Commodore Plus/4 User manual

Programmer's Reference Guide for the
Commodore Plus /4
Cyndie Merten • Sarah Meyer

Programmer's
Reference Guide
for the
Conunodore Plus/4

Programmer's
Reference Guide
for the
Commodore Plus/4
Cyndie Merten
Sarah Meyer
SCOTT, FOKESMAKT AND COMPANY
Glenview, miaols London

Graphics characters that appear in Table 3-1 and Appendixes C and E are used with permission of Commodore
Business Machines, Inc.
Copyright © 1986 Cyndie Merten and Sarah Meyer.
All Rights Reserved.
Printed in the United States of America.
ISBN 0-673-18249-5
Library of Congress Cataloging-in-Publication Data
Merten, Cyndie.
Programmer's reference guide for the Commodore
Plus/4.
Includes index.
1. Commodore Plus/4 (Computer)—Programming.
2. BASIC (Computer program language) 1. Meyer, Sarah C.
II. Title.
QA76.8.C65M47 1986 005.2'65 85-18409
ISBN 0-673-18249-5
2 3 4 5 6-RRC-90 89 88 87 86
The following are trademarks of Commodore Business Machines, Inc.: Commodore and the Commodore
logo, Commodore Plus/4, Commodore 16, Commodore 64, VIC-20, VIC-1541, 1531 Datassette, C2N/1530
Datassette, Modem/300 Model 1660, MPS-801, Joystick T-1341, VIC-1526, VIC Modem 1600,
Automodem 1650. The following is a registered trademark of Parker Brothers: Boggle.
Notice of Liability
The information in this book is distributed on an "As Is" basis, without warranty. Neither the author nor
Scott, Foresman and Company shall have any liability to customer or any other person or entity with
respect to any liability, loss, or damage caused or alleged to be caused directly or indirectly by the programs
contained herein. This includes, but is not limited to, interruption of service, loss of data, loss of business or
anticipatory profits, or consequential damages from the use of the programs.

Preface
The Commodore Plus/4 represents an important advance in home computer
design. The low-priced Plus/4, which Commodore refers to as its productivity
computer, includes significant improvements over the phenomenally popular
Commodore 64 and over any other computer in the home computer class. The
built-in features include an expanded version of BASIC (Version 3.5), a machine-
language monitor, graphic-drawing commands, improved disk- and error-
handling commands, and integrated software that combines three programs:
A word processor
A spread sheet, with a graph generator linked to it
A file manager
The built-in programs are accessed by a function key.
The Plus/ 4 has 64 K RAM built in, 60671 bytes of which are available for use in
BASIC. The Plus/4 also has eight defined function keys that are easy to redefine
with the KEY command. Escape key functions simplify screen editing tasks and
let you create screen windows. The Plus/4 also has simple color settings that let
you select from 121 different hues. In addition, the graphics modes let you use the
drawing commands to draw pictures in high-resolution or multicolor modes. You
can also select split-screen graphics modes that display regular text in a five-line
screen window while the top of the screen is in a graphic mode. Graphic handling
is much easier in BASIC Version 3.5 than it is in the Version 2.0 built into the
Commodore 64.
Although the Plus/4 is superior to the Commodore 64, it does have one
disadvantage: a full library of software is not yet available for the Plus/4. In
addition, the Plus/4 does not have sprite graphics, which are available on the
Commodore 64, and the Plus/4 music features are not as sophisticated, although
music is easier to program.
When Commodore introduced the Plus/4, it was called the Commodore 264.
The name was changed to Plus/4 when Commodore decided to include the
built-in integrated software. At the time of the name change, Commodore also

