1. Digital SystemsPrinciples and ApplicationsRonald J. TocciMonroe Community CollegeNeal S.WidmerPurdue UniversityGregory L. MossPurdue UniversityTENTH EDITIONPearson Education International

2. If you purchased this book within the United States or Canada you should be aware thatit has been wrongfully imported without the approval of the Publisher or the Author.Director of Development:Vern AnthonyEditorial Assistant: Lara DimmickProduction Editor: Stephen C. RobbProduction Coordination: Peggy Hood,TechBooks/GTSDesign Coordinator: Diane Y. ErnsbergerCover Designer: Jason MooreCover Art: Getty OneProduction Manager: Matt OttenwellerMarketing Manager: Ben LeonardThis book was set in TimesEuropa Roman by TechBooks/GTSYork, PA Campus. It wasprinted and bound by Courier Kendallville, Inc.The cover was printed by PhoenixColor Corp.MultiSIM is a trademark of Electronics Workbench.Altera is a trademark and service mark of Altera Corporation in the United States andother countries. Altera products are the intellectual property of Altera Corporation andare protected by copyright laws and one or more U.S. and foreign patents and patent ap-plications.Copyright 2007 by Pearson Education, Inc., Upper Saddle River, New Jersey 07458.Pearson Prentice Hall. All rights reserved. Printed in the United States of America.Thispublication is protected by Copyright and permission should be obtained from the pub-lisherprior to any prohibited reproduction, storage in a retrieval system, or transmissionin any form or by any means, electronic, mechanical, photocopying, recording, or likewise.For information regarding permission(s), write to: Rights and Permissions Department.Pearson Prentice Hall is a trademark of Pearson Education, Inc.Pearson is a registered trademark of Pearson plcPrentice Hall is a registered trademark of Pearson Education, Inc.Pearson Education Ltd. Pearson Education Australia Pty. LimitedPearson Education Singapore, Pte. Ltd. Pearson Education North Asia Ltd.Pearson Education Canada, Ltd. Pearson Educacin de Mexico, S.A. de C.V.Pearson EducationJapan Pearson Education Malaysia, Pte. Ltd.Pearson Education, Upper Saddle River,New Jersey10 9 8 7 6 5 4 3 2 1ISBN: 0-13-173969-7 3. Digital SystemsPrinciples and Applications 4. Digital SystemsPrinciples and ApplicationsRonald J. TocciMonroe Community CollegeNeal S.WidmerPurdue UniversityGregory L. MossPurdue UniversityTENTH EDITIONUpper Saddle River, New JerseyColumbus, Ohio 5. Library of Congress Cataloging-in-Publication DataTocci, Ronald J.Digital systems : principles and applications / Ronald J.Tocci, Neal S.Widmer, Gregory L. Moss.10th ed.p. cm.Includes bibliographical references and index.ISBN 0-13-172579-31. Digital electronicsTextbooks. I. Widmer, Neal S. II. Moss, Gregory L.III. Title.TK7868.D5T62 2007621.381dc222005035835Director of Development:Vern AnthonyEditorial Assistant: Lara DimmickProduction Editor: Stephen C. RobbProduction Coordination: Peggy Hood, TechBooks/GTSDesign Coordinator: Diane Y. ErnsbergerCover Designer: Jason MooreCover Art: Getty OneProduction Manager: Matt OttenwellerMarketing Manager: Ben LeonardThis book was set in TimesEuropa Roman by TechBooks/GTSYork, PA Campus. It wasprinted and bound by Courier Kendallville, Inc. The cover was printed by PhoenixColor Corp.MultiSIM is a trademark of Electronics Workbench.Altera is a trademark and service mark of Altera Corporation in the United States andother countries. Altera products are the intellectual property of Altera Corporation andare protected by copyright laws and one or more U.S. and foreign patents and patent ap-plications.Copyright 2007, 2004, 2001, 1998, 1995, 1991, 1988, 1985, 1980, 1970 by PearsonEducation, Inc., Upper Saddle River, New Jersey 07458. Pearson Prentice Hall. All rightsreserved. Printed in the United States of America. This publication is protected byCopyright and permission should be obtained from the publisher prior to any prohibitedreproduction, storage in a retrieval system, or transmission in any form or by any means,electronic, mechanical, photocopying, recording, or likewise. For information regardingpermission(s), write to: Rights and Permissions Department.Pearson Prentice Hall is a trademark of Pearson Education, Inc.Pearson is a registered trademark of Pearson plcPrentice Hall is a registered trademark of Pearson Education, Inc.Pearson Education Ltd. Pearson Education Australia Pty. LimitedPearson Education Singapore, Pte. Ltd. Pearson Education North Asia Ltd.Pearson Education Canada, Ltd. Pearson Educacin de Mexico, S.A. de C.V.Pearson EducationJapan Pearson Education Malaysia, Pte. Ltd.10 9 8 7 6 5 4 3 2 1ISBN: 0-13-172579-3 6. To you, Cap, for loving me for so long; and for the millionand one ways you brighten the lives of everyone you touch.RJTTo my wife, Kris, and our children, John, Brad, Blake,Matt, and Katie: the lenders of their rights to my time andattention that this revision might be accomplished.NSWTo my family, Marita, David, and Ryan.GLM 7. viiPREFACEThis book is a comprehensive study of the principles and techniques of mod-erndigital systems. It teaches the fundamental principles of digital systemsand covers thoroughly both traditional and modern methods of applying dig-italdesign and development techniques, including how to manage a systems-levelproject.The book is intended for use in two- and four-year programs intechnology, engineering, and computer science. Although a background inbasic electronics is helpful, most of the material requires no electronicstraining. Portions of the text that use electronics concepts can be