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DIGITAL-8-12-U

December 1966

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Document:	digital-8-12-u-d
Order Number:	DIGITAL-8-12-U
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Pages:	8
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/digital-8-12-u/digital-8-12-u-d.pdf

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IDENTIFICATION
I .I

Digital—84 2-U

I .2

Incremental Plotter Subroutine

I .3

Revised June I, I966

PDP-B
LIBRARY

Digital-8-l 2-U
Page 1
2

ABSTRACT

This subroutine moves the pen of an incremental plotter to a new position along the best
straight line. The pen may be raised or lowered during the motion.
.

REQUIREMENTS

3 1

Storage

The subroutine requires one memory page (128 registers).
3.2

Equipment
Basic PDP-8

Type 350 Plotter Control and Plotter
4.

USAGE

4.l

Loading
The library tape that is supplied isa symbolic tape which has no origin setting and which ends

This tape may be assembled with a user program (which supplies an origin)
if
a
assembled
itself
dollar
or
sign ($) is supplied.
by

with the statement "PAUSE'I

4.2

Calling Sequence
The Plot subroutine is called with an effective JMS PLOTX.

The contents of the accumulat—

specify the operation of the subroutine:
C(AC)

—l:

The location registers internal to the subroutine are reset
to O and the pen is raised.

Control returns to the in-

struction following the calling JMS instruction;

C(AC)

The pen is lowered (if it was up) and is moved to the
new

C(AC)

location (see below);

The pen is raised (if it was down) and is moved to the
new

location;

The two locations following the calling JMS instructions contain, respectively, the new X
coordinate and the new Y coordinate in steps (<4096). The pen is moved from the previous location to
this new location along the best straight line with the pen up or down depending upon the contents of the

accumulator when the subroutine is called.

Control returns to the instruction following the Y coordinate.

Examples:
Initialize

Ploj with P?!) Down

Plot with Pen Up

CLA CMA

CLA

JMS I PLOT

JMS IPLOT

Return

X Coordinate

Y Coordinate

Return

PLOT, PL OTX

CLA IAC

Digital-8—l2— U
Page 2
5.

RESTRICTIONS (Not Applicable)

DESCRIPTION

6.l

Discussion
The Plot subroutine has two registers which contain the location of the last position plotted.

When the subroutine is entered, the accumulator is tested to determine if initialization is being called.
If so, the location registers are set to

O, the pen is raised, and the subroutine exits.

If it is not initiali-

zation, the subroutine compares the current pen position (up or down) with the requested one and raises or
lowers the pen if appropriate. The new X and Y coordinates are picked up and placed in the location

registers. The X and Y differences between the current location and the desired location are computed
The subroutine selects motion commands depending upon the quadrant of the new location
compared to the old. The possible motions are now parallel to either the X-axis (drum motion) or the Yaxis (pen motion) or a combined motion. The subroutine determines which of these motions to use, and

and compared.

when the new location is reached, it exits.
7.

METHODS (Not Applicable)

FORMAT

8.]

Input Data
The X and Y coordinates are specified in numbers of steps.
Increasing Y corresponds to moving the pen left.

Increasing X corresponds to

lowering the drum.
9.

EXECUTION TIME

9.l

Minimum (Not Applicable)

9.2

Maximum

9.3

Average

(Not Applicable)

This subroutine is device speed limited, although the minor subroutine, PLOTWT, could be
replaced by a routine making use of the program interrupt.
l0.

PROGRAM

l0.l

Core Map (None)

l0.2

Dimension List (None)

10.3

Macro, Parameter, and Variable Lists (None)

Digital-8-12-U
Page 3
10.4

Program Listing
/DIGITAL 8'12QU
IPLOT SUBROUTINE
/CALLING SEQUENCE
/
/
/

/
/

0200
0201
0202
0203
0204
0295
0206
0207
0210
0211
0212
0213
0214
0215
0216
0217
0220
0221
0222
0223
0224
0225
0226

INITIALIZE
PLOT WITH PEN DOHN
C(AC)= 13 PLOT WITH PEN UP
JMS PLOTX
X CO-ORDINATE (IN STEPS)
(RETURN
Y CO-ORDINATE (IN STEPS)
C(AC)=-1:
C(AC)= 03

0000

PLOTX:

7510
5220
1361
7112
7710
5227
7620
5214
3361
6504
5216
2361
6524
4370
5227
7200
6504
3361
3362
3363

SPA
JMP
TAD
CLL
SPA

/MOVE

CLA
JMP PLOT1
SNL CLA
JMP .+4
DCA PLOTPN
PLPU
JMP .+3
182 PLOTPN

/ADD
IANY
INO:

CHANGE?
CONTINUE

/LONER
/RAISE

THE
THE

PEN
PEN

ILOHER

THE

PEN

PLPD
IHAIT

FOR
/CONTINUE

JMS PLOTNT
JMP PLOT1
CLA
PLOTA.
PLPU
DCA PLOTPN
DCA PLOTNX
DCA PLOTNY

JMS PLOTNT
I

/DIGITAL
/PAGE 2
/PICK UP

0243
0244
0245

PEN?

