Commodore PET User manual

1

PET-CBM
Personal
Co.puter
Guide
Carroll s. Donahue
Janice K. Enger
OSBORNE/McGraw-Hill
Berkeley, California

Published by
OSBORNE/McGraw-Hill
630 Bancroft Way
Berkeley, Califomia 94710
U. S. A.
For information on translations and book distributors outside of the U. S. A. ,
please write OSBORNE/McGraw-HiII
at the above address.
PET-CBM PERSONAL COMPUTER GUIDE
1234567890 0000 89876543210
ISBN 0-931988-30-6
Copyright © 1980 McGraw-HiII, Inc. Ali rights reserved. Printed in the United States of America. No
part of this publication may be reproduced, stored in aretrieval system, or transmitted in any form or
by any means, electronic, mechanical, photocopying, recording or otherwise without the prior written
permission of the publishers.
Cartoons by Erfert Nielson.
The definitions on the back cover are adapted, with permission, from Webster's New World Oiction-
ary, Second College Edition. Copyright © 1980 by William Collins Publishers, Inc.
The programs in this book were printed on aCommodore CBM Model 2022 Tractor Printer.

Table of Contents
Preface
1. Introducing the PET
Communicating with the PET
ROM and RAM
BASIC Programming
PET Models
Features
2. Operating the PET
Unpacking
Cassette Hookup
Key top Film Covering
Startup
Keyboard
Keyboard Entry
PET Key Groups
Screen Display
Cassette Tape Drive
Cassette Operation
Cassette Tape Controls
Cleaning and Maintenance
Cleaning and Demagnetizing the Tape Head
Care of Cassette Tapes
Elementary Troubleshooting
xi
1
1
2
3
3
5
7
7
8
9
10
11
14
15
32
33
34
36
38
39
40
42
v

3. Programming the PET
47
Calculator or Immediate Mode
47
AOne-Line Program 49
Reexecuting in Immediate Mode
51
Modifying aProgram
52
Elements 53
Numbers 53
Strings 57
Variables 58
Operators
62
Arrays 69
Functions
71
File Names 74
Writing BASIC Programs 76
Line Numbers 76
BASIC Statement Groups 78
Developing aProgram 84
Modification Example Tasks 107
4. PET BASIC 111
Format Conventions 112
BASIC Commands 112
CLR
112
CO NT 112
LIST 113
LOAD 114
NEW 117
RUN
117
SAVE 119
VERIFY
120
BASIC Statements 123
CLOSE
123
CMD 124
DATA 125
DIM 126
END 127
FOR .NEXT [STEP] 127
GET 129
GET*
130
GOSUB
131
GOTO
131
IF.
.THEN
131
INPUT 133
INPUT*
134
LET =135
ON. . GOSUB 136
ON. .GOTO 136
OPEN
137
POKE
143
PRINT 143
PRINT*
145
READ 146
REM
147
RESTORE
148
VI

4. (Contlnued)
RETURN
STOP
WAIT
BASIC Arithmetic Functions
ABS
ATN
COS
EXP
INT
LOG
RND
SGN
SIN
SOR
TAN
BASIC String Functions
ASC
CHR$
LEFT$
LEN
MID$
RIGHT$
STR$
VAL
BASIC Format Functions
POS
SPC
TAB
BASIC System Functions
FRE
PEEK
ST
SYS
TI. TI$
USR
User-Defined Function
DEF FN
5. Making the Most of PET Features
Keyboard Rollover
Buffer
Two-Key Repetition
Strings
Concatenating Strings
Numeric Strings
Programmed Cursor Movement
The PRINT Statement
The CHR$ Function
Arithmetic
Addition
Subtraction
Multiplication
148
148
149
150
150
150
150
151
151
152
153
154
154
155
155
156
156
156
156
157
157
158
158
158
159
159
159
160
161
161
162
162
163
163
163
164
164
167
167
174
177
180
180
182
185
185
188
189
190
202
215
vii