skippedwithout adversely affecting the comprehension of the logic principles.General ImprovementsThe tenth edition of Digital Systems reflects the authors views of thedirection of modern digital electronics. In industry today, we see the impor-tanceof getting a product to market very quickly.The use of modern designtools, CPLDs, and FPGAs allows engineers to progress from concept to func-tionalsilicon very quickly. Microcontrollers have taken over many applica-tionsthat once were implemented by digital circuits, and DSP has beenused to replace many analog circuits. It is amazing that microcontrollers,DSP, and all the necessary glue logic can now be consolidated onto a singleFPGA using a hardware description language with advanced developmenttools. Todays students must be exposed to these modern tools, even in anintroductory course. It is every educators responsibility to find the bestway to prepare graduates for the work they will encounter in their profes-sionallives.The standard SSI and MSI parts that have served as bricks and mortarin the building of digital systems for nearly 40 years are now nearing obso-lescence.Many of the techniques that have been taught over that time havefocused on optimizing circuits that are built from these outmoded devices.The topics that are uniquely suited to applying the old technology but do notcontribute to an understanding of the new technology must be removed from 8. viii PREFACEthe curriculum. From an educational standpoint, however, these small ICs dooffer a way to study simple digital circuits, and the wiring of circuits usingbreadboards is a valuable pedagogic exercise.They help to solidify conceptssuch as binary inputs and outputs, physical device operation, and practicallimitations, using a very simple platform. Consequently, we have chosen tocontinue to introduce the conceptual descriptions of digital circuits and tooffer examples using conventional standard logic parts. For instructors whocontinue to teach the fundamentals using SSI and MSI circuits, this editionretains those qualities that have made the text so widely accepted in thepast. Many hardware design tools even provide an easy-to-use design entrytechnique that will employ the functionality of conventional standard partswith the flexibility of programmable logic devices. A digital design can bedescribed using a schematic drawing with pre-created building blocks thatare equivalent to conventional standard parts, which can be compiled andthen programmed directly into a target PLD with the added capability ofeasily simulating the design within the same development tool.We believe that graduates will actually apply the concepts presented inthis book using higher-level description methods and more complex program-mabledevices.The major shift in the field is a greater need to understand thedescription methods, rather than focusing on the architecture of an actual de-vice.Software tools have evolved to the point where there is little need for con-cernabout the inner workings of the hardware but much more need to focuson what goes in, what comes out, and how the designer can describe what thedevice is supposed to do.We also believe that graduates will be involved withprojects using state-of-the-art design tools and hardware solutions.This book offers a strategic advantage for teaching the vital new topicof hardware description languages to beginners in the digital field.VHDL isundisputedly an industry standard language at this time, but it is also verycomplex and has a steep learning curve. Beginning students are often dis-couragedby the rigorous requirements of various data types, and they strug-glewith understanding edge-triggered events in VHDL. Fortunately, Alteraoffers AHDL, a less demanding language that uses the same basic conceptsas VHDL but is much easier for beginners to master. So, instructors can optto use AHDL to teach introductory students or VHDL for more advancedclasses. This edition offers more than 40 AHDL examples, more than 40VHDL examples, and many examples of simulation testing. All of these designfiles are available on the enclosed CD-ROM.Alteras latest software development system is Quartus II. The MAXPLUS II software that has been used for many years is still popular in indus-tryand is supported by Altera. Its main drawback is that it does not programthe latest devices. The material in this text does not attempt to teach a par-ticularhardware platform or the details of using a software development sys-tem.New revisions of software tools appear so frequently that a textbookcannot remain current if it tries to describe all of the details.We have triedto show what this tool can do, rather than train the reader how to use it. How-ever,tutorials have been included on the accompanying CD-ROM that makeit easy to learn either software package.The AHDL and VHDL examples arecompatible with either Quartus or MAXPLUS systems. The timing simula-tionswere developed using MAXPLUS but can also be done with Quartus.Many laboratory hardware options are available to users of this book. Anumber of CPLD and FPGA development boards are available for studentsto use in the laboratory. There are several earlier generation boards similarto Alteras UP2 that contain MAX7000 family CPLDs. A more recent exampleof an available board is the UP3 board from Alteras university program (seeFigure P-l), which contains a larger FPGA from the Cyclone family. An even 9. PREFACE ixnewer board from Altera is called the DE2 board (see Figure P-2), which hasa powerful new 672-pin Cyclone II FPGA and a number of basic