.

Press I/O Preset

Set in Left and Right Switches:
Left

Right

0701

IXXO

(XX 0 is the first tape block of the pair of blocks onto which the program has been copied
4.

Press DO.

Press Start 20.

The Trap Processor will be read into memory segment 2.

The Trap Processor will relocate itself from segment 2 into segment 0 and

the GUIDE or LAP6-3L System will be loaded and started

6.4

Adaption for Convenient Loading with a User Program from a DIAL Tape

The LINC-8 Simulator Trap Processor is designed to be loaded into memory ahead of user programs.
normal use,

loaded into memory segment 2, and relocates itself into segment 0 as soon as it is

started in order to leave segment 2 free for user programming.

processor so that it may be loaded directly into segment 0.

It is

not difficult to modify the trap

This modification may be made in the

assembly source of the program, and this modified source may be assembled along with a DIAL source
of the user program

Such a source may be obtained from a LAP6 source through use of the program

CO NVERT

program

However, once the program is loaded from LINCtape, one of the trap processor restarts

The resulting program may then be fi led and retrieved from LINCtape as a single binary

must be executed in order to initial ize the trap processor and set the Instruction T rap Enable Flip-Flop.

Production of a source modified for segment 0 loading consists of the fol lowing three steps:

Insert the

pseudo -op SEGMNT 0 before the first line of code in the source program.

Replace the instructions in location 20 and symbol ic location RST400 with

"JMP INIT"

This step prevents entry to the trap processor relocating program
3

Delete all instructions after symbol ic location TABE.

processor relocation routine, which

6.5

It is

These instructions comprise the trap

no longer needed.

Adaption for Loading of Programs Other than GUIDE and LAP6-3L by the Trap Processor

easy to modify the trap processor to load programs other than GUIDE or LAP6-3L when using the

automatic loading and starting feature.
at symbolic location GUIDE+1

GUIDES

The code which implements the load and start feature begins

quite straightforward:

JMP INIT
LDF 2
RDC
7400
LDF 3
LIE 2

/INITIALIZE TRAP PROCESSOR
/READ GUIDE START BLOCK
/INTO QUARTER 3> SEGMENT

D JR

JMP

400

/START GUIDE

As an example, suppose that the trap processor is to be used with a LAP6 version other than LAP6-3L
Suppose the LINC-8 or classic LINC console procedure for loading and starting the other LAP6 version
consists of executing the double-word tape instruction

trap processor will perform this operation

RCG 7300, and then pushing "START 20"

The

the code at symbol ic location GUIDE is replaced by the

fol lowing:

GUIDES

JMP
LDF
LDA
RCG
STA

INIT

/INIT lALIZE TRAP PROCESSOR

/PUT RCG 7300
6 AND 40

/40

201 6

LDA
7300
STA

201 7

LDF
LIF
JMP

2
1

/JUMP TO 40

The instruction RCG 7300 is inserted into locations 16 and 17 in memory bank 2 -

.e.

4016 and

4017 - and is immediately executed from these locations. * The next instruction is taken from location
4020.

6.6

This is the starting location of the program

Adaption to Suppress Teletype Character Echoing

The trap processor echoes characters typed by the computer operator on the console teleprinter in
addition to transmitting them to the user program .

This character "echoing" may be suppressed by

removing seven instructions beginning at symbolic location LOOl

After modification, the section of

the program near LOOl should look like this:

STC
STC

LOO.

AC
UPC

/STORE IT FOR TRANSFER
/CLEAR LEFT OVER BUFFER

RET

/READ CHAR AND
/CLEAR KEYBOARD FLAG
/RETURN TO USER PROGRAM

KRBA
JMP

LOOl .
/

/ILLEGAL CHARACTER
LDA I

RETX,

/PRINT UP ARROW.

