ATOMIC THEORY AND PRACTICE
Contents
Introduction - 1
BASIC PROGRAMMING
Chapter 
1 - Start Here 3
2 - Calculating in BASIC 11
3 - Planning a Program 17
4 - Writing a BASIC Program 23
5 - Loops 33
6 - Subroutines 39
7 - Arrays and Vectors 45
8 - Strings 57
9 - Reading and Writing Data 67
10 - More Space and More Speed 73
11 - Advanced Graphics 79
12 - What to do if Baffled 91
ASSEMBLER PROGRAMMING
Chapter 
13 - Assembler Programming 95
14 - Jumps, Branches, and Loops 105
15 - Logical Operations, Shifts, and Rotates 111
16 - Addressing Modes and Registers 117
17 - Machine-Code in BASIC 123
REFERENCE SECTION
Chapter 
18 - ATOM Operating System 131
19 - Cassette Operating System 139
20 - BASIC Statements, Functions, and Commands 143
21 - BASlC Characters and Operators 155
22 - Extending the ATOM 161
23 - Mnemonic Assembler 171
24 - Assembler Mnemonics 181
25 - Operating System Routines and Addresses 191
26 - Syntax Definition 199
27 - Error Codes 205
Index - 211
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Introduction
This manual explains how to connect up the ATOM, and how to program it 
in BASIC or Assembler. The manual is arranged in three sections 
printed on different coloured paper. If you have never programmed 
before you should read the BASIC section, on plain paper, starting 
from Chapter 1; but be warned that you are setting off on an adventure 
which will require some changes of attitude towards computers. The 
only way to learn the art of programming is by practice, and so every 
section of this manual includes many example programs which illustrate 
the concepts being explained. These should be typed in and tried out, 
even if at first you do not fully understand how they work. By the end 
of chapter 4 you will be able to write your own programs for many 
different types of problem, and you may wish to stop there. The 
subsequent chapters, 5 to 12, deal with progressively more advanced
features of the ATOM's BASIC.
If you have already programmed in BASIC you may prefer to turn to 
chapters 20 and 21 in the reference section; these contain a complete 
summary of all the BASIC statements, functions, commands, and 
operators. You will be pleased to discover a number of extensions in 
ATOM BASIC that are not found in other BASICS.
If you want to learn to program in Assembler you should turn to 
the second section of the manual which is printed on coloured paper, 
and read from chapter 13 onwards. Readers experienced in Assembler 
programming can jump to chapter 23 in the reference section, which 
gives a concise description of the ATOM assembler.
The third section of the manual, printed on plain paper, is the 
reference section. It contains a summary of all the ATOM's facilities, 
a listing of the special addresses in the ATOM, and the error codes.
If you have a minimal ATOM you will be able to run all programs 
whose sizes are given as less than 512 bytes, or which are so short 
that no size is given. Longer programs will require additional memory, 
but many programs can be reduced in size by using the abbreviations 
explained in chapter 10.
Acknowledgements
The preparation of this manual would not have been possible without 
the continuous assistance of everyone at Acorn. In particular I am 
grateful to Roger Wilson for providing details of the operation of the 
BASIC interpreter, and for assistance with editing the source of this 
manual; to Nick Toop for explaining many details of the ATOM's 
circuitry; and to Laurence Hardwick for testing the example programs. 
I would also like to thank the many people who provided comments on 
previous drafts of the manual.
The following example programs were provided by Roger Wilson: 
Curve Stitching in a Square, Tower of Hanoi, Eight Queens, Prime 
Numbers, Arbitrary Precision Powers, Day of Week, Random Rectangles, 
and Renumber; and the following by Nick Toop: Simultaneous Equations, 
Encoder/Decoder, Three-Dimensional Plotting, and Saddle Curve.
The manual was prepared and edited on an Acorn System Three, and 
the final artwork was prepared using the Acorn Text Processing 
Package.
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CONNECTIONS TO ATOM

ATOM KEYBOARD

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