features suchas switches, LEDs, and displays as well as many additional features for moreadvanced projects. More development boards are entering the market everyyear, and many are becoming very affordable.These boards, along with pow-erfuleducational software, offer an excellent way to teach and demonstratethe practical implementation of the concepts presented in this text.The most significant improvements in the tenth edition are found in Chap-ter7. Although asynchronous (ripple) counters provide a good introduction tosequential circuits, the real world uses synchronous counter circuits. Chapter7 and subsequent examples have been rewritten to emphasize synchronouscounter ICs and include techniques for analysis, cascading, and using HDL todescribe them. A section has also been added to improve the coverage of statemachines and the HDL features used to describe them. Other improvementsinclude analysis techniques for combinational circuits, expanded coverage of555 timer applications, and better coverage of signed binary numbers.FIGURE P-1 Alteras UP3development board.FIGURE P-2 Alteras DE2development board. 10. x PREFACEOur approach to HDL and PLDs gives instructors several options:1. The HDL material can be skipped entirely without affecting thecontinuity of the text.2. HDL can be taught as a separate topic by skipping the materialinitially and then going back to the last sections of Chapters 3, 4, 5,6, 7, and 9 and then covering Chapter 10.3. HDL and the use of PLDs can be covered as the course unfoldschapter by chapterand woven into the fabric of the lecture/labexperience.Among all specific hardware description languages, VHDL is clearly theindustry standard and is most likely to be used by graduates in their careers.We have always felt that it is a bold proposition, however, to try to teach VHDLin an introductory course.The nature of the syntax, the subtle distinctions inobject types, and the higher levels of abstraction can pose obstacles for abeginner. For this reason, we have included Alteras AHDL as the recom-mendedintroductory language for freshman courses.We have also includedVHDL as the recommended language for more advanced classes or introduc-torycourses offered to more mature students.We do not recommend trying tocover both languages in the same course. Sections of the text that cover thespecifics of a language are clearly designated with a color bar in the margin.The HDL code figures are set in a color to match the color-coded text expla-nation.The reader can focus only on the language of his or her choice and skipthe other. Obviously, we have attempted to appeal to the diverse interests ofour market, but we believe we have created a book that can be used in multi-plecourses and will serve as an excellent reference after graduation.Chapter OrganizationIt is a rare instructor who uses the chapters of a textbook in the sequence inwhich they are presented. This book was written so that, for the most part,each chapter builds on previous material, but it is possible to alter the chap-tersequence somewhat. The first part of Chapter 6 (arithmetic operations)can be covered right after Chapter 2 (number systems), although this will leadto a long interval before the arithmetic circuits of Chapter 6 are encountered.Much of the material in Chapter 8 (IC characteristics) can be covered earlier(e.g., after Chapter 4 or 5) without creating any serious problems.This book can be used either in a one-term course or in a two-term se-quence.In a one-term course, limits on available class hours might requireomitting some topics. Obviously, the choice of deletions will depend on fac-torssuch as program or course objectives and student background. A list ofsections and chapters that can be deleted with minimal disruption follows: Chapter 1: All Chapter 2: Section 6 Chapter 3: Sections 1520 Chapter 4: Sections 7, 1013 Chapter 5: Sections 3, 2327 Chapter 6: Sections 57, 11, 13, 1623 Chapter 7: Sections 914, 2124 Chapter 8: Sections 10, 1419 11. PREFACE xiFIGURE P-3 Letters denotecategories of problems,and asterisks indicate thatcorresponding solutionsare provided at the end ofthe text. Chapter 9: Sections 5, 9, 1520 Chapter 10: All Chapter 11: Sections 7, 1417 Chapter 12: Sections 1721 Chapter 13: AllPROBLEM SETS This edition includes six categories of problems: basic(B), challenging (C), troubleshooting (T), new (N), design (D), and HDL (H).Undesignated problems are considered to be of intermediate difficulty, be-tweenbasic and challenging. Problems for which solutions are printed in theback of the text or on the enclosed CD-ROM are marked with an asterisk (seeFigure P-3).PROJECT MANAGEMENT AND SYSTEM-LEVEL DESIGN Several real-worldexamples are included in Chapter 10 to describe the techniques usedto manage projects. These applications are generally familiar to most stu-dentsstudying electronics, and the primary example of a digital clock is fa-miliarto everyone. Many texts talk about top-down design, but this textdemonstrates the key features of this approach and how to use the moderntools to accomplish it.DATA SHEETS The CD-ROM containing Texas Instruments data sheetsthat accompanied the ninth edition has been removed.The information thatwas included on this CD-ROM is now readily available online.SIMULATION FILES This edition also includes simulation files that can beloaded into Electronics Workbench Multisim. The circuit schematics ofmany of the figures throughout the text have been captured as input files forthis popular simulation tool. Each file has some way of demonstrating the oper-ationof the