vi Preface
announced the Commodore 16, which is compatible with the Plus/4. The Com
modore 16 has only 16 K RAM and no built-in software. The two new computers
are compatible, so all Commodore 16 software and peripherals are compatible
with the Plus/4.
About This Book
The Programmer's Reference Guide for the Commodore Plus/4 is a reference
book for programmers of all levels. The book provides information for both
BASIC and machine language programmers. The authors assume that readers
are familiar with the general operations of the Plus/4 and understand all the
keyboard functions. Neither BASIC nor machine language is taught in this book,
but extensive information is provided on programming in both languages. Pro
grammers of either BASIC or machine language will find the information they
need to write programs for themselves or for commercial distribution.
The authors have written and tested all the programs in this book. (Please note
that the programs are copyrighted and cannot be used for commercial purposes.)
Cyndie Merten, programmer and mathematician, is a founding member of
Dyadic Software Associates, a group of microcomputer consultants. Sarah
Meyer is a free-lance technical writer who has published another book about the
Plus/4. Together they have published several articles about Commodore comput
ers. The authors combine their perspectives as programmer and writer to produce
a book that is thorough, technically accurate, and clearly written. Please note that
Commodore Business Machines, Inc. has not been involved in the preparation of
this book. The authors bear responsibility for the accuracy of the material
presented here.
The Programmer's Reference Guide for the Commodore Plus/4 is divided into
six chapters. The chapters cover BASIC, the built-in software, programming
techniques, machine language, graphics, and peripheral devices. Memory maps
and other technical information are covered in the appendixes.
Chapter 1, The BASIC Language, provides complete descriptions of all 75+
commands, 36 functions, and the system variables that constitute BASIC 3.5. To
simplify looking up BASIC keywords, the elements of BASIC 3.5 are presented
in alphabetical order, with commands, functions, and system variables inter
mixed. For each keyword, the following information is given:
1. The abbreviation (when there is one).
2. A complete syntax, so you can quickly review the order of parameters.
3. A description of all uses for the command or function.
4. An explanation and range of possible values for each parameter.
5. Examples.

Preface vii
Graphics commands are given additional coverage in Chapter 4, Programming
Graphics. Commands for controlling peripherals are also discussed in Chapter 6,
Using Peripheral Devices. Chapter 3, Some Programming Techniques, also
provides more information on BASIC commands.
The commands for use in the built-in programs are explained in Chapter 2, The
Built-in Software. Chapter 2 is divided into four sections: word processor com
mands, commands for formatting printed output, spreadsheet commands
(including commands for controlling the graph generator), and file manager
commands. Within each section, commands are explained in alphabetical order.
Examples are given where appropriate.
Chapter 3, Some Programming Techniques, is a collection of sections on
diverse programming topics. Both BASIC and machine-language programming
techniques are discussed. Sections include coverage of the following topics:
Editing the screen
Using the Escape key screen-editing functions
Using screen windows
Using text strings
Redefining the function keys
Using mathematical functions
Programming sound and music
Using arrays
Error handling
Chapter 4, Programming Graphics, explains the operations of the graphics
modes in both BASIC and machine language. Color and screen control, drawing
commands, and animation are among the topics discussed in this chapter. Many
example programs are also provided.
Chapter 5, Machine Language on the Commodore Plus/4, explains the use of
the built-in monitor commands and the application of 6502 machine-language
programming on the Plus/4. This chapter does not teach machine language, but
it does review the instruction set and describe the operating system for machine
language programmers of all levels.
Chapter 6, Using Peripheral Devices, describes the operations of the disk drive,
cassette recorder, printers, modem, and joystick in BASIC and machine lan
guage. Each peripheral, and the commands that control it, is explained in a
separate section. Particular attention is given to disk-handling operations. Disk
operating system (DOS) error messages are explained in Appendix A.
The appendixes are provided to explain additional technical information and
to provide quick reference material. The six appendixes cover error messages for

viii Preface
BASIC and DOS errors, BASIC tokens, character string (CHR$) codes, ASCII
codes, screen display codes, a musical note chart, and memory and register maps.
The Programmer's Reference Guide for the Commodore Plus/4 also contains
an extensive index that is designed to make finding information in this book
quick and easy. We advise users to consult the index first when seeking specific
information.
The authors have taken great care to ensure accuracy and thoroughness in the
topics that are presented in this book. We cannot guarantee, however, that the
book is error free. We have tried to make the book easy to use and understand,
and we hope you find it helpful and instructive. We welcome your comments and
corrections.