Part no 405000
Issue no 2
Date July 1984
CARE AND MAINTENANCE
Exposure
Like all electronic equipment, the Electron should not be exposed to direct sunlight for long periods.
Servicing
All servicing should be done through an authorised dealer. There are no servicable parts inside either the Electron or the mains adapter, and opening either case will void the warranty.
The mains adapter
Note that your Electron Microcomputer does not have a separate on/off switch, so to switch it off unplug the mains adapter.
To switch the computer off briefly, you can remove the small plug on the right hand side of the case. However, the mains adapter should not be left plugged into the domestic 13A socket for long periods if the Electron is not being used.
There is a thermal fuse built into the mains adapter and if this blows, you will need to replace the adapter (please contact your local dealer). The Electron Microcomputer contains its own short circuit protection, so adapter failure is unlikely.
UNDER NO CIRCUMSTANCES should the mains adapter be replaced by a normal mains plug. The mains adapter contains a transformer which reduces the mains to a safe low voltage for input to the Electron.
AUTHOR'S NOTE: Wherever the letters BBC are mentioned in this book they refer to the British Broadcasting Corporation.
© Copyright Acorn Computers Limited 1983
Neither the whole or any part of the information in, or the product described in, this manual may be adapted or reproduced in any material form except with the prior written approval of Acorn Computers Limited (Acorn Computers).
The product described in this manual and products for us with it are subject to continuous development and improvement. All information of a technical nature and particulars of the product and its use (including the information and particulars in this manual) are given by Acorn Computers in good faith. However, it is acknowledged that there may be errors or omissions in this manual. A list of details of any amendments or revisions to this manual can be obtained upon request from Acorn Computers Technical Enquiries. Acorn Computers welcome comments and suggestions relating to the product and this manual.
All correspondence should be addressed to:
Technical Enquiries
Acorn Computers Limited
Fulbourn Road
Cherry Hinton
Cambridge CB1 4JN
All maintenance and service on this product must be carried out by Acorn Computers' authorized dealers. Acorn Computers can accept no liability whatsoever for any loss or damage caused by service or maintenance by unauthorised personnel. This manual is intended only to assist the reader in the use of the product, and therefore Acorn Computers shall not be liable for any loss or damage whatsoever arising from the use of any information or particulars in, or any error or omission in, this manual, or any incorrect use of the product.
First published 1983
Published by Acorn Computers Limited
Typeset by Bateman Typesetters, Cambridge
Contents
1 What is a computer? 1
2 Getting started 2
Checklist of items 2
Additional items 2
Connecting the Electron to your television set 2
Connecting the Electron to the mains 4
Tuning the TV to the Electron 4
Push-button tuning 4
Single tuning knob 5
Connecting the Electron to a monitor 5
Monochrome monitor 5
Colour (RGB) monitor 5
Now try something 5
3 Using a cassette recorder 7
Introduction 7
Connecting a cassette recorder 7
Motor control 8
4 The Introductory Cassette 9
Adjusting the volume control and loading the first program 9
Loading each program from the cassette 14
5 How to use the keyboard 16
Introduction 16
Choosing the keyboard characters 18
SHIFT and CAPS LK 18
SHIFT 18
FUNC 19
The arrow keys and the COPY key 19
What the arrow and COPY functions do 19
Summary 20
6 Introducing commands and programs 21
What is hexadecimal? 23
7 Editing programs 24
Introduction 24
Listing the program 25
Editing programs 26
Editing with the arrow keys and the COPY key 26
Deleting lines from your program 28
Inserting new lines into your program 29
Renumbering the program 30
Getting the computer to number each program line 31
Putting notes into your programs 32
Retrieving a program and starting a new one 32
Listing long programs 33
8 Trying out some programs 34
Introduction 34
PERSIAN 34
POLYGON 35
DRAW 36
9 Recording programs on cassette 38
Saving (recording) a program on cassette 38
Checking a recording 39
Loading a program from cassette 39
Cataloguing the tape 41
What the numbers mean 41
Escape 41
10 The FUNC key and BASIC keywords 42
11 Variables and expressions 44
What is a variable? 44
Real variables 44
Operators and expressions 45
Rules for variable names 46
Integer variables 47
A% to Z% 47
Real versus integer variables 48