RTR

JMP

0242

THE

CONTINUE
PEN STATUS

/N0:

PLOTA
PLOTPN

4370

1362
7141
1600
7420
7041

AC=”1)

5600

0227
0230
0231
0232
0233
0234
0235
0236
0237
0240
0241

/RAISE

THE

FLAG

PEN

COPORDINATE
CO-ORDINATE

PLOTX

8~12*U
ARGUMENTS

TAD
PLDT1.
CIA CLL
TAD I PLOTX
SNL

/FETCH

PLOTNX

IFORM
/L=0:

CO—ORDINATE

NX~NPX
NX<NPX

cIA

3364

DCA

7004
3367

RAL

PLOTDX

/ABSOLUTE

2200

DCA
TAD
DCA
182

PLOTHV
I PLOTX
PLOTNX
PLOTX

1363
7141
1600

TAD
CIA
TAD

PLOTNY
CLL

/SAVE SIGN BIT
/SET NEH
IPREVIOUS X
/INCREMENT POINTER
/FETCH PREVIOUS Y CO-ORDINATE

7420

SNL

1600
3362

PLOTX

/FORM
/<=0:

VALUE

NY-NPY
NPY<NY

DIFFERENCE

Digital-8-12-U
Page 4
6246
0247
0250
0251

7041

CIA

3365

DCA

PLOTDY

1367
7004

TAD

PLOTMV

RAL
DCA

PLOTMV

0252

3367

0253

1600

0254
0255
0256
0257
0260
0261

3363

0262
0263
0264
0265
0266
0267
0270
0271
0272
0273
0274

2200

1364
7141
1365

TAD
DCA
182
TAD

I PLOT X
PLOTNY
PLOTX

CIA

CLL
PLOTDY

TAD

‘

PLOTDX

7620
5275
1364

SNL

CLA

/L=0:

JMP
TAD

PLOT?
PLOTDX

/REVERSE

3366

DCA
TAD
DCA
TAD
DCA
IAC
AND
TAD

PLOTNA

1365
3364
1366
3365

7001
0367

1342
5300

JMP

1367

7110

1345
3366
1766
3340
1367
1350
3367

1767
3331
1364

7110
3366

1364
7040
3367
2367

7410
5600
1366
1365
3366
1366
7140
1364
7630
5340

0000
1364
7041

DELTA

NUMBERS

PLOTNA
PLOTDY

/SET MAJOR MOTION
/INSTRUCTION

PLOTMV
PLOTTl
.+4

8’12-U

PLOT2 9
TAD
CLL RAR
TAD PLOTTZ
DCA PLOTNA
TAD I PLOTNA
DCA PLOT4
TAD PLOTMV
TAD PLDTT3
DCA PLOTMV
TAD I PLOTMV
DCA PLOTDB
TAD PLOTDX
CLL

DELTA

PLOTDY
PLOTDX

/DIGITAL
/PAGE 3

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

VALUE OF DIFFERENCE
ISAVE SIGN BIT
/BIT 10(1): DRUM‘DONN(POSITIVE)
/BIT 11(1)=PEN-LEFT (POSITIVE)
/SET NEH
IPREVIOUS Y
/INCREMENT POINTER

/ABSOLUTE

PLOTMV

-/SET

COMBINED

MOTION

RAR

'DCA PLDTNA
TAD PLOTDX
CMA
DCA

PLOTMV
ISZ
PLOTS O
SKP
JMP I PLOT X
TAD PLOTNA
TAD PLOTDY
DCA PLDTNA

TAD

PLOTNA

CMA

CLL
PLOTDX

TAD
SZL
JMP

PLOTMV
/ALL

DONE

CLA
/SINGLE

PLOT4

PLOTDB.
TAD PLOTDX
CIA

MOTION

/COMBINED

MOTION

Digi’ra 1-8—1 2-U
Page 5
@334
@335
@336
@337

1366

TAD

PLOTNA

3366
437@
5316

DCA

PLOTNA
PLOTNT
PLOTS

@34@
@341

@@@@

@342
@343
@344
@345
@346
@347
@35@
@351
@352
@353
@354
@355
@356
@357
@36@

@343

5336

6511
6521
@346
6512
6514
@351
6513
6523
6515
4355
@@@@

JMS
JMP

PLOT4:
JMP 0-3

PLOTTl.
PLPR
PLPL

.+1

PLOTTZ.
PLDU
PLDD
PLOTT3.
PLDU PLPR
PLUD PLPL
PLDD PLPR
JMS .+1

.*1

PLDD

5755

JMP

@37@
@371
@372
@373
@374

@@@@
@@@@

.*1
/UP-RIGHT
/UP-LEFT
/DONN-RIGHT
/DONN-LEFT

PLPL
I

/DIGITAL
/PAGE 4
@@@@

/DRUM-UP
/DRUM-DONN

6514
6521

@361
@362
@363
@364
@365
@366
@367

/PEN-RIGHT
/PEN'LEFT

PLOTPN.
PLOTNX:
PLOTNY,

.—3

8-12-U

@@@@

PLOTDX,
PLOTDY.
PLOTNA:
PLOTMV,

@@@@

SSGQ

PLOTNT.

fl@@@
@@@@
@@@@

65@1
5371
65@2
577@

PLSF
JMP .-1
PLCF
JMP I PLOTNT

PAUSE

/HAIT
/NOT

FOR
YET

/CLEAR
/EXIT

DONE

FLAG

Digital-B-IZ-U
Page 6
PLOTA

PLOTDB
PLOTDX
PLOTDY

022%

@331

PLOTMV

@364
@365
@367

PLOTNA

0366

PLOTNX
PLOTNY
PLOTPN
PLOTTI
PLOTT2
PLOTTS
PLOTNT
PLOTX
PLOTl
PLOTZ
PLOTS
PLOT4

@362
0363
0361
B342
@345

035%
037%
0200
@227
0275
0316
@346