*One might ask here, "What happens if the RCG Instruction fails at, say, block 301 ? The computer
will try to execute the

RCG again from the beginning, but the instruction will have been destroyed by

The answer is that when the PDP-12 tape control retries an instrucdoes not read the instruction from core a second time. It uses the same data it obtained when

the arrival in core of block 300. "
tion,

the instruction was read initially.

eiee
§001
0102
0003
i0i4
0005
0016
0017
0010
0011
0012
0013
1014
0015
0016
0017
0020
0021
0022
0023
0024
0025
0026
0027
0030
0031
0032
0033
0034
0035
0036
0037
004i
ii41
0042
0043
0044
0045
0046
0047
0050
i@5i
0052
0053
0054
0055
0056
0057
0060
0061
0062
0063
0064
0065
0066
0067
0070
0071
0072
0073
0074
0075
•

• 20

/LINC-8 simulator trap processor. DEC-12-SI1B

/copyright 1969
/MAYNARD, MASS,

DIGITAL EQUIPMENT CORP

LANGBEIN, 27 MAY 1969
/REVISED 21 JULY 1969
/REVISED 8 AUGUST 1969

/D,

/OPERATION OERNITIONS FOR LINC MODE ASSEMBLY
/OF PDP-8 mode IOT InSTRUCIOnS
KCCA86032
KRSA86034
KRBA«6036
TSFA«6041
TLSA«6046
RMFA«6244
/

/some LINC-8 definitions
OPR»500
KB0«515
/
• 20

0020
0021
0022
0023
0024

JMP
LOF
LIF
OJR
JMP

6463
0643
0602
0006
6020

ST20

/BECOMES JMP INIT

3
2

/GO TO 20 IN SEGMENT
/(04020)

ST400

/BECOMES JMP INIT

0025
0026
0027
0030
0031
0032

6466
0643
0602
0006
0000
6400

/400 restart
RST400, JMP
LOF
LIF
OJR
HLT
JMP

400

/GO TO 400 IN SEGMENT
/ (04400)

0033
0034
0035
0036
0037
0040
0041

6356
0642
0700
7400
0643
0602
7400

/START GUIDE
JMP
GUIDE.
LOF
ROC
7400
LOF
LIF
JMP

INIT
2

/READ GUIDE START BLOCK
/into QUARTER 3, SEGMENT

3
2

1400

/start guide

RET

/UNIDENTIFIED INSTRUCTION
/IN AC AT HLT, RETURNS TO
/USER W AC cleared WHEN
/continue pressed,

0130
0131

0000
6221

/error STOP
• 130
HLT
ERR.
JMP

/MISC CONSTANTS
• 134

0134

0000

PC.

0135
0136

0070
0001

M70.
ONE.

70
1

/address of trapped
/instruction

0076
0077
0100
0101
0102
0103
0104
0105
0106
0107
0110
0111
0112
0113
0114
0115
0116
0117
0120
0121
0122
0123
0124
0125
0126
0127
0130
0131
0132
0133
0134
0135
0136
0137
0140
0141
0142
0143
0144
0145
0146
0147
0150
0151
0152
0153
0154
0155
0156
0157
0160
0161
0162
0163
0164
0165
0166
0167
0170
0171
0172
0173
0174

0141
0142
0143
0144
0145
0146
0147
0150
0151
0152
0153
0154
0155
0156

4242
0261
4225
0005
0241
0455
2136
4232
213 6
0454
0011
4222
0057
0000

/TRAP ENTRY AND MACHINE
*141
STC
AC
rol
1
STC
LC
QAC
ROL
1
QL2
ADD
ONE
STC
Q
ADD ONE
FLO
CLR
STC
OVL
17
SET
I

state saving
/SAVE AC
/SAVE LINK
/GET

11 Q REG BITS

/GET

BIT

/SAVE

/GET OVERFLOW BIT IF ON

/SAVE IT,0=OFF, isON
/SAVE LOCATION 0

0
/

/instruction identification.
0157

0002

4160
4161
4162
4163
4164
4165
4166
4167
4170

6234
0335
1371
3364
7402
7240
1140
3334
1734

FETCH,

4171
4172

6201
6141

COFX,

0173
0174
0175
0176
0177
0200
0201
0202
0203
0204
0205
0206
0207
0210
0211

1460
0515
0467
6250
1460
0535
0467
6250
1460
0534
0467
6212
1460
0514
6130

0212
0213
0214
0215
0216
0217
0220

1000
0242
0500

POP
PMODE
RIB
AND
TAD
DCA
7402
STA
TAD
DCA
TAD

M70
CDFX

/READ INTERRUPT BUFFER
/GET INSTRUCTION FIELD
/MAKE IT INTO A CDF N

.+1

140
PC
I

CDF
LINC

/BECOMES CDF N
/SET AC TO -1
/COMPUTE ADDRESS OF
/trapped INSTRUCTION
/OBTAIN INSTRUCTION
/CAUSING trap
/SET DATA field TO 0

LMODE

OTHERS,

SAE
KBD
SKP
JMP
SAE
KBD
SKP
JMP
SAE
OPR
SKP
JMP
SAE
OPR
JMP

0P14

LDA

/IS

KBD?