circuit or reinforcing a concept. In many cases, instruments are at-tachedto the circuit and input sequences are applied to demonstrate theconcept presented in one of the figures of the text.These circuits can then bemodified as desired to expand on topics or create assignments and tutorials 12. xii PREFACEfor students. All figures in the text that have a corresponding simulation fileon the CD-ROM are identified by the icon shown in Figure P-4.IC TECHNOLOGY This new edition continues the practice begun with thelast three editions of giving more prominence to CMOS as the principal ICtechnology in small- and medium-scale integration applications. This depthof coverage has been accomplished while retaining the substantial coverageof TTL logic.Specific ChangesThe major changes in the topical coverage are listed here. Chapter 1. Many explanations covering digital/analog issues have beenupdated and improved. Chapter 2. The octal number system has been removed and the Graycode has been added. A complete standard ASCII code table has been in-cluded,along with new examples that relate ASCII characters, hex rep-resentation,and computer object code transfer files. New material onframing ASCII characters for asynchronous data transfer has also beenadded. Chapter 3. Along with some new practical examples of logic functions,the major improvement in Chapter 3 is a new analysis technique usingtables that evaluate intermediate points in the logic circuit. Chapter 4.Very few changes were necessary in Chapter 4. Chapter 5.A new section covers digital pulses and associated definitionssuch as pulse width, period, rise time, and fall time. The terminologyused for latch circuit inputs has been changed from Clear to Reset inorder to be compatible with Altera component descriptions.The definitionof a master/slave flip-flop has been removed as well. The discussion ofSchmitt trigger applications has been improved to emphasize their rolein eliminating the effects of noise. The inner workings of the 555 timerare now explained, and some improved timing circuits are proposed thatmake the device more versatile. The HDL coverage of SR and D latcheshas been rewritten to use a more intuitive behavioral description, andthe coverage of counters has been modified to focus on structural tech-niquesto interconnect flip-flop blocks. Chapter 6. Signed numbers are covered in more detail in this edition,particularly regarding sign extension in 2s complement numbers andarithmetic overflow. A new calculator hint simplifies negation of binarynumbers represented in hex. A number circle model is used to compareFIGURE P-4 The icondenotes a correspondingsimulation file on theCD-ROM. 13. PREFACE xiiisigned and unsigned number formats and help students to visualizeadd/subtract operation using both. Chapter 7. This chapter has been heavily revised to emphasize synchro-nouscounter circuits. Simple ripple counters are still introduced to pro-videa basic understanding of the concept of counting and asynchronouscascading. After examining the limitations of ripple counters in Section 2,synchronous counters are introduced in Section 3 and used in all subse-quentexamples throughout the text. The IC counters presented are the74160, 161, 162, and 163.These common devices offer an excellent assort-mentof features that teach the difference between synchronous and asyn-chronouscontrol inputs and cascading techniques.The 74190 and 191 areused as an example of a synchronous up/down counter IC, further rein-forcingthe techniques required for synchronous cascading. A new sectionis devoted to analysis techniques for synchronous circuits using JK and Dflip-flops. Synchronous design techniques now also include the use of Dflip-flop registers that best represent the way sequential circuits are im-plementedin modern PLD technology. The HDL sections have been im-provedto demonstrate the implementation of synchronous/asynchronousloading, clearing, and cascading. A new emphasis is placed on simulationand testing of HDL modules. State machines are now presented as a topic,the traditional Mealy and Moore models are defined, and a new trafficlight control system is presented as an example. Minor improvements havebeen made in the second half of Chapter 7 also. All of the problems at theend of Chapter 7 have been rewritten to reinforce the concepts. Chapter 8.This chapter remains a very technical description of the tech-nologyavailable in standard logic families and digital components. Themixed-voltage interfacing sections have been improved to cover low-voltagetechnology. The latest Texas Instruments life-cycle curve showsthe history and current position of various logic series between intro-ductionand obsolescence. Low-voltage differential signaling (LVDS) isintroduced as well. Chapter 9. The many different building blocks of digital systems are stillcovered in this chapter and demonstrated using HDL. Many other HDLtechniques, such as tristate outputs and various HDL control structures,are also introduced. A 74ALS148 is described as another example of anencoder.The examples of systems that use counters have all been updatedto synchronous operation.The serial transmission system using MUX andDEMUX is particularly improved. The technique of using a MUX toimplement SOP expressions has been explained in a more structured wayas an independent study exercise in the end-of-the-chapter problems. Chapter 10. Chapter 10, which was new to the ninth edition, has re-mainedessentially unchanged. Chapter 11.The material on bipolar DACs has been improved, and an ex-ampleof using DACs as a