Table Of ContentUsing CP/M
Peter Gosling
M
MACMILLAN
© Peter Gosling 1985
All rights reserved. No reproduction, copy or transmission
ofthis publication may be made without written permission.
No paragraph ofthis publication may be reproduced, copied
or transmitted save with written permission or in accordance
with the provisions ofthe Copyright Act 1956 (as amended).
Any person who does any unauthorised act in relation to
this publication may be liable to criminal prosecution and
civil claims for damages.
First published 1985
Published by
MACMILLAN EDUCATION LTD
Houndmills, Basingstoke, Hampshire RG212XS
and London
Companies and representatives
throughout the world
British Library Cataloguing in Publication Data
Gosling, Peter
Using CP/M.
1. CP/M (Computer operating system)
2. Microcomputers
I. Title
001.64'25 QA76.6
ISBN 978-0-333-38403-9 ISBN 978-1-349-07676-5 (eBook)
DOI 10.1007/978-1-349-07676-5
Contents
Preface iv
1 What is CP/M? 1
2 Formatting a New Disk 5
3 CP/M Resident Commands 9
4 PIP, the Peripheral Interchange Program 14
5 The STAT Command 21
6 ED, the CP/M Line Editor 29
7 using MBASIC 42
8 Using a Compiler 58
9 ASM, the CP/M Assembler and DDT 69
10 CP/M Plus (CP/M Version 3.1) 86
11 CP/M-86 102
12 MP/M 107
13 Concurrent CP/M 111
14 CP/NET 114
Appendix A: ASCII Character Codes 119
Appendix B: CP/M Console Editing Commands 120
Appendix C: CP/M Packages 121
Index 123
Preface
This book i s intended t o give newcomers to the CP/M
operating system an insight into its capabilities and
method of use. So many microcomputers now use this
operating system that there i s a need for a simple yet
comprehensive guide to the many commands and functions
offered. Manuals supplied with computer systems are
notoriously difficult to follow even by the specialist,
l et alone the newcomer. This book aims at being as
general and non-specific as possible, since there are
many microcomputers on the market that consist of
extras added onto the main core of CP/M. It is to cover
this common core that this book has been writ ten.
The author would like to thank in particular Digital
Research (UK) Ltd for a mass of very useful information
and permission to reproduce certain diagrams in the
text. Help was also very gratefully received from
MidIand Micro Services and BurghIey Computers of
Stamford, and Stamford College for Further Education.
The addresses of Digital Research and the CP/M Users
Group for the UK are given in Appendix C.
PETER GOSLING
CP/M and CP/NET are registered trademarks of Digital
Research. CP/NOS, MP/M II and CP/M Plus are trademarks
of Digital Research.
Zilog and ZaD are trademarks of ZILOG Inc.
1 What CP/M?
IS
CP/M stands for "Control Program for Microcomputers",
or "Control Program and Monitor"; no-one now seems
quite certain exactly which of these is correct. It is
an operating system for the range of microcomputers
that have a Zilog Z80 - or look-alike - microchip as
their central processor.
The first CP/M operating system saw the light of day
in the early 1970s and was written by Dr Gary Kildall
who was one of the scientists behind the early
development of software for the Intel 8080
microprocessor.
As a multiplicity of disk drives (all of different
sizes and recording formats) came onto the market, it
rapidly became apparent that there was going to be no
future in designing a different operating system for
each set of peripherals attached to the computer. This
gave rise to the concept that gives CP/M its great
f 1exibi1i ty and portabi1i ty. The operating system
consists of three parts. These are called the BIOS, the
Basic Input and Output System, the BOOS, the Basic Disk
Operating System and the CCP which is the Console
Command Processor.
The BIOS is the only part of CP/M that is dependent
on the hardware. It is the non-proprietary part of the
operating system and can be modified by a microcomputer
manufacturer in order to cope with his particular
arrangement of disk drives, console VDU and printers. A
source listing of BIOS code is available from Digital
Research Inc.
The BOOS is a fixed, invariant and proprietary piece
of software which control s all the disk drives. It is
quite independent of the hardware being used.
The CCP is the software, also invariant and
proprietary, which translates the commands issued by
the user at the console keyboard into code ready for
the microprocessor to execute.
