Digital PDFs

DIGITAL-8-20-U

December 1965

6 pages

Original

0.3MB

Document:	digital-8-20-u-d
Order Number:	DIGITAL-8-20-U
Revision:
Pages:	6
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/digital-8-20-u/digital-8-20-u-d.pdf

OCR Text

IDENTIFICATION
I .I

Digital-B-ZO-U-Sym

I .2

Character String Typeout

I .3

October 22, I965

PUP-8
LIBRAFIY

Digital-8-20-U-Sym
Page I
2

ABSTRACT

A basic subroutine to type messages stored internally as a string of coded characters.

All

ASR-33 characters are legal.
3.

REQUIREMENTS

3 I

Storage

This subroutine uses 59 (decimal) core memory locations.

3.3

EQUIPMENT
Basic PDP—8

USAGE

4.]

This subroutine may be placed in core through the use of the Binary Loader, which is com—
pletely described in Digital-8—2-Rim. The library tape supplied is symbolic.

4.2

Calling Sequence
Call with a JMS with the starting address of the character string in the AC.
following the calling JMS.

Return will be

to the instruction

RESTRICTIONS (Not Applicable)

DESCRIPTION

6 I

Discussion

The ASCII character set breaks naturally into two major groupings:

characters represented

and characters represented by codes 30I

through 337. Characters with these
by codes 240 through 277;
codes may readily be handled by representing them internally as stripped 6-bit codes. See Digital -8-I8—U-Sym and Digital-8-l9—U-Sym for a complete discussion of how this is done.
The following are special characters:

Character

Code

EOT

204

WRU

205

206

BELL

207

Line Feed

2l2

Return

2I5

300

ACK

374

ALT MODE.

375

RUBOUT

377

These special characters are represented by codes which conflict with the groupings from 240 to 277 and
30I to 337. Consequently when these characters must be output, they are treated as exceptions and

Digital-8-20—U-Sym
Page 2

developed by special methods as described in Digital-8-18-U-Sym and Digital-8-l9-U-Sym.
these programs permits the development
ofgl_l_ the codes listed above. This program does.
7.

METHODS

7.]

Discussion

Neither of

Internally characters are represented as 6-bit stripped characters and are packed two to a
The stripped character 00 is used to indicate that the following character is a special character.
For example, @ may be developed by packing 0000.

word.

Since the appearance of 00 indicates that the next 6-bit group is to receive special treatment, 64 special characters are possible. This is many more than necessary to accommodate the ten
special characters listed above that are required for ASCII typeout. The 6-bit group 00000l is therefore
used to indicate the end of a given character string since it is not needed for regular ASCII output.
The method is straightforward.

The first message word is picked up and the two trimmed codes

masked out. Two iumps to the subroutine tagged TSCC2 are made in order to type the two characters.
TSCC2 tests first to determine if the special character flag is set indicating that the current character is
special. If so, a JMP to TYPSP is executed. If not, a test is made to see if the current code is 00. If
so, the special character flag is set but no typeout ensues. If not, a regular character is being processed
and is typed.
The TYPSP section of coding processes special characters.

The special characters may be

classified as:

Special Character
300

Comments

Logically the lowest element of extended group 301
through 337.

374,375,377

Least significant two digits similar to those in group

240 to 277.

204,205,206
207,212,2I5

Least significant two digits similar to those in group
30l

through 337.

In order to develop the correct output, TYPSP changes the SPA command in SWITCH to a

SMA command for all special characters but 300.
8

8.4

FORMAT
Miscellaneous
Refer to Digital-8-18-U-Sym and Digital-8-I9-U—Sym for further format and code description.

EXECUTION TIME (Not applicable)

Digital-B-ZO-U-Sym
Page 3
10.