digital amplitude control for analog waveformsis presented. The more common A/D converter accuracy specification inthe form of / LSB is explained in this edition. Chapter 12. Minor improvements were made to this chapter to consolidateand compress some of the material on older technologies of memory suchas UV EPROM. Flash technology is still introduced using a first-generationexample, but the more recent improvements, as well as some of the appli-cationsof flash technology in modern consumer devices, are described. Chapter 13. This chapter, which was new to the ninth edition, has beenupdated to introduce the new Cyclone family of PLDs. 14. xiv PREFACERetained FeaturesThis edition retains all of the features that made the previous editions sowidely accepted. It utilizes a block diagram approach to teach the basic logicoperations without confusing the reader with the details of internal operation.All but the most basic electrical characteristics of the logic ICs are withhelduntil the reader has a firm understanding of logic principles. In Chapter 8, thereader is introduced to the internal IC circuitry. At that point, the reader caninterpret a logic blocks input and output characteristics and fit it properlyinto a complete system.The treatment of each new topic or device typically follows these steps:the principle of operation is introduced; thoroughly explained examples andapplications are presented, often using actual ICs; short review questions areposed at the end of the section; and finally, in-depth problems are availableat the end of the chapter. These problems, ranging from simple to complex,provide instructors with a wide choice of student assignments. These prob-lemsare often intended to reinforce the material without simply repeatingthe principles. They require students to demonstrate comprehension of theprinciples by applying them to different situations.This approach also helpsstudents to develop confidence and expand their knowledge of the material.The material on PLDs and HDLs is distributed throughout the text, withexamples that emphasize key features in each application. These topics ap-pearat the end of each chapter, making it easy to relate each topic to the gen-eraldiscussion earlier in the chapter or to address the general discussionseparately from the PLD/HDL coverage.The extensive troubleshooting coverage is spread over Chapters 4 through12 and includes presentation of troubleshooting principles and techniques,case studies, 25 troubleshooting examples, and 60 real troubleshooting prob-lems.When supplemented with hands-on lab exercises, this material can helpfoster the development of good troubleshooting skills.The tenth edition offers more than 200 worked-out examples, more than400 review questions, and more than 450 chapter problems/exercises. Someof these problems are applications that show how the logic devices presentedin the chapter are used in a typical microcomputer system. Answers to amajority of the problems immediately follow the Glossary.The Glossary pro-videsconcise definitions of all terms in the text that have been highlightedin boldface type.An IC index is provided at the back of the book to help readers locate eas-ilymaterial on any IC cited or used in the text. The back endsheets providetables of the most often used Boolean algebra theorems, logic gate summaries,and flip-flop truth tables for quick reference when doing problems or work-ingin the lab.SupplementsAn extensive complement of teaching and learning tools has been developedto accompany this textbook. Each component provides a unique function,and each can be used independently or in conjunction with the others.CD-ROM A CD-ROM is packaged with each copy of the text. It contains thefollowing material: MAXPLUS II Educational Version software from Altera.This is a fullyfunctional, professional-quality, integrated development environment for 15. PREFACE xvdigital systems that has been used for many years and is still supportedby Altera. Students can use it to write, compile, and simulate their de-signsat home before going to the lab.They can use the same software toprogram and test an Altera CPLD. Quartus II Web Version software from Altera. This is the latest develop-mentsystem software from Altera, which offers more advanced featuresand supports new PLD devices such as the Cyclone family of FPGAs,found on many of the newest educational boards. Tutorials. Gregory Moss has developed tutorials that have been usedsuccessfully for several years to teach introductory students how to useAltera MAXPLUS II software. These tutorials are available in PDFand PPT (Microsoft PowerPoint presentation) formats and have beenadapted to teach Quartus II as well.With the help of these tutorials, any-onecan learn to modify and test all the examples presented in this text,as well as develop his or her own designs. Design files from the textbook figures. More than 40 design files in eachlanguage are presented in figures throughout the text. Students can loadthese into the Altera software and test them. Solutions to selected problems: HDL design files. A few of the end-of-chapterproblem solutions are available to students. (All of the HDLsolutions are available to instructors in the Instructors Resource Manual.)Solutions for Chapter 7 problems include some large graphic and HDLfiles that are not published in the back of the book but are available onthe enclosed CD-ROM. Circuits from the text rendered in Multisim. Students can open andwork interactively with approximately 100 circuits to increase their un-derstandingof concepts and