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DIGITAL-8-12-S

December 1966

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Document:	digital-8-12-s-d
Order Number:	DIGITAL-8-12-S
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Pages:	8
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IDENTIFICATION
Product Code:

Digital 8-12-S

Product Name:

ODT - II Revised

Date Created:

December 7 ,

Maintainer:

Software Service Group

966

PDP-B
LIBRARY

Digital-8-1 2-S

Page 2
2

ABSTRACT

ODT-I (octal debugging tape) is an aid used in debugging a PDP-8 program by faci litating
communication with the program being run
The communication between operator and program is via the
I

ASR-33 Teletypewriter

ODT-I features include register examination and modification, binary punchouts, control
word search ing, octal dumping and instruction trapouts to ODT-I contro break-traps)
ODT-I
makes no use of the program interrupt facility and is restricted to one memory module.
I

transfer,

(

REQUIREMENTS

3.1

Storage

ODT-li requires 600 (octal) registers and resides in memory between 7000 and 7577 (or 1000 577)

3.3

ODT-1

addition,

uses register 0005

Equipment
Standard PDP-8

USAGE

4.1

ODT-ll is loaded by means of the Binary Loader (see Digital-8-2-U)
4.1.1

Place proper ODT-ll tape in reader (either high or low version).

4.1.2

Set the

4.1 .3

SWITCH REGISTER to 7777 and press LOAD ADDRESS.

using the 750 Reader, put switch 0 down and press START.

If using

put switch 0 up and press START.

the 33-ASR Reader,'

4.1.4

Read the binary tape of the program to be debugged into core as above.
program to be debugged does not overlap ODT-I and vice versa)

(Make sure that the

4.4

Start-Up

The starting address of ODT-ll
4-4.

Set

4.4,2

7000 (1000 is low version).

ODT-ll starting address in the SWITCH REGISTER (1000 or 7000)

Press

LOAD ADDRESS, and press START

ODT-ll is now running and is awaiting commands

from the 33-ASR Keyboard
5.

RESTRICTIONS

5.1

Status Active Registers

Register 0005 (page 0) is used by ODT-I when executing a
break -trap
This register is fi led
with an address within ODT-I
When the operator requests a break-trap, ODT-ll saves the
instruction at the location of the trap and replaces it with the
instruction, JMP
5, thus returning control
I

by ODT-I

Digital-8-1 2-S

Page 3

ODT-II

version).

ODT-II also uses 600 (octal) locations from 1000 - 1577 (low version) or 7000 7577 (high
The programmer must be certain that his program to be debugged does
not overlap ODT-II

5.2

Status Core

ODT-II will not operate outside of the core memory modu le in which it resides

DESCRIPTION

octal debugging program for the PDP-8

A number is a string of digits taken as octal

Teletype (33-ASR).
I

characters or are

Operator communication occurs on the
Other characters are either control

legal

ODT-II 's most useful features is the "break-trap". When debugging a program,
it is
o ten desirable to allow control to flow up to a
certain point, at which time the programmer would like to
examine the contents of the accumulator, the link, and various other
registers of his program
To facilitate this
ODT-II will insert in the user's program a jump instruction into
ODT-II, which will cause the
C(AC) and C(L) to be preserved. ODT-II will then print out the break
location and the contents of the
possible to move the break-trap and continue the program,
restoring
the C(AC), C(L), and the trapped instruction.
The trapped instruction is executed and control is returned
to the user s program.
•

6.1

Discussion

6.1 .1

Commands

6.1 .1 .1

Slash (/)

The register examination character
/ causes the contents of the register addressed by the preceding expression to be typed out in octal. The register
is then opened for modification and the
location
sequence reset to the address.

Example:
1/

0027

(In all

examples, everything underlined is typed by ODT-II;
everything

typed by the user.)
6.1 .1 .2

return w,

closed.

Carriage Return

not underlined

(^ )

The value of any expression that has been typed by the user
immediately preceding the carriage
'
rep oce the contents of the open register, if any
register was open, and
registef wiU be
If nothing has been typed by the user,
the contents will not be changed.

Example:
1/

Q027

0027 14

unchanged

DigIfal-8-1 2-S

Page 4
6.

Line-Feed

)

(

|
The line-feed has the same effect as the carriage-return, but,
register is opened and its contents typed

addition, the next sequential

Example:

0027 i

1/
6.1

0002/ 0077

0002/ 0077
.4

unchanged.

0014.