DOKBD

/NO
/YES.
/IS IT KBD I?

DOKBD

/NO
/YES.
/OPR

I
I

14?

0P14
I

/NO
/YES
/OPR 14?

ERR

/PUT JMP TO
/CHECKS FOR OTHER
/INSTRUCTIONS HERE,
/OUTPUT, GET CHARACTER

lOB

60 46

tlsa

0500
6041
6216

lOB

/OUTPUT

tsfa
JMP

/CHECK IF DONE
,-2

/RETURN TO USER PROGRAM
0221
0222
0223

1020
0000
2247

RET,

LDA

OVL.,

ADD

OVN

/EXIT TRAP PROCESSOR

/3777 CAUSES OV

0175
0176
0177
0200
0201
0202
0203
0204
0205
0206
0207
0210
0211

0224
0225
0226
0227
0230
0231
0232
0233

1020
0000
0321
0040
0017
1020
0000
0314

0234
0235
0236
0237

0212
0213
0214
0215

02 40

0241
0242
0243

1000
0140
1620
6000
4246
1120
0000
0006

02 16

02 44

05 00

0217
0220
0221
0222
0223
^224
0225
0226
0227

0245
0246
0247

6244
0000
3777

02 30

0231
0232
0233
0234
0235
0236
0237
024 0
0241
0242
0243
0244
0245
0246
0247
0250
0251
0252
0253
0254
0255
0256
0257
0260
0261
0262
0263
0264
0265
0266
0267
0270
0271
0272
0273

LOA
LC,

/GET link

ROR
SET

/RESTORE link
/RESTORE location

LOA
Q*

ROR

LDA
140
BSE
JMP
STC
ADA
AC

/RESTORE

/LOADS Q REGISTER
/FROM AC
/OBTAIN ADDRESS FOR RETURN
/TO USER PROGRAM

RTJ

/RESTORE AC

/INHIBIT EERO CLOBBERING
/IN USERS memory SEGMENT
/ReSjOrE InTeRrUrT BuFfEr
/BECOMES JMP TO USER PROG,

DJR
lOB

RMfA
hit
3777

RTJ,
OVN,
/

0250

0325

0251
0252
0253
0254
0255
0256
0257
0260

1020
0000
0450
6323
0435
6262
0452
6255

0261

6323

/KBD PROCESSING
ROR
ookbd
I

LOA
UPC,

LP,

/PUT TRAPPED INSTRUCTION
/I BIT into computer
/LINC BIT
/get leftover char,
/IF ANY

AHE
JMP
KST
JMP
LHE
JMP

/LEFTOVER CHARACTER?
/YES, DELIVER IT TO USER
/NO. FRESH Character?
/YES,
GO READ IT
/NO. PAUSE?
/YES, HANG IN THERE
/till key STRUCK.
/NO, RETURN TO USER W. AC
/CLEARED

LOO
I

GRC
LP

JMP

LOO

/READ AND TRANS LATE
0262
0263
0264
0265
0266
0267
0270
0271
0272
0273
0274
0275
0276
0277
0300
0301
0302
0303
0304
0305

0011
0500
6034
1120
7602
0301
1560
3700
1120
0401
4276
1300
0000
1420
7600
6337
1120
7722
0451
63l7

GRC,

KEYBOARD CHARACTER

clr
lOB

KRSA
ADA
-175
ROR
BCL
3700
ADA
TAB
STC
LDH

/READ A CHARACTER
/CALCULATE CHARACTER CON/VERSION TABLE INDEX IN
/HALF WORDS

1
I

/ADD BASE ADDRESS OF TABLE

/HALF-WORD PICKUP ADDRESS
/get THE LINC CHARACTER.

SHD
7600
JMP
ADA
-55
APO
JMP

/IS IT AN UNDEFINABLE?

RETX

/YES, ECHO UPARROW
/IS IT UPPER CASE?