5. (Continued)
Graphies
Graphies in Calculator Mode
Programming Graphies
Summary
Animation
Time Delay
Programming Character Placement
Summary
Files
Program Files
Data Files
File Handling
Writing aData File
Reading aData File
Alternate Character Set
Features of the Alternate Character Set
BASIC
Word Abbreviations
Setting the Clock
Digital Display Clock
POKE to the Screen
Calculating the Screen Address
Generating Random Numbers
6. System Information
Organization of the PET System
Memory Map
PET BASIC Interpreter
BASIC Statement Storage
User Program Area Initialization
Data Formats
Array Header
Assembly Language Programming
Appendices
A. PET ASCII Codes
B. PET Error Messages
Operating System Error Messages
C. Program Examples Solved
D. BASIC Bibliography
E. PET Newsletters and References
F. Conversion Tables
Hexadecimal-Decimal Integer Conversion
Powers of
Two
Mathematical Constants
Powers
of Sixteen
Powers
of T en
G. Variations for Original ROMs (Revision Level 2)
H. PET Features
Index
viii
225
225
229
231
232
232
233
237
237
239
239
240
242
255
273
277
278
281
285
288
288
291
303
303
308
310
312
315
317
322
329
347
361
366
369
387
389
393
394
400
400
401
401
403
425
427

FIGURES
1-1 Three Models of the Commodore PET
4
2-la
Front View of Compact Keyboard PET
8
2-lb
Front View of Full Size Keyboard PET
9
2-2 Back
View of PET
10
2-3 Full Size
PET Keyboard 12
2-4 Compact
PET Keyboard 13
2-5 The
PET Video Screen 32
2-6 The
8x8 Dot Matrix
33
2-7
PET Cassette Tape Drive 34
2-8 Inserting aTape Cassette 35
2-9
PET Cassette Tape Head 39
2-10 ATypical Tape Head Demagnetizer
40
2-11
Write Protect Notches
41
2-12 PET Internai View
43
2-13 Memory Deviee Unconnected
44
2-14 Extractor Tooi
45
2-15 RAM Numbering
46
4-1
Logical Files 139
5-1 Odd/Even Division of PET Keyboard 170
5-2 Odd/Even Three-key Rollover
171
5-3 Draw the Square
228
5-4 Make Program Statement from Graphies 230
5-5 Using PRINT:#:
244
5-6 MAIL. PRINT:#: 252
5-7
Read aData File 256
5-8 MAIL. INPUT:#:
264
5-9 Format Printing Using GET:#:
272
5-10
Standard/ Alternate Character Set Decision 274
5-11 Standard to Alternate Character Set
276
6-1
PET Block Diagram 304
6-2 Principal Pointers in User Program Area
311
6-3 BASIC Statement Storage 312
6-4 User Program Area on Power-up
316
lx

TABLES
2-1 Special Symbols as Program Operators 19
2-2 Graphie Character
Keys
21
3-1
Special String Symbols 58
3-2 Reserved Words 62
3-3 Boolean Truth Table 67
3-4 Operators 69
4-1 Physical Deviee Numbers 140
4-2 Secondary Address Codes
141
4-3
ST Values for Tape 1/0 162
5-1 Addition Operations
181
5-2 Keyword Abbreviations 280
6-1 PET Memory Allocation by 4K Blocks 304
6-2
PET Memory Map (Rev. 3 ROMs) 334
6-3
PET BASIC Keyword Codes 313
6-4 ASCII Standard 7-Bit Codes 327
6-5
PET Screen Memory 7-Bit Codes 328
G-l PET Memory Map (Rev. 2 ROMs)
41L1
x