0027 14|

Any

legal Character

Any character that is neither an octal digit nor a valid control character
line to be ignored

causes the current

Example:
19
6. 1

Single Quote (')
location specified before the (').

the break-trap,
6.

if any,

will be inserted.

All indicators and registers will be restored

and

Typing (') alone is an error.

Double Quote (")

Conditions ODT-II to insert a break-trap at the location
specified before the ("). If no such
ocation was specified, ODT-II removes the previous
breakpoint. A breakpoint is actually inserted only
when a goto ( ) or proceed ('.) is executed. ODT-II will remove
the instruction at the break location and
will save It for future restoration. The instruction
at the break location is only executed after the
"
proceed
s n vpn
I

Exclamation ( I)

Proceed from a break-trap. The C(AC) and C(L) are
restored, the trapped instruction is ex
ecu ted , and control transfers to the user's program

NOTE; If a trap set by ODT is not encountered by the ob|ect
(user's) program
the breakpoi nt nstruction will not be removed
i

7000), however, will restore the original
The breakpoint will be reinserted when goto
(') or proceed (.') is executed.
When a breaktrap IS encountered in the user's program,
ODT-II will type out the location of the trap, a right
parenthesis, and the contents of the accumulator.
The accumulator and link are saved in registers
7350 and
351, respectively, (1350 and 1351 for low version). These
registers may be examined (and modified)
^
m the normal manner by use of the slash (/) control character.
•

r
rinstruction.

DigItal-8-12-S

Page 5
6 1.1 .8
.

6.1

M
Typing the letter

opened for modification

M causes the contents of the mask register (see 6

Initial ly,

this value

set to

)

to be printed

and

7777,

6.1
.1

< (Left Angle Bracket)

Typing this character causes the contents of the lower search limit register (see 6.1.1.11) to
be printed and opened for examination, initially, this value is set to 0001
.

.10

> (Right Angle Bracket)

Typing this character causes the contents of the upper search limit register (see 6
be printed and opened for examination. Initially, this value is set to 6777.
6.1

1 )

NOTE: The registers named M, <, and > are within ODT-II and have addresses
7550, 7551, and 7552, respectively.

.11

Word Searches

Word searching using ODT-II is similar to word searching using DDT (see Digital-8-4-S)
The
searching operations are used to determine If a given quantity is present In any of the
registers of a particular section of memory. The search is Initiated by the command:
.

KW
Where K is an octal expression. ODT-II will perform a word search and print the address
and contents of every register in the desired section of memory whose contents, when
masked by C(M) are
equal to the value of the expression K. The search continues between the limits
specified by C(<) and
6.1

Example:

Search locations 2000 to 4000 for

7777

<
>

0001

6777

7000
2000
4000

2000
AlUZ,

Set the mask
Set the lower limit

Set the upper limit
Initiate the search

AAr(j7

etc
.1

.12

Punch Commands
LU

Digifal-8-12-S

Page 6

Where K is the Initial address (octal) and
Is the final address (octal) of the register to be
The computer will halt, al lowing the operator to turn the Teletype off ne and to punch leader
1

punched
codes.

Putting the Teletype back on line and depressing CONTI NUE initiates the actual punching of the

block
The punching terminates without punching a checksum to a low subsequent blocks to be punched
and an all inclusive checksum to be punched at the end
This procedure is optional however, and the
.

user may punch individual ly checksummed blocks
See 6.1.1,13 for a descri ption of the checksum
mand
If subsequent blocks are desired, turn off the punch before typing the pertinent commands
.

com-

6.1 .1 .13

(Checksum Command)

Typing an asterisk (which does not print) causes the program to punch out the accumu lated
checksum
The program wi
then halt to al low the operator to turn the Teletype off ine, produce trailer
code (200), and remove the tape
The operator shou Id then turn the punch off, turn the Teletype on line
and depress CONTI NUE to resume ODT-I operation
.

6 1.2
.

Command Summary
Slash (/)

Carriage Return

Line-Feed

Closes register and opens the next one

legal Character

closed

Current line is ignored

ODT-I

types ?

Goto

Double Quote (")
Exclamation (1)

Set a break-trap.
Proceed from trap.

Examine (and modify) mask
Examine (and modify) lower search limit
Examine (and modify) upper search limit
Word search command
Separate punch arguments
Punch in binary
Punch checksum

<
>

W
Semicolon (;)
Alt Mode
Asterisk (*)

6.2

Examples and/or Applications

6 2.1

Symbols for representing "invisible" Teletype actions:

Single Quote (')

(CR)
(LF)

(ALT)
(*)

(H)
(C)

(PON)
(POF)

(TON)
(TOF)
(LEAD)
(TEXT)

(CKSM)

=
=
=
=
=
=

Carriage Return
Line Feed

Alt Mode

Nonprinting Asterisk
Halt

Continue

Punch On
Punch Off
= Teletype On
= Teletype Off
= Production of Leader
=
=

= Punching of Text
= Punching of Checksum

Digital-8" 2-S
1

Page 7

6.2.2

Underlined functions and expressions are those produced by ODT-li.

