Commodore VIC-20 User manual

VIC 20·
John Hellborn
Ran Talbott
Osborne/McGraw-Hill
Berkeley, California
User
Guide
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+'ll(C~

Disclaimer of Warranties and Limitation of Liabilities
The authors have taken due care in preparing this book and the programs in it, including
res'earch, development, and testing
to ascertain their effectiveness. The authors and the
publisher make no expressed or implied warranty ofany kind with regard
to these pro-
grams or the supplementary documentation in this book. In no event shall the authors or
the publisher be liable for incidental
or consequential damages in connection with or aris-
ing out of the furnishing, performance,
or use ofany ofthese programs.
VIC
20 is a trademark of Commodore Business Machines, Inc. The VIC 20™ User Guide
is not sponsored or approved by or connected with Commodore Business Machines, Inc.
Commodore Business Machines, Inc. makes no warranty, express or implied, ofany kind
with regard to the information contained herein, its accuracy, or completeness.
Table
1-3 (1540 Disk Drive Specifications) is reprinted by permission ofCommodore
Business Machines, Inc. from the
1540 Commodore User Manual.
Table 1-4 (1515 Printer Specifications) is reprinted by permission of Commodore Business
Machines, Inc. from the
1515 Commodore User Manual.
Table B-1 (Memory Map) and Table B-4 (Kernal Memory Locations) are reprinted by
permission from the Programmer's Reference Guide, 2nd Edition,
1982, Commodore
Business Machines, Inc.
Figure C-I (Game port pinout), Figure C-2 (Expansion port pinout), Figure C-3 (Video
port pinout), Figure C-4 (Serial
I/O port pinout), Table D-2 (Conversion Values), Table
E-I (VIC Character Codes), Table E-2 (Screen Codes), Table
E-3 (VIC Character Codes),
and Table
E-5 (Keyword Abbreviations) are reprinted by permission from Personal Com-
puting on the VIC
20, 5th Edition, 1982, Commodore Business Machines, Inc.
Published by
OsbornejMcGraw-Hill
2600 Tenth Street
Berkeley, California
94710
U.S.A.
For information on translations and book distributors outside of the
U.S.A., please write to Osborne/McGraw-Hill
at the above address.
VIC 20™ USER GUIDE
Copyright @ 1983 by McGraw-Hill, Inc. All rights reserved. Printed in the United States
of America. Except as permitted under the Copyright
Act of 1976, no part of this publica-
tion may be reproduced or distributed in any form
or by any means, or stored in a data
base
or retrieval system, without the prior written permission ofthe publisher, with the
exception that the program listings may
be entered, stored, and executed in a computer
system, but they may not be reproduced for publication.
1234567890 DODO
89876543
ISBN 0-931988-86-1
Cover illustration by Hitoshi Matsuda
Cover design by Yashi Okita
Text design
by KLT van Genderen
Unless otherwise mentioned, all photos by Richard Cash

The authors dedicate this book to Christine Dec and
Sharon Hobson Heilborn, whose love arid support have meant
.more than these
few words can ever express.
·,
.._.--J

Contents
Acknowledgments Vll
Introduction ix
1 Introducing the VIC 20 Computer 1
2 Operating the VIC 20 39
3 Programming the VIC 20 Computer 57
4 Advanced BASIC Programming 117
5 Game Controllers 157
6 Graphics 171
7 Sound 227
8 Peripheral Devices 249
A System Architecture 293
B Memory Usage 295
C VIC I/O Pinouts 311
D Conversion Tables/Trigonometric Functions 317
E Sound and Display Characters and Codes 325
F Error Messages 335
G BASIC Statements 341
H BASIC Functions 371
Index 385
v

ACKNOWlIDGMENTS
No book is ever the work of just the authors and, of course, this book
is no exception. We would like to express our thanks to the following
people without whose help this work would never have become a reality:
Michael Tomczyk, whose enthusiasm and insight during a brief meet-
ing in Santa Clara got the whole thing started.
Bill Hindorff, whose technical assistance helped clarify many
of the
lesser known aspects
of the VIC 20.
Larry Ercolino, who provided a first-hand encounter in VICommuni-
cations and a seemingly never-ending supply
of support and information.
There were many others who also provided help when we needed it
the most, and often
at times that were quite inconvenient. Some of these
are
Pat McAllister, Jeff Hand, Andy Finkel, Neil Harris, Steve Murri,
Steven Moser, and
John Stockman.
Finally,
we wish to express our thanks to Denise Penrose whose
editorial guidance was invaluable in helping us complete this book.
JH
RT