Preface
The personal computer field was already brimming with excitement when
the Commodore
PET@ entered the scene in late 1977. A minimum PET system,
housed in aself-contained
unit with custom keyboard, video display, and tape
cassette, cost
just $595.
The
PET was an immediate sales success. Many thousands of units have
been sold, and
PET user groups are springing up ail over.
The
PET has surely become famous as one of the first popular personal com-
puters.
It has also become widely known -indeed infamous -as having the
most meager literature auser
has ever had to face. That is why this book has been
written.
After reading this book vou will have agood understanding of what aper-
sonal computer -especially the
PET -can be expected to do for vou. Certainly
as important as knowing what vou can do with apersonal computer is knowing
what vou can't do. Sy examining the capabilities and limitations of the PET. vou
will have agrasp of what vou can realistically expect apersonal computer to do
for
Vou - which is important ifvou have apersonal computer, or Vou are thinking
of getting one.
There are numerous programming examples throughout this book; by
reproducing these examples vou
will quickly get your PET working. These exam-
pies are thoroughly described and documented so vou can leam
how and why the
xi

programs work. It is the "how" and the "why" that are important if vou want to
learn how to make your
PET work efficiently for vou.
This book
is acomplete guide to the use of the PET computer.
Chapter 1
is ageneral introduction to the personal computer and BASIC
language.
Chapter 2describes
how to operate the PET keyboard, display seree n, and
magnetic tape cassette unit;
it also describes rudimentary troubleshooting tech-
niques.
Chapter 3introduces vou to BASIC. the programming language of the
PET.
Chapter4 is an alphabetical reference of PET BASIC commands, statements.
and functions.
Chapter 5describes "features" and programming quirks of the
PET -and
how to get around limitations of PET BASIC. You will find this chapter highly
useful in understanding your
PET and how to really go about programming it.
Chapter 6contains useful system information and describes such tech-
niques
as how to execute assembly language programs under PET BASIC.
Asummary of reference material
is contained in appendices to the book.
The chapters
are divided, roughly, into three technical levels. as follows:
1. If vou are anovice who wishes to use pre-written programs. vou can get
by
with the loading and editing techniques described in Chapter 2.
If vou find using the PET to be alot of fun at this stage, and vou
want to learn more about computers. arecommended book is An
Introduction to Microcomputers: Volume 0- The Beginner's Book,
Osborne/McGraw-HiIL 2nd Edition, 1979.
2. If vou are abeginning programmer. and vou want to write your own pro-
grams in
PET BASIC, then Chapter 3 will get vou started. In addition,
detailed descriptions of individual BASIC statements are given in
Chapter
4.
3. You will probably find that your programs occasionally do odd things.
These peculiarities are accounted for in Chapter 5 - necessary reading
for the advanced programmer. In Chapter 5vou
will find coverage of
topics
su ch as Extended Precision Arithmetic and File 1/0. The system
information in Chapter 6
is written for experienced programmers who
need to know about PETs memory layout. for example. so vou can write
assembly language subroutines to be run under PET BASIC.
Interfacing the
PET to external devices is such alarge topic in itself that a
separate book
is devoted to it. This Personal Computer Guide concerns itself only
with the PET keyboard, display screen, and magnetic tape cassette unit. the latter
either built-in or provided externally.
See the references listed in Appendix Efor
sources
of interfacing information on other peripheral input/output devices
available for the
PET.
xii

"There's a new PET in the House"
ACKNOWLEDGMENTS
The name PET is aregistered trademark with regard to any computer pro-
duct. and
is owned by Commodore Business Machines. a division of Commodore
1nternational. Permission to use the trademark na me PET has been granted by
Commodore Business Machines. and is gratefully acknowledged. Special thanks
are due Mr. Dennis Barnhart. Mr. Lawrence Perry. and Mr. Robert Leman of Com-
modore Business Machines, Santa Clara, California for the valuable assistance
and
support they provided. Unless otherwise indicated, photos are reprinted with
the permission of Commodore Business Machines. Use of the Commodore Madel
2022 printer was also provided by Commodore.
The
Digital Display Clock program listed in Chapter 5 is included courtesy of
Mr. Patrick
L. McGuire, Leland Enterprises, Oakland, California. The authors wish
to extend their appreciation ta Mr. McGuire for his contribution.
Thanks are also extended to Mr. Jim Butterfield of Toronto, Canada, for sa
readily sharing his
memory map information. Any errors in the memory map ta-
bles in this book remain. of course, the responsibility of the authors.
HOW THIS BOOK HAS BEEN PRINTED
Notice that the text in this book has been printed in boldface type and
lightface type. The boldface type is used to highlight the key points discussed in
this book. The
lightface type expands on information presented in the previous
boldface type. Therefore. read the
lightface type if you wish to know more about a
subject presented in boldface type.
xilï