6.2.3

Brackets enclose comments local to this description

6.2.4

Examples of Register Examination and Modification

100/ 1234 7777 (CR)
100/ 7777 (CR) (LF)

{CFT
010i/T564

[Examine and modify.]
Examine only
Examine next
Examine next.

[

(LF)

(LF) (CR)

[

0102/ 4567 2222X? (CR) (LF)
102/ 45 67 22222? (CR)(LF)
102/ 4567 2222 (CR) (LF)
102/

6.2.5

[

]

legal character,
]

More than four integers typed

Correct modification

Success at last

2^ (CR) (LF)

]

Word Searching Example

M 7777 (CR) (LF)

[Examination of parameters.]

< 0001 (CR) (iFy
> 6777 (CR) (Uy
7200W (CR) (LTT

[Search

0150/7200 (CR) (LF)
1216/7200 (CR) (LF)
M 7777 600 (CR) (LF)

[Set mask for indirect and page bits.]

< 0001 200 (CR) (LF/
400W (CR) (LF)

[Search

1426/3403 (CR) (LF)

other pages

1627’/5400

references to page 0 from

]

[

HLT looks like an indirect ref. to page 0.

]

[Searching completed .]

M 0600 7777 (CR) (LF)

[

for all Indirect

(CR) (LF)

itf)

6777 (CR) {Wy

Octal

CLA instructions .]

for all

[Set limits to exclude page 0.]

1705/7402 (CR) (LF)

6.2.6

[

Reset mask]
and lower limit.

]

Dump Example

V/e wish to dump core between 1000 - ’005]

M 7777 0 (CR) (LF)

[

0001

1000

(ClT(LF)

6777

1005

(CR) (Ir

Set

]

imi ts to encompass dump area

]

1001/0002 (CR) (LF)
1002/0003 (CR) (LF)
1003/0004 (CR) (LF)
T004/0005 (CR) (LF)
1006/0006 (CR) (LF)
M 0000 7777 (CR) (LF)
(CR) (TFT
(CR) (TfT

Since
is typed alone, the word searched for Is 0
The result after masking each register with 0 is, of
[

100S70OT“ (CR) (LF)

1000 0001
1005 6777

Set mask to 0

W (W(LF)

<
>

[

course, 0 so all comparisons appear to the program

equal and hence all unmasked contents are typed,
constituting a dump

[

Reset parameters.

]

Digital-8~12-5

Page 8

6.2.7

Example of Paper Tape Punchout (Binary Format-)
[

[

The punchout of page 1 and the first 5 O 3 registers of page 3.]
The TTY is assumed to be on line and the punch turned off.

]

200;377(ALT) {_H) (TOF) (PON) (LEAD) (TON) (C) (TEXT) (POF) (CR) (LF)
600;647(ALT) (_H) (PON) (C) (TEXT) (*) (CKSM) (H ) (TOF) (LEAD) (POTT(TON) (C) (CR) (LF)
[

[

6.2.8

ODT-1 now running in input mode waiting further commands
Remove tape from punch
1

]

Examples of Using Break-Trap Mode
241"

(CR) (LF)

[Set break to occur at user's loc. 241 .]

241/7200 (CR) (LF)

[

200'

[Enter user's program at location 200.]

(CR) (LF)

0241 )0324 (CR) (LF)
7351/0001 (CR) (LF)
241/7200 (CR) (_LFr

[

Examination shows that trap inst

not yet inserted

Break-trap occurs, and C(AC) typed.]
Examination of state of link at break
.

]

[Any amount of DDT functions may be indulged]
[in at this point before continuing.]

253"
‘

(CR) (LF)

0253)0000 (CR) (jJF)
"

(CR) (LF)

(CRj (LF)

[Break-trap reset at loc. 253.]
[User's program continued from point of last break (241 ).

[Second break occurs.]
[

Break-trap mode deactivated.]

[User's program continued without any traps set.]

[To reenter ODT-II, user would have to start at 7000.
7.

METHODS (Not Applicable)

FORMAT (Not Applicable)

EXECUTION TIME (Not Applicable)

PROGRAM

]