prepare for laboratory activities. TheMultisim circuit files are provided for use by anyone who has Multisimsoftware. Anyone who does not have Multisim software and wishes topurchase it in order to use the circuit files may do so by ordering it fromwww.prenhall.com/ewb. Supplemental material introducing microprocessors and microcon-trollers.For the flexibility to serve the diverse needs of the many differ-entschools, an introduction to this topic is presented as a convenientbridge between a digital systems course and an introduction to micro-processors/microcontrollers course.STUDENT RESOURCES Lab Manual: A Design Approach. This lab manual, written by GregoryMoss, contains topical units with lab projects that emphasize simulationand design. It utilizes the Altera MAXPLUS II or Quartus II software inits programmable logic exercises and features both schematic captureand hardware description language techniques. The new edition con-tainsmany new projects and examples. (ISBN 0-13-188138-8) Lab Manual: A Troubleshooting Approach. This manual, written by JimDeLoach and Frank Ambrosio, is presented with an analysis and trou-bleshootingapproach and is fully updated for this edition of the text.(ISBN 0-13-188136-1) Companion Website (www.prenhall.com/tocci). This site offers students afree online study guide with which they can review the material learnedin the text and check their understanding of key topics. 16. INSTRUCTOR RESOURCES Instructors Resource Manual. This manual contains worked-out solutionsfor all end-of-chapter problems in this textbook. (ISBN 0-13-172665-X) Lab Solutions Manual. Worked-out lab results for both lab manuals arefeatured in this manual. (ISBN 0-13-172664-1) PowerPoint presentations. Figures from the text, in addition to LectureNotes for each chapter, are available on CD-ROM. (ISBN 0-13-172667-6) TestGen. A computerized test bank is available on CD-ROM. (ISBN 0-13-172666-8)To access supplementary materials online, instructors need to request aninstructor access code. Go to www.prenhall.com, click the Instructor ResourceCenter link, and then click Register Today for an instructor access code.Within48 hours after registering, you will receive a confirming e-mail including aninstructor access code.When you have received your code, go to the site andlog on for full instructions on downloading the materials you wish to use.ACKNOWLEDGMENTSWe are grateful to all those who evaluated the ninth edition and providedanswers to an extensive questionnaire: Ali Khabari,Wentworth Institute ofTechnology; Al Knebel, Monroe Community College; Rex Fisher, BrighamYoung University; Alan Niemi, LeTourneau University; and Roger Sash, Uni-versityof Nebraska. Their comments, critiques, and suggestions were givenserious consideration and were invaluable in determining the final form ofthe tenth edition.We also are greatly indebted to Professor Frank Ambrosio, Monroe Com-munityCollege, for his usual high-quality work on the indexes and the Ins-tructorsResource Manual; and Professor Thomas L. Robertson, PurdueUniversity, for providing his magnetic levitation system as an example; andProfessors Russ Aubrey and Gene Harding, Purdue University, for their tech-nicalreview of topics and many suggestions for improvements.We appreci-atethe cooperation of Mike Phipps and the Altera Corporation for theirsupport in granting permission to use their software package and their fig-uresfrom technical publications.A writing project of this magnitude requires conscientious and profes-sionaleditorial support, and Prentice Hall came through again in typicalfashion. We thank the staffs at Prentice Hall and TechBooks/GTS for theirhelp to make this publication a success.And finally, we want to let our wives and our children know how much weappreciate their support and their understanding.We hope that we can even-tuallymake up for all the hours we spent away from them while we workedon this revision.Ronald J.TocciNeal S.WidmerGregory L. Mossxvi PREFACE 17. xviiBRIEF CONTENTSCHAPTER 1 Introductory Concepts 2CHAPTER 2 Number Systems and Codes 24CHAPTER 3 Describing Logic Circuits 54CHAPTER 4 Combinational Logic Circuits 118CHAPTER 5 Flip-Flops and Related Devices 208CHAPTER 6 Digital Arithmetic: Operations and Circuits 296CHAPTER 7 Counters and Registers 360CHAPTER 8 Integrated-Circuit Logic Families 488CHAPTER 9 MSI Logic Circuits 576CHAPTER 10 Digital System Projects Using HDL 676CHAPTER 11 Interfacing with the Analog World 718CHAPTER 12 Memory Devices 786CHAPTER 13 Programmable Logic Device Architectures 868Glossary 898Answers to Selected Problems 911Index of ICs 919Index 922 18. xixCONTENTSCHAPTER 1 Introductory Concepts 21-1 Numerical Representations 41-2 Digital and Analog Systems 51-3 Digital Number Systems 101-4 Representing Binary Quantities 131-5 Digital Circuits/Logic Circuits 151-6 Parallel and Serial Transmission 171-7 Memory 181-8 Digital Computers 19CHAPTER 2 Number Systems and Codes 242-1 Binary-to-Decimal Conversions 262-2 Decimal-to-Binary Conversions 262-3 Hexadecimal Number System 292-4 BCD Code 332-5 The Gray Code 352-6 Putting It All Together 372-7 The Byte, Nibble, and Word 372-8 Alphanumeric Codes 392-9 Parity Method for Error Detection 412-10 Applications 44 19. xx CONTENTSChapter 3 Describing Logic Circuits 543-1 Boolean Constants and Variables 573-2 Truth Tables 573-3 OR Operation with OR Gates 583-4 AND Operation with AND Gates 623-5 NOT Operation 653-6 Describing Logic Circuits Algebraically 663-7 Evaluating Logic-Circuit Outputs 683-8 Implementing Circuits from BooleanExpressions 713-9 NOR Gates