CHAPTER 1
Introducing the PET
The Commodore PET is alow-cost personal computer housed in aself-
contained unit.
with keyboard, video display screen, and built-in or external mag-
netic tape cassette unit. The
PET is portable and can sit on adesk or tabletop.
Moreover, the
PET operates on normal household current and uses high quality,
but still inexpensive, magnetic tape cassettes to store information in acomputer-
readable form. The
PET is powered up simply by plugging it in and turning it on.
COMMUNICATING WITH THE PET
Whenever you power up the PET, Vou activate its BASIC· "in-
terpreter." The BASIC interpreter is acomputer program that is permanently
built into every PET. The PET BASIC interpreter carries out orders vou give it by
typing
in commands at the PET keyboard. It allows vou to start programming your
PET as soon as vou turn the power on.
You can command the PET to load aprogram from atape cassette, list the
program, execute the program, and perform anumber of related chores. You can
also type in your
own programs at the PET keyboard, edit them, run them, and
store them
on tape cassettes.
"BASIC is aregistered trademark of the Trustees of Dartmouth College.

ROM AND RAM
The BASIC interpreter is heId in atype of memory called "Read-Only
Memory" lotherwise known as ROM). ROM will keep its information
forever. whether electric power
is turned on or off. Read-Only Memory, and
the information it holds, thus becomes apermanent part of your PETs electronics.
THO' MOST PROC:rRAMS
AR~ BUT EPHEMERAE
,
YOU'LL EVER GRAC.E
MY READ-ONl V MEPtoRY!
ln contrast. aprogram loaded from atape cassette, or input from the
keyboard.
is placed into ReadlWrite Memory lotherwise known as RAM).
Any information stored
in RAM is lost when the PET's power is turned off.
That is why vou need acassette unit (or similardevice) ta store programs that Vou
want ta keep and use again and again.
2

BASIC PROGRAMMING
Ahost of pre-written programs is available on tape cassettes that vou
can load into memory
and execute simply by pressing acouple of keys on the
PET. Some of the programs
that vou can get are listed below. Some sources of
pre-written
PET programs are listed in Appendix E.
Address Book
Air-Sea War
Alphabetizing
Baseball
Battleship
Biorhythm
Blockade
Calendar
Checkbook
Check Writer
Chemistry Drills
Computer Art
Craps
Cryptograms
Depth Charge
Dogfight
Editor
ESP Test
Football
Foreign Language
Golf
Hangman
Home Accounting System
Hostage
Investment Analysis
Inventory
Kite Fight
Life
Lunar Lander
Maze
Memory Test
Othello
Personal Ledger
Poetry
Poker
Pong
Racetrack
Recipe File
Rhyming
Road Rally
Schedule Planner
Spelling
Star Trek
State Capitols
Stock Portfolio Analysis
Tic-tac-toe
Unlist
Vocabulary
Wallpaper
Wumpus
Yahtzee
ln addition to buying programs, Vou can also write your own programs
in the BASIC language, to be developed and executed on the PET.
"BASIC". Beginners Ali-purpose Symbolic Instruction Code. was developed
at Dartmouth College in 1963.
It is one of the most popular computer languages.
particularly favored by beginning programmers because it
is easy to learn and
easy to
use. PET BASIC is avariation of Dartmouth BASIC.
A
word of caution here: if vou have never programmed before. do not be
misled into thinking that with your personal computer vou will have your menus.
personal calendar. Esperanto concordance. and
FBI agent file ail safely stored and
working in afew hours! There are real limitations to the
PET -or any personal
computer -
as this book points out. Even with the best of languages and the
most expensive
of systems. writing useful. error-free programs is areal challenge.
But if vou have abent for programming. and vou
will have agood idea whether
vou do or not after reading this book. vou will find writing your own programs for
the
PET to be an exciting. rewarding pastime.
PET MODELS
The first PETs were available with acompact. custom graphies keyboard
and built-in tape cassette unit.
as shown in Figure 1-1 a. Additional PET models
are now available that have full-size keyboards. The tradeoff for these full-size
keyboards
is that the tape cassette unit must be connected externally. The full-
size "graphies" keyboard
is shown in Figure 1-1 b. The CBM (Commodore Busi-
ness Machinel. a
PET that has afull complement of small-business programs. and
that also functions
as a word processor. is shown in Figure l-1c.
3