When CP/M is loaded into memory it is stored in
2 Using CP/M
segments with the BIOS at the highest par t of memory,
the BOOS just below it and the CCP below that. The bulk
of the remainder of memory is left for use by programs
and is called the TPA, the Transient Program Area. This
is the extent of memory that is addressable by a
running program. The amount of memory used up by the
BIOS depends on the hardware configuration and
typically would be around 3K bytes. BOOS, which is
always of constant size, occupies 3.5K bytes. This is
because, whatever the disk format in use, CP/M always
handles disk reading and writing in 128 byte blocks on
up to sixteen disk drives. The actual physical transfer
of data between disk and RAM is dealt with by the BIOS.
High Memory
BIOS
(up to 3K bytes)
BOOS
(3.5K bytes)
CCP
(2K bytes)
Transient
Program
Area
OlOOH
256 bytes reserved
OOOOH
Low Memory
What is CP/M? 3
Below the BIOS and BOOS lies the CCP and the TPA,
and right at the bottom of memory is a 256 byte block
holding the system parameters. It is through these that
the program being run communicates with the resident
CP/M utilities. This means that when a disk write
operation is initiated by your program the actual
writing is handed over to the BOOS and then to the BIOS
to execute the transfer of data. Incidentally, since
256 in hexadecimal is 100 this is the lowest address in
the TPA and is the starting address of many programs. A
typical memory map for CP/M is shown.
Part of CP/M, as can be seen from the memory map, is
always "resident" in memory. There are other
"transient" parts of the operating system which are
loaded f rom disk as required. These commands are
described in chapter 3.
When you switch on your microcomputer, the first
operation is to load CP/M into memory. This is called
"bootstrapping" or the system "booting" for short.
Sometimes this is initiated by pressing certain keys on
the console keyboard, sometimes it happens
automatically as soon as the system disk is inserted
and the drive door is closed. You can tell when the
loading is complete when some sort of "commercial"
appears on the screen followed by the familiar CP/M
A>
prompt. This tells us that the CCP is in operation and
that it is ready to respond to a command line.
If for some reason you need to restart your CP/M
system after having switched on the system, you can
perform a so-called "warm boot". This is often
necessary after an error has occurred and this error
has been indicated by one of CP/M's notorious error
messages. A warm boot is usually effected by pressing
CONTROL-C (that is, the CONTROL and C keys) What this
does is to reload the BOOS and CCP into memory and
place the computer into command mode.
A common CP/M error message is
Orive=nn,Track=nn,Sector=nn:Error=nn
Bdos error on X:bad sector
which indicates a hardware prob1em of some sort.
CONTROL-C will reboot the system and you can try again.
4 Using CP/M
If you press RETURN, the error is ignored and you are
returned to the CCP. The drive number, track number,
sector number and error code are all in hexadecimal.
All the error codes prefixed uy a 1 indicate that a
sector cannot be found. Codes prefixed by a 2 indicate
that a sector cannot be read. A 3 prefix tells us that
there is an error in verifying what is on the sector.
Finally a code prefixed with a 4 indicates a formatting
error.
Another i s
Bdos err on X:R/O
which tells us that the drive specified i s designated
read/only. Again CONTROL-C will return you to the CCP.
2 Formatting a New Disk
Before using any new disks on a CP/M system, or any
computer system for that matter, these disks have to be
"formatted". Formatting disks is the operation of
preparing them to have data recorded on them and it is
very similar to the operation of ruling lines to
provide blank columns in a ledger. Because every
computer system seems to have a different way of laying
out its disks, they cannot be supplied ready formatted
by the manufacturers. It is perhaps worth while at this
stage, before going into how disks are formatted, to
describe the layout of the disks used by typical
microcomputer systems. At present there are three kinds
of disk storage available: these are on 5-1/4 inch
diameter floppy disks, 8 inch diameter floppy disks and
the so-called "Winchester" or hard disks.
Each of the disk systems stores data magnetically on
a series of concentric tracks. The smallest disks can
store data on one or both sides and on either 40 or 80
tracks. The larger floppy disks can also be single or
double sided and usually store their data on 77
concentric tracks. To add to the confusion, the data
storage can be either at double or single density; this
refers to the amount of data that can be packed into
each track and is decided by the disk manufacturer. In
other words it is a measure of the "magnetisability" of
the magnetic substance that coats the plastic base of
which the disk is made. The Winchester drives consist
of more than one aluminium disk, coated with magnetic
material, mounted on a common spindle and hermetically
sealed into a box.
Each track of a disk is made up of a series of
"sectors" which can store a specified number of bytes,
or characters. In some cases the number of bytes per
sector and indeed the number of sectors per track can
be determined by the user although in general they are
decided by the manufacturer of the computer system. If
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