CP/M 80 Programmer’s Guide

This book is for people who want to learn how to program under the CP/M 80 Operating System. It is not a guide to using CP/M. Before reading it you should have some knowledge of programming using Z80 machine code and programming in a high level language such as BASIC. You should also have read a book on CP/M operating such as Using CP/M by Peter Gosling (Macmillan, 1985). The main part of the present book is meant to be read sequentially and, if you have little experience of machine code programming, this is the way that you should read it. If you are already an experienced programmer, you may want to 'dive' into the book at a particular point. In this case, you will find a list of keywords at the front of each chapter which will tell you what is covered within that chapter, and a more detailed summary at the end of most chapters. The appendixes are meant to be used for reference purposes. They include descriptions of BDOS functions, laid out in alphabetical order with a separate page for each function. A list of functions grouped under appropriate headings is also given. Examples in this book are written using Research Machines Ltd's Z80 macro assembler ZASM, mainly because it is a true Z80 assembler. However, with minor changes they can run under other assemblers such as Microsoft's M80. The main differences between ZASM and M80 are summarised in appendix F. To reviewers and Research Machines Ltd for their help. In particular, to Research Machines for their permission to use some of the information on program portability in chapter 3. CP/M and CP/NET are registered trademarks of Digital Research. Zilog and ZBO are trademarks of Zilog Inc. ProPascal is a registered trademark of Prospero Software. Microsoft BASIC is a registered trademark of Microsoft. ZASM is a registered trademark of Research Machines Ltd. Wordstar is a registered trademark of MicroPro International Corporation. This book describes how to write programs using the main versions of CP/M 80: CP/M 1.4 and CP/M 2.2. It does not describe the additional facilities of CP/M Plus 80 or Personal CP/M 80. However, the general principles apply to these as well and this book should be a useful introduction to CP/M before you look at either of these operating systems. Examples are given in Zilog Z80 machine code because most versions of CP/M 80 are used with Z80 processors. You should therefore have an understanding of Z80 machine code. Appendix E summarises the differences between the various versions of CP/M. For the present, all you need to understand is that CP/M is a control program, or operating system. ## How do your programs interface with CP/M 80? CP/M has a number of interfaces and these are shown in figure 1.2. The layers shown normally communicate with the next layer down; for example, your programs normally communicate with the BDOS. However, there are exceptions, and under special circumstances your programs may wish to communicate with lower layers. Front Matter....Pages i-x Introduction....Pages 1-7 Program Development....Pages 8-15 Design....Pages 16-21 Using Simple BDOS Functions....Pages 22-35 File Handling....Pages 36-61 Disc Operations....Pages 62-72 Debugging your Programs....Pages 73-81 Random Access Files....Pages 82-86 Using BDOS Functions from High Level Languages....Pages 87-91 Back Matter....Pages 92-161