introduction to Digital Systems This Page Intentionally Left Blank I n t r o d u c t i o n to Dig i ta / Systern s John Crisp Newnes OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE Newnes An Imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 2000 Transferred to digital printing 2004 © Iohn Crisp 2000 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England Wl P 9HE. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 4583 0 Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress p L T A m FOR BVI~ ~ "i"UATW E PtlBUSH, ISUT'ITImOlfI'H-HBI~JMANN ......W ILl, PAT I~M BTCV TO PLANT AND ~ FOIl A II'IIEI~, Composition by Genesis Typesetting, Rochester, Kent Contents Preface V°I, I 1 It's a digital world 2 it's numbers that count 3 Binary arithmetic 16 4 Hex to its friends 27 5 Just logic 39 6 Build your own gates 59 7 Designing digital circuits 69 8 Simplifying-by Boolean algebra 86 9 Simplifying- by Karnaugh maps 103 10 Real gates and their families 124 11 Interfacing 141 12 Sequential logic 155 13 Clocked bistables 167 14 Asynchronous counters 177 15 Synchronous and integrated counters 192 16 Some more counters, codes and registers 206 17 Digital devices 220 18 Transmission of digital data 243 ¥ Contents 19 Data on the move 252 20 Methods and measurements 269 21 Avoiding some problems- and finding the others 279 Quiz time answers 289 Further reading 292 Index 293 vl Preface Modern life depends on a few basic requirements and of these, one of the most important is digital electronics. In fact, it is difficult to imagine what would still be available to us if digital systems were removed. We would lose our computers, telephones, televisions, radios, CDs and microwave ovens. Our transport system could not include modern ships, aircraft, trains and even many cars. As the days pass, we become more dependent on digital systems. On our planet digital devices outnumber us by more than a billion to one! It's a good job they are friendly. The purpose of this book is to give a worry-free introduction to the world of digital electronics, tt starts at the beginning and does not assume any previous knowledge of the subject, and new topics are fully explained as they are introduced. John Crisp vii This Page Intentionally Left Blank It's a digital w o r l d In the year 49974 we could be in for a surprise- we may make our first contact with advanced aliens from deep space. In 1974, from the mountains of Puerto Rico, we launched a greetings card towards a group of 300000 stars. As you read this, our digital message is out there, about 250 million, million kilometres away, reaching out at the speed of light. Here is the message that we sent: 00(00010011 llllllOllll 01111000011 00011000011 Our amazingly intelligent neighbours will, of course, immediately realize that it is our address as shown in Figure 1.1. // -mill," Figure 1.1 iiii Our interstellar address This is obviously(?) a diagram of our solar system indicating that we inhabit the third planet