PROGRAM

HL4

Program Listing
/DIGITAL 8-23- U
/CHARACTER STRING
/CALL WITH STRING
/C(AC); ALL CODES
IRETURN FOLLOWING

@209

3369

8231

3262

@262
8293
$294
92%5
9206
£297
@219
9211
@212
@215

3264
1662
7912
7012
7012
4214
1662
4214
2262
5295

2214
6215
@216
3217

3900
$265
5265
1264
7649
5251
1263
745%
5227
4259
5614
2264
5614

0221
8222
@225
@224
@225
3226
B227
6259
@231
9252
$235
@234
0235
@236
@257
@249
@241

5264

TYPSTG,

TSCCl,

TYPE-OUT
ADDRESS IN
MAY BE DEVELOPED
THE JMS

DCA TEMQ
DCA FLAG
TAD I TEMQ
RTR

/STORE INITIAL ADDRESS
/CLEAR FLAG
/PICK UP DATA
/ROTATE 6 BITS RIGHT

RTR
RTR
JMS
TAD
JMS
ISZ
JMP

Tsccz,

TYPAT,

TSCCZ
I TEMQ
TSCC2
TEMQ
TSCCl

/TYPE FIRST CHARACTER
/PICK UP DATA
/TYPE SECOND CHARACTER
/INCREMENT STORAGE ADDRESS
/GO BACK FOR MORE

K77

/MASK OFF 6 BITS
ISAVE CHARACTER
ITEST ”SPECIAL” FLAG

AND
DCA
TAD
szA
JMP
TAD
SNA
JMP
JMS
JMP

TEMR

FLAG
CLA
TYPSP
TEMR
.+3
PRINT
I TSCCZ

ISZ FLAG
I TSCC2

JMP

TYPSP,

1263
7941
7459

DCA
TAD
CIA
SNA
JMP
IAC
SNA
JMP
TAD
DCA
TAD
JMS
TAD

FLAG
TEMR

@242
9245
3244
@245
9246
@247

5225
7391
7659
5636
1271
5252
126$
425$
1272
3252
5614

0259

9663

PRINT,

9251
9252

1266
7510

szTCH,

TAD M43
SPA

TYPAT
CLA
I TYPSTG

SKIPMA

SWITCH
TEMR
PRINT
SKIPPA
SWITCH
JMP I TSCC2

/SET: TYPE SPECIAL
/NO: REGULAR CHARACTER
/IS IT_ZERO?
/YES: SET FLAG
/NO: PRINT IT
/RETURN
/SET ”SPECIAL" FLAG
/EXIT
/CLEAR ”SPECIAL”
/TEST FOR "D”

FLAG

ID: TYPE ”O”
/TEST FOR 01

/YES: EXIT CODE
IALTER INSTRUCTION
/TO BE "SMA"
/TYPE CHARACTER

/ALTER INSTRUCTION
/TO BE "SPA”
IRETURN

/COMPARE WITH 40
/OR SMA FOR SPECIAL

CODES

Digital-8-20-U-Sym
Page 4
o253
d254
0255
6256
3257

1267
1270

TAD
TAD

6046
6941
5256

026u
D261

5650

TLS
TSF
JMP 0'1
CLA
JMP I PRINT

7260

C193
C246

/CONSTANTS AND
D262
3263
@264
3265
2266
0267
9270
0271
3272

9900
0099
@989
@677

TEMQ,
TEMR,
FLAG,
x77,

Clam,
024a,
SKIPMA,

190
249
SMA

SKIPPA,

SPA

7740
3139
0249

C106
C248

FLAG
K77
M46

FRINT
SKIPMA
SKIPPA
SWITCH
TEMQ
TEMR
TSCCl
TSCC2

TYPAT
TYPSP
TYPSTG

7500
7510

G
9

TEMPORARY REGISTERS
/CONTAINS STRING ADDRESS
/CONTAINS 6 BIT CHARACTER
/"SPECIAL' FLAG

77
-49

5267
0270
@264

6265
0266
$259
@271
6272
0252
9262
@263
0205
0214
9225
0231
6206

11.

DIAGRAMS (Not Applicable)

12.

REFERENCES

12A

Other Library Programs

Digital-8-18-U-Sym and Digital-8-19-U-Sym