and NAND Gates 733-10 Boolean Theorems 763-11 DeMorgans Theorems 803-12 Universality of NAND Gates and NOR Gates 833-13 Alternate Logic-Gate Representations 863-14 Which Gate Representation to Use 893-15 IEEE/ANSI Standard Logic Symbols 953-16 Summary of Methods to Describe Logic Circuits 963-17 Description Languages Versus ProgrammingLanguages 983-18 Implementing Logic Circuits with PLDs 1003-19 HDL Format and Syntax 1023-20 Intermediate Signals 105Chapter 4 Combinational Logic Circuits 1184-1 Sum-of-Products Form 1204-2 Simplifying Logic Circuits 1214-3 Algebraic Simplification 1214-4 Designing Combinational Logic Circuits 1274-5 Karnaugh Map Method 1334-6 Exclusive-OR and Exclusive-NOR Circuits 1444-7 Parity Generator and Checker 1494-8 Enable/Disable Circuits 1514-9 Basic Characteristics of Digital ICs 1534-10 Troubleshooting Digital Systems 1604-11 Internal Digital IC Faults 1624-12 External Faults 1664-13 Troubleshooting Case Study 1684-14 Programmable Logic Devices 1704-15 Representing Data in HDL 1774-16 Truth Tables Using HDL 1814-17 Decision Control Structures in HDL 184 20. CONTENTS xxiChapter 5 Flip-Flops and Related Devices 2085-1 NAND Gate Latch 2115-2 NOR Gate Latch 2165-3 Troubleshooting Case Study 2195-4 Digital Pulses 2205-5 Clock Signals and Clocked Flip-Flops 2215-6 Clocked S-R Flip-Flop 2245-7 Clocked J-K Flip-Flop 2275-8 Clocked D Flip-Flop 2305-9 D Latch (Transparent Latch) 2325-10 Asynchronous Inputs 2335-11 IEEE/ANSI Symbols 2365-12 Flip-Flop Timing Considerations 2385-13 Potential Timing Problem in FF Circuits 2415-14 Flip-Flop Applications 2435-15 Flip-Flop Synchronization 2435-16 Detecting an Input Sequence 2445-17 Data Storage and Transfer 2455-18 Serial Data Transfer: Shift Registers 2475-19 Frequency Division and Counting 2505-20 Microcomputer Application 2545-21 Schmitt-Trigger Devices 2565-22 One-Shot (Monostable Multivibrator) 2565-23 Clock Generator Circuits 2605-24 Troubleshooting Flip-Flop Circuits 2645-25 Sequential Circuits Using HDL 2685-26 Edge-Triggered Devices 2725-27 HDL Circuits with Multiple Components 277Chapter 6 Digital Arithmetic:Operations and Circuits 2966-1 Binary Addition 2986-2 Representing Signed Numbers 2996-3 Addition in the 2s-Complement System 3066-4 Subtraction in the 2s-Complement System 3076-5 Multiplication of Binary Numbers 3106-6 Binary Division 3116-7 BCD Addition 3126-8 Hexadecimal Arithmetic 3146-9 Arithmetic Circuits 3176-10 Parallel Binary Adder 3186-11 Design of a Full Adder 320 21. xxii CONTENTS6-12 Complete Parallel Adder with Registers 3236-13 Carry Propagation 3256-14 Integrated-Circuit Parallel Adder 3266-15 2s-Complement System 3286-16 ALU Integrated Circuits 3316-17 Troubleshooting Case Study 3356-18 Using TTL Library Functions with HDL 3376-19 Logical Operations on Bit Arrays 3386-20 HDL Adders 3406-21 Expanding the Bit Capacity of a Circuit 343Chapter 7 Counters and Registers 3607-1 Asynchronous (Ripple) Counters 3627-2 Propagation Delay in Ripple Counters 3657-3 Synchronous (Parallel) Counters 3677-4 Counters with MOD Numbers 2N 3707-5 Synchronous Down and Up/Down Counters 3777-6 Presettable Counters 3797-7 IC Synchronous Counters 3807-8 Decoding a Counter 3897-9 Analyzing Synchronous Counters 3937-10 Synchronous Counter Design 3967-11 Basic Counters Using HDLs 4057-12 Full-Featured Counters in HDL 4127-13 Wiring HDL Modules Together 4177-14 State Machines 4257-15 Integrated-Circuit Registers 4377-16 Parallel In/Parallel OutThe 74ALS174/74HC174 4377-17 Serial In/Serial OutThe 74ALS166/74HC166 4397-18 Parallel In/Serial OutThe 74ALS165/74HC165 4417-19 Serial In/Parallel OutThe 74ALS164/74HC164 4437-20 Shift-Register Counters 4457-21 Troubleshooting 4507-22 HDL Registers 4527-23 HDL Ring Counters 4597-24 HDL One-Shots 461Chapter 8 Integrated-Circuit Logic Families 4888-1 Digital IC Terminology 4908-2 The TTL Logic Family 4988-3 TTL Data Sheets 5028-4 TTL Series Characteristics 506 22. CONTENTS xxiii8-5 TTL Loading and Fan-Out 5098-6 Other TTL Characteristics 5148-7 MOS Technology 5188-8 Complementary MOS Logic 5218-9 CMOS Series Characteristics 5238-10 Low-Voltage Technology 5308-11 Open-Collector/Open-Drain Outputs 5338-12 Tristate (Three-State) Logic Outputs 5388-13 High-Speed Bus Interface Logic 5418-14 The ECL Digital IC Family 5438-15 CMOS Transmission Gate (Bilateral Switch) 5468-16 IC Interfacing 5488-17 Mixed-Voltage Interfacing 5538-18 Analog Voltage Comparators 5548-19 Troubleshooting 556Chapter 9 MSI Logic Circuits 5769-1 Decoders 5779-2 BCD-to-7-Segment Decoder/Drivers 5849-3 Liquid-Crystal Displays 5879-4 Encoders 5919-5 Troubleshooting 5979-6 Multiplexers (Data Selectors) 5999-7 Multiplexer Applications 6049-8 Demultiplexers (Data Distributors) 6109-9 More Troubleshooting 6179-10 Magnitude Comparator 6219-11 Code Converters 6249-12 Data Busing 6289-13 The 74ALS173/HC173 Tristate Register 6299-14 Data Bus Operation 6329-15 Decoders Using HDL 6389-16 The HDL 7-Segment Decoder/Driver 6429-17 Encoders Using HDL 6459-18 HDL Multiplexers and Demultiplexers 6489-19 HDL Magnitude Comparators 6529-20 HDL Code Converters 653Chapter 10 Digital System Projects Using HDL 67610-1 Small-Project Management 67810-2 Stepper Motor Driver Project 67910-3 Keypad Encoder Project 687 23. xxiv CONTENTS10-4 Digital Clock Project 69310-5 Frequency Counter Project 710Chapter 11 Interfacing with the Analog World 71811-1 Review of Digital Versus Analog 71911-2 Digital-to-Analog Conversion 72111-3 D/A-Converter Circuitry 72811-4 DAC Specifications 73311-5 An Integrated-Circuit DAC 73511-6 DAC Applications 73611-7 Troubleshooting DACs 