I ntrod uction
The VIC 20 is a remarkablecomputer. Despite its low price and small
size, ithasmorefeatures thanlargerandmoreexpensivecomputersdideven
a
few years ago.
If you want to solve math problems, the VIC can run them for you. If
you need to type letters or mailing lists, the VIC will do the job quickly and
easily.
But in addition
to these functions, common to most computers, the
VIC offers color text and graphics.
Furthermore, the VIC
20 can produce tones within a range of nine
octaves. These can be combined to imitate anythingfrom the patter
of rain
to a cannonade.
Chapter 1 explains how
to unpack and set up the VIC 20 and its
accessories.
It contains a description of all the controls on the VIC, from
connectors to keyboard functions. .
Chapter 2 guides you through the VIC screen editor and explains the
two operating modes
of the VIC: immediate mode and programmed mode.
This
is followed by an introduction to the Datassette, the 1540 disk drive,
and the
1515 printer.
Chapter3introduces you toprogramming. All the BASICinstructions
are covered as well as the concepts
of loops, branching, Boolean operators,
Ix
I
- -'"

X The VIC 20 User Guide
floating point versus integer numbers, and scientific notation. The chapter
also describes variable types and the construction ofarrays.
Advanced BASIC programming
is the subject of Chapter 4. It will
teach you practical applications ofconcepts covered in Chapter
3. You will
learn how to write screen display programs, include cursor movement and
string variables as commands in your programs, and develop easy-to-use
110 intensive programs requiring considerable data entry. Chapter 4 also
discusses the VIC 20's real time clock and random number generator.
Chapter5
is a tutorial ongame controllers. It will show you how to use
the keyboard
as a game controller and how to write programs that access a
joystick or paddle controller.
Chapter 6 covers graphics.
It explains how the video display works,
how colors are produced, and how to putcharacters onthe screen. You will
learn how to animate pictures and produce high-resolution graphics using
BASIC.
Chapter 7 discusses sound generation on the VIC including the VIC
sound registers, the components
of sound, and how to use them. You will
learn how to program music into the VIC
20 and how to save it for playback
later on.
Chapter 8 explains the operation
of the major VIC peripherals: the
Datassette,
1540 disk drive, and 1515 printer. Itcontainsa complete discus-
sion ofdata
file creation, programstorage, and high-level disk operations. It
also discusses all the printer commands including double width characters,
reverse printing, and high-resolution graphics.
The appendixes contain tables on all the details discussed in the text,
from the systemarchitectureand blockdiagrams to the memory maps. You
will also find diagrams showing pinouts for all ofthe connectors as
well as
color, screen, and sound value tables.
* * *
As the electronic industry continues to grow at an incredible rate,
manufacturers are constantly introducing new equipment. Some
of these
products are
new; others are designed to replace existing equipment.
Two that were released when this book was being written are the
1525
printer and the 1541 disk drive.

Introduction xl
The 1525 printer is essentially an upgrade of the 1515 printer. It
operates like the 1515 and interfaces to the VIC in the same way. The major
differences are its slightly improved operation resulting from new internal
software and its redesigned case
that allows it to accept standard 9-inch
(including perforations) paper.
The
1541 disk drive was introduced to provide compatibility between
the VIC
20 and Commodore 64 computers. If you are using the VIC 20
alone, youcanuse eitherdiskdrive. ExceptJorthis compatibilitydifference,
the two disk drives are identical.
All the informationin this bookapplies to both new and old units ofthe
1515/1525 printers and the 1540/1541 disk drives.

CHAPTER
Introducing the
VIC 20 Computer
When you first unpack the VIC 20, you will find the equipment
'shown in Figure
1-1:
· The VIC 20 computer
• Television
RF modulator (small black box)
• Power supply (larger plastic box)
·
TV switch box
· Video cable
While your system may include additional components, all systems
include this basic equipment. This chapter identifies each component and
connector provided by Commodore and introduces the function ofeach.
Place the VIC
20 on a flat surface such as a table. Make sure that you
have room
to put a television near the VIC 20, ideally directly behind it.
REAR AND SIDE PANEL
All of the switches, connectors, and interfaces are located at the side
and back
ofthe VIC 20 computer. These components are labeled in Figure
1-2. It is important that you learn the function and location of each
1

2 The VIC 20 User Guide
FIGURE i-i. Equipment packed with the VIC 20
FIGURE 1-2. Rear/side view of the VIC 20
component as you hook up the computer to avoid damaging it by using
connections incorrectly.
Power SWitch
Makesure the VIC 20 is OFF at this point. The powerswitch is located
on the right side
of the computer. It is a two-position "rocker" switch.