b. PET with full-size graphies keyboard
a. PET with compact graphies keyboard
and built-in tape cassette
unit
c. CBM. or Business PET
4
Figure 1-1. Three Models of the Commodore PET

FEATURES
Ail PET models are housed in very similar cabinets and have asimilar set of
specifications, as listed in Appendix H. The only differences that vou need to be
concerned with in using this book are:
1. Whether your PET has the original ROMs. also ca lied "old" ROMs. which
are Revision Level 2; or the newer ROMs. which are Revision Level 3.
The newer ROMs eliminate problems that were encountered with the original
ROMs.
Vou have Revision 2ROMs if your
PET powers up with the first line printed as:
***COMMOOORE BASIC***
Vou have Revision 3ROMs if your PET powers up with the first line printed as:
###COMMOOORE BASIC###
If vou have the old ROMs, read carefully Appendix G, "Variations for Original
ROMs {Revision Level 2)," This appendix delineates every change vou
will
have to make, chapter by chapter, to use this book with the old ROMs. The
changes are not extensive. The rest of this book assumes that vou have the
newer ROMs.
2. Whether your PET has the compact keyboard or one of the full-size
keyboards. This book is written for ail PET keyboards, and differences, where
they
exist are clearly spelled out.
3. How much memory your PET has. Vour PET may have 4K, 8K, 16K, or 32K
bytes of memory. This
is Read/Write Memory (RAM): ail PETs have the same
amount of Read-Only Memory (ROM), A "K" is, roughly, one thousand A
"byte" is the standard unit of memory storage in the PET: each byte can ho Id
one character of data.
The more memory your PET has. the longer the programs and the larger
the amounts of data
it can handle at one time. However, this is not an opera-
tional difference and
is not important in learning how to use the PET. Vou only
need to
be aware of the memory size for the few references to the "top of memo-
ry," whose value
will depend on how much RAM is implemented in your PET.
5

CHAPTER 2
Operating the PET
This chapter tells vou how to operate the PET keyboard, use the screen dis-
play, and work
with the magnetic tape cassette drive. After reading this chapter,
vou
will be able to load and use pre-written PET programs stored on tape
cassettes.
The primary external features of the
PET are shown in Figures 2-1 and 2-2.
The Model 2001-8
in Figure 2-1 a has acompact keyboard and built-in tape
cassette unit. The 2001-16, 2001-32, and CSM models have front panels
as
shown in Figure 2-1 b with afull size keyboard and separate tape cassette unit.
The back view
is the same for ail units and is shown in Figure 2-2.
UNPACKING
Assuming vou have just brought your PET home in abox, vou must unpack
it. The PET is packed in protective material. inside aheavy-duty cardboard box. In-
spect the box for any evidence of shipping damage. Carefully open the box and
remove the
PET. Place the PET on asturdy, level surface su ch as atable or desk
top. Inspect the
unit for any evidence of shipping damage. Report any apparent
damage to the shipping agent. or to the dealer from
whom you purchased the
PET. Read any special material enclosed in the box; be sure to complete the war-
7