DIV and MOD 48
The TIME integer variable 49
String variables 49
Commands operating on strings 51
LEN 51
Linking strings 52
LEFT$, RIGHT$, MID$ 52
VAL, EVAL, STR$ 53
INSTR 53
STRING$ 54
Comparison table of variables 54
12 Operator precedence 55
13 Arrays 56
14 READ...DATA...RESTORE 58
15 PRINT formatting and INPUT 59
PRINT formatting 59
INPUT 64
16 Conditional and loop instructions 68
The FOR . . . NEXT loop 66
The REPEAT . . . UNTIL loop 72
IF . . . THEN . . . ELSE 73
17 Procedures 77
Using parameters in procedures 81
18 GOTO and GOSUB 84
GOTO 84
GOSUB . . . RETURN 84
ON . . . GOTO, ON . . . GOSUB 86
19 Functions 87
20 Graphics 89
Introduction 89
Modes - what are they and why? 89
Writing text 90
The COLOUR command and text windows 90
Addresses on the text screen 90
Text windows 92
Defining your own characters 93
Graphics 95
Introduction 95
The graphics coordinate system 96
The GCOL command 97
The PLOT command 99
Advanced graphics 99
Triangle plotting 99
Sideways filling on background colour 99
Filling right 100
The VDU command 100
Graphics windows 101
The graphics origin 101
Plotting characters 102
The palette 102
21 VDU codes 104
Introduction 104
Detailed description 104
22 Making sounds 116
Introduction 116
The SOUND channel 116
The Q parameter 117
The A parameter 117
The P parameter 117
The D parameter 118
Using the SOUND command in a program 118
ENVELOPE 120
The ENVELOPE command 121
Constructing an ENVELOPE 121
Additional SOUND features 123
Example SOUND and ENVELOPE programs 125
23 Address pointers, indirection operators 127
The Electron's memory 127
Indirection operators 129
24 User-programmable keys 131
For the more advanced 131
25 BASIC keywords 133
BASIC keywords 134
26 Cassette file handling 195
27 Error handling 198
28 Merging BASIC programs 200
29 Assembly Language 202
Introduction 202
Registers in the 6502 203
Accumulator 203
Index registers X and Y 204
Program counter 204
Stack pointer 204
Flags register 205
Addressing modes 206
Entering assembly mnemonics 210
Assembly 211
Execution by USR 214
Execution by CALL 214
Quadruple precision addition 220
Multiplication 221
Division 225
Error trapping in assembler 227
Operating system calls from assembler 228
Use of operating system calls 230
OSWRCH entry: &FFEE vector: &20E 230
OSASCI entry: &FFE3 232
OSNEWL entry: &FFE7 232
OSRDCH entry: &FFE0 vector: &210 233
OSCLI entry: &FFF7 vector: &208 234
OSFIND entry: &FFCE vector: &21C 234
OSBPUT entry: &FFD4 vector: &218 234
OSBGET entry: &FFD7 vector: &216 234
OSFILE entry: &FFDD vector: &212 234
OSBYTE entry: &FFF4 vector: &20A 235
OSWORD entry: &FFF1 vector: &20C 238
Events 242
Assembly Language mnemonics 243
Appendix A
VDU codes 265
Appendix B
Error messages 269
Appendix C
Operating system calls 278
Appendix D
*FX calls 280
Appendix E
Fast and efficient programs 284
Appendix F
ASCII displayed character set and control codes 285
Appendix G
Text and graphic planning sheets 287
A computer is a general purpose electronic machine that can be instructed to do a great variety of things - play games, perform complex calculations, store and retrieve information, display graphs and so on.
You can ask a computer to do things directly - by typing commands on its keyboard - but for complex tasks, a whole series of instructions is usually written and stored in the computer's memory. The computer can be instructed to call up these instructions one by one and carry them out, very fast. (Your Electron can carry out, or 'execute', over 250,000 separate instructions every second.)
A series of instructions like this is called a program. Programs can be recorded onto cassette by using a suitable cassette recorder in much the same way as you might record a piece of music. The main difference is that the recording is made from a computer, and is played back into the computer again. You can buy pre-recorded programs which have been written by other people, and to start you off, several programs are provided on the Introductory Cassette which comes with your Electron.
The first part of this book describes how to set up your computer, and load and run the programs on the Introductory Cassette. For information on other programs available for the Electron (the general name for programs is 'software'), write to:
Acornsoft Limited
4a Market Hill
Cambridge CB2 3NJ
The remainder of this book (chapter 4 onwards), and the book Start Programming with the Electron, will tell you how to write your own programs on your Electron computer. You do not need to know this in order to use your computer, as there are many commercially available programs - but we hope that you will be interested and will want to find out more about your Electron.