Chapter 1. Introducing the VIC 20 Computer 3
When you turnthe powerswitch ON, the VIC will displaya dark screen
for a short time. During this period it
is initializing itself; that is, it is
checking out its internalsystems and determining how much memoryit has
available.
When you
turn the power OFF, all programs and data in memory that
were
not stored onto either diskette or tape will be lost.
Power Connector
The power supply has two cables attached to it. One plugs into any
standard
110 volt AC outlet. The other plugs directly into the power
connector next to the
ON/OFF switch on the side ofthe VIC 20.
Game Port
This connector is used for the various game controllers available for
the VIC 20, as well asfor the light penand somespecialapplicationdevices.
ATARIjoysticksand paddleswill work withthis port,as wellas those made
by Commodore.
Parallel User Port
The paralleluser port is a connectorthatallows you to hook up devices
(such as the VIC modem) to the VIC
20.
More advanced users may use this connectorfor custom applications
as well, since the signals coming from it can be programmed directly by the
VIC
20.
cassette Interface
The cassette interface is used to connect the Datassette, which is a
special digital tape recorder. You can use it to store
and reload programs
and
data into the VIC 20. The Datassette is described later in this chapter.
Serial Port
The serial port is used to connect the computer to the model 1515
printer, the disk drive, and other devices using a serial input/ output

4 The VIC 20 User Guide
configuration. Instructions for connecting the printer and disk drive to the
VIC
20 are provided later in this chapter.
Video Port
The VIC 20 produces the sound and pictures displayed on your
television by combining them into a signal called composite video. This
signal
is sent out through the video port.
A video monitor (a television without a tuner)
is able to convert the
composite video directly into pictures and sound. A television, however,
must be tuned to a particular channel. That signal
is produced and
combined with the compositevideo by the
RF (radiofrequency) modulator
(the small black box in Figure
1-1).
When you use the VIC 20 you can select either channel 3 or channel 4
by flipping the channel switch on the side of the modulator.
Expansion Interface
The expansion interface gives you access to the computer's memory
lines. Through it you may increase the memory size of your VIC
20 to as
much as 32K (more than 32,000 bytes).
NOTE: Increasingthe memorysize may cause the computer's memory
to be reconfigured. This will cause thescreen displayinformationand some
parts ofuser memory to
be moved to otherlocationsinmemory. Generally,
this will cause no noticeable changes.
In some cases, however, it will cause
program run failures. Look
at the memory map in Appendix Bfor specific
information on memory expansion and reconfiguration.
Video Display
When you first power up the VIC 20 it displays 23 rows with 22
characters perrow. The computergenerates these characters by lightingthe
appropriate pattern
of dots within an 8 X 8 matrix. This is illustrated in
Figure
1-3. The VIC 20's character set is quite extensive, containing 256
letters, numbers, and symbols. It is also possible to program custom
characters for special applications. This
will be discussed in Chapter 6.

Chapter 1: Introducing the VIC 20 Computer 5
•••
a. 8 X 8 dot matrix
b. Sample ietter A c. Sample Graphic
FIGURE 1·3. The 8 X 8 dot matrix
POWER UP
Connect the TV switch box to the back of the television by attaching
one end of the cable with the phono jacks (Figure
1-4) to the switch box.
FIGURE 1-4. Television switch box and connections

6 The VIC 20 User Guide
Connect the larger plug of the video cable to the round five-pin video
port on the back of the VIC
20 (see Figure 1-2).
Finally, plug the power supply cord into the VIC 20 powerconnector.
Do not turn on the VIC yet!
To start using your VIC 20, follow these steps:
1. Plug the AC power cord into a wall outlet.
2. Switch the power ON. The power switch is located onthe right side
near the AC plug.
3. Wait for the READY display. This can take several seconds,
duringwhich the VIC
is goingthrougha self-checkingandinitializa-
tion process.
The following display should now appear:
If you not not get this display, turn the power OFF, wait about ten
seconds, and turn the power ON again.
If you still don't get this display,
check the connections.
If that does not help, contact your Commodore
dealer.