LOW

/NO,

0306
0307

1120
0011

/ITS AN UPPER CASE CHARACTER
ADA
/MAKE IT LINC CODE
I

0274
0275
0276
0277
0300
0301
0302
0303
0304
0305
0306
0307
0310
0311
0312
0313
0314
0315
0316
0317
0320
0321
0322
0323
0324
0325
0326
0327
0330
0331
0332
0333
0334
0335
0336
0337
0340
0341
0342
0343
0344
0345
0346
0347
0350
0351
0352
0353
0354
0355
0356
0357
0360
0361
0362
0363

0310
0311
0312

0451
0011
4252

APO
clr
STC

0313
0314
0315
0316

1020
0023
4242
6221

LOA
23
STC
JMP

0 36 4

0 36 2

0365
0366
0367
0370
0371
0372

/DELETE MINUS ZEROES
UPC

/SAVE IT FOR USE AFTER
/CASE CHARACTER IS OUTPUT
/get CASE character

AC
ret

/STORE FOR TRANSFER
/EXIT

/loner CASE characters
0317
0320
0321
0322
0323
0324
0325
0326

1120
0055
0451
0011
4242
4252
0500
6036

LOW

0327
0330

6350
1460
0215
6221
1020
02l2
6350
6221

LOOl

03 31

0332
0333
0334
0335
0336

ADA

/make IT LINC CODE

APO
CLR
STC
STC

LOO,

UPC

/STORE IT FOR TRANSFER
/clear LEFT OVER BUFFER

/READ CHAR AND
/CLEAR KEYBOARD FLAG
/ECHO

lOB

krba
JMP
SAE
215
JMP
LOA
212
JMP
JMP

/C,

RET
I

R.?

/NO. EXIT
/YES, THROW IN
/A FREE LINE FEED

PRINT
RET

0337
0340
0341
0342
0343
0344
0345
0346

1020
0336
6350
0500
6036
6350
0017
0261

0347

6255

/ILLEG AL character
/PRINT UP ARROW
RETX
LDA
336
PRINT
JMP
/ECHO OFFENDING
lOB
/CHARACTER
KRBA
PRINT
JMP
COM
/SET LINK BIT
1
ROL
/TO keyboard "PAUSE*' VALUE
JMP
LP
I

0350

0002

435 1
4352

4353
4354

6046
6041
5352
6141

0355

6000

0356
0357
0360

0011
4252
0001

0361

0363
0364
0365

0024
1620
1000
0004
6000

04 00

6025

/PRINT
/ENTER
PRINT,

character
CHAR IN AC

ASCI I
POP

PMODE
TLS
TSF
.-1
JMP
LINO
LMODE
JMP
0
/INITIALIZE THE TRAP PROCESSOR
clr
INI T
/clear left over character
UPC
STC
/BOILER plating FOR GUIDE
AXO
.

ENDX,
*400

SFA
BSE
1000
ESF
JMP

JMP

/RESTART
FNS. REG,
/GET SPEC
/set TRAP enable BIT
,

/READ IT BACK OUT
/RETURN

RST400

/GO TO START 400

/CONTROL ROUTINE

0373
0374
0375
0376
0377
0400
0401
0402
0 40 3

0404
0405
0 40 6

0407
0410
0411
0412
0413
0414
0415
0416
0417
0420
0421
0422
0423
0424
0425
0426
0427
0430
0431
0432
0433
0434
0435
0436
0437
0440
0441
0442
0443
0444
0445
0446
0447
0450
0451
0452
0453
0454
0455
0456
0457
0460
0461
0462
0463
0464
0465
0466
0467
0470
0471

0401
0402
0403
0404
0405
0406
0407
0 4 10

0411
0412
0413
0414
0415
0416
0417
0420
0 421
0422
0423
042 4

0425
0426
0427
0430
0431
0432
0433
0434
0435
04 36

0437
0440
0441
0442
0443
0444
0445
0 44 6

0447
0450
0451
0452
0453
0454
0455
0456
0457
0460
0461
0462

2323
1376
7676
7676
7676
7676
7656
7676
1276
7676
7676
7676
7676
7676
7676
7676
2376
7614
7676
2265
6215
1676
7676
2063
1764
2100
0102
0304
0506
0710
1176
7676
6176
7676
2425
2627
3031
3233
3435
3637
4041
4243
4445
4647
5051
5253
5455
6621
7676
7676

TAB.