73811-8 Analog-to-Digital Conversion 73911-9 Digital-Ramp ADC 74011-10 Data Acquisition 74511-11 Successive-Approximation ADC 74911-12 Flash ADCs 75511-13 Other A/D Conversion Methods 75711-14 Sample-and-Hold Circuits 76111-15 Multiplexing 76211-16 Digital Storage Oscilloscope 76411-17 Digital Signal Processing (DSP) 765Chapter 12 Memory Devices 78412-1 Memory Terminology 78612-2 General Memory Operation 79012-3 CPUMemory Connections 79312-4 Read-Only Memories 79512-5 ROM Architecture 79612-6 ROM Timing 79912-7 Types of ROMs 80012-8 Flash Memory 80812-9 ROM Applications 81112-10 Semiconductor RAM 81412-11 RAM Architecture 81512-12 Static RAM (SRAM) 81812-13 Dynamic RAM (DRAM) 82312-14 Dynamic RAM Structure and Operation 82412-15 DRAM Read/Write Cycles 82912-16 DRAM Refreshing 83112-17 DRAM Technology 83412-18 Expanding Word Size and Capacity 83612-19 Special Memory Functions 844 24. CONTENTS xxv12-20 Troubleshooting RAM Systems 84712-21 Testing ROM 852Chapter 13 Programmable Logic DeviceArchitectures 86813-1 Digital Systems Family Tree 87013-2 Fundamentals of PLD Circuitry 87513-3 PLD Architectures 87713-4 The GAL 16V8 (Generic Array Logic) 88113-5 The Altera EPM7128S CPLD 88513-6 The Altera FLEX10K Family 89013-7 The Altera Cyclone Family 894Glossary 898Answers to Selected Problems 911Index of ICs 919Index 922 25. Digital SystemsPrinciples and Applications 26. C H A P T E R 1INTRODUCTORYCONCEPTS OUTLINE1-1 Numerical Representations1-2 Digital and Analog Systems1-3 Digital Number Systems1-4 Representing BinaryQuantities1-5 Digital Circuits/LogicCircuits1-6 Parallel and SerialTransmission1-7 Memory1-8 Digital Computers 27. 3 OBJECTIVESUpon completion of this chapter, you will be able to: Distinguish between analog and digital representations. Cite the advantages and drawbacks of digital techniques comparedwith analog. Understand the need for analog-to-digital converters (ADCs) anddigital-to-analog converters (DACs). Recognize the basic characteristics of the binary number system. Convert a binary number to its decimal equivalent. Count in the binary number system. Identify typical digital signals. Identify a timing diagram. State the differences between parallel and serial transmission. Describe the property of memory. Describe the major parts of a digital computer and understand theirfunctions. Distinguish among microcomputers, microprocessors, andmicrocontrollers. INTRODUCTIONIn todays world, the term digital has become part of our everyday vocabu-larybecause of the dramatic way that digital circuits and digital techniqueshave become so widely used in almost all areas of life: computers, automa-tion,robots, medical science and technology, transportation, telecommuni-cations,entertainment, space exploration, and on and on.You are about tobegin an exciting educational journey in which you will discover the funda-mentalprinciples, concepts, and operations that are common to all digitalsystems, from the simplest on/off switch to the most complex computer. Ifthis book is successful, you should gain a deep understanding of how alldigital systems work, and you should be able to apply this understanding tothe analysis and troubleshooting of any digital system.We start by introducing some underlying concepts that are a vital partof digital technology; these concepts will be expanded on as they areneeded later in the book.We also introduce some of the terminology that isnecessary when embarking on a new field of study, and add to this list ofimportant terms in every chapter. 28. 4 CHAPTER 1/INTRODUCTORY CONCEPTS1-1 NUMERICAL REPRESENTATIONSIn science, technology, business, and, in fact, most other fields of endeavor,we are constantly dealing with quantities. Quantities are measured, moni-tored,recorded, manipulated arithmetically, observed, or in some other wayutilized in most physical systems. It is important when dealing with variousquantities that we be able to represent their values efficiently and accu-rately.There are basically two ways of representing the numerical value ofquantities: analog and digital.Analog RepresentationsIn analog representation a quantity is represented by a continuously vari-able,proportional indicator. An example is an automobile speedometer fromthe classic muscle cars of the 1960s and 1970s. The deflection of the needleis proportional to the speed of the car and follows any changes that occur asthe vehicle speeds up or slows down. On older cars, a flexible mechanicalshaft connected the transmission to the speedometer on the dash board. It isinteresting to note that on newer cars, the analog representation is usuallypreferred even though speed is now measured digitally.Thermometers before the digital revolution used analog representation tomeasure temperature, and many are still in use today. Mercury thermometersuse a column of mercury whose height is proportional to temperature. Thesedevices are being phased out of the market because of environmental con-cerns,but nonetheless they are an excellent example of analog representa-tion.Another example is an outdoor thermometer on which the position of thepointer rotates around a dial as a metal coil expands and contracts with tem-peraturechanges. The position of the pointer is proportional to the tempera-ture.Regardless of how small the change in temperature, there will be aproportional change in the indication.In these two examples the physical quantities (speed and temperature) arebeing coupled to an indicator by purely mechanical means. In electrical analogsystems, the physical quantity that is being measured or processed