2323
1376
7676

/ALTMODE-CASE/ ALTMODE -CASE
/rubqut-oel/leader-null

7 67 6

/N,
/N,

7676
7676
7656
7676
1276
7676
7676
7676
7676
7676
7676
7676
2376
7614
7676
2265
6215
1676
7676
2063
1764
2100
0102
0304
0506
0710
1176
7676
617 6
7676
2425
2627
3031
3233
3435
3637
4041
4243
44 45

TABE.

4647
5051
5253
5455
6621
7676
7676

/not used
U.
U.

/BELL/N, U,
/TAB/L, F. -META
/N,

/CR-EOL/N.
/N.
/N,
/N,
/N.
/N,
/N,
/N.
/

U.
U.
U.
U
U.

ALTMOOE-CASE/N

/N.U, /SPACE-SPACE
/EXC.PT/D8L .quotes

/number SIGN/DOLLAR SIGN/PERCENT-P, C/ AM PE RS AMD- ampersand
/APOSTROPHE-AP, /OP PAREN
/CL PAREM/»
/PLUS-+/COMMA/MINUS--/PERIOD-.
/SLASH-SLASH/ZERO-0
/ 1/2
/3/4
/5/6
/7/8
/9/N ,U,

/SEMICOLON/<
/equal sign-=/>
/?/AT SIGN
/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

/left BRACK/BACK SLASH
/RT, BRACK/UP ARROW
/BACK ARROW/N.U,
,

/ initial

0463
0464
0465

6474

ST20,

635fc

6472

start 20
setup

JMP
JMP
JMP

INIT

GOMAN

0466
0 46 7

0470
0471

6474
6356
0643
0000

/INITIAL START 400
ST400,
setup
JMP
JMP
INIT
LDF
hlt

/INITIALIZE TRAP PROCESSOR

0472
0473
0474
0475
0476
0477
0500

0472
0473

0600
6033

0474
0475
0476
0477

05 01

05 00

0502
0503
0504
0505
0506
0507
0510
0511
0512
0513
0514
0515
0516
0517
0520
0521
0522
0523
0524
0525
0526
0527
0530

0501
0502
0503
0504
0505
0506
0507
0510
0511
0512
0513
0514
0515
0516
0517
0520
0521
0522

0057
0000
1020
6356
1040
0020
4025
0640
0061
7334
0062
2017
0063
0017
1023
1062
0221
6512
0062
2677
0061
7757
1020
6033
1062
0221
6524
6017

05 2 3

0524
0525
0526
0527

GOHAN*

LIT
JMP

/THIS LANDS IN FIELD
GUIDE
/TRAP PROCESSOR RELOCATOR
SET
17
SETUP,

LDA
JMP
STA

/SET UP RESTARTS
INIT

/SET UP 20 RESTART

STC
ldf
set

RST400
0
I

/SET UP 400 RESTART
/SET DATA FIELD TO 0
/SET UP MOVE COUNT

-TABE*17
SET
2017
SET

LDA
STA
XSK
JMP
SET
2677
SET
-20
LDA
JMP
STA
XSK
JMP
JMP

.-3

/SET TO-ADORESS
/BIT 1 (2-010) SAYS USE
/SET FROM-ADORESS
/bit 1 (0-000) says USE
/INCREM. 3, GET (3)

/INCREM,2,ST0RE (2)
/INCREM. 1, SKIP IF 1«17'
LOOP AGAIN
/I NOT 1777
/SET UP FOR LEFT
/SWITCHES RESTART
/20 JMP GUIDE-S
.

GUIDE
I

,-2
17

/INC 2, STORE INTO (2)
/END CHECK

0000

ERRORS

COFX
OOKBO
ENDX
ERR
FETCH
GOMAN
CRC
GUIDE
INIT
KBO
KCCA
KRBA
KRSA
LC

LOO
LOOl
LOW

4242
4171
4250
4365
4130
4160
4472
4262
4033
4356
0515
6032
6036
6034
4225
4323
4 32 7

4317
4255
4135
M70
4136
ONE
0500
OPR
4212
0P14
OTHERS 4211
4222
OVL
4247
OVN
4134
PC
PRINT 4350
4232
0
LP

RET
RETX
RMFA
RST400
RTJ
setup
ST20
ST400
TAB
TABE
TLSA
TSFA
UPC

4221
4337
6244
4025
4246
4474
4463
4466
4401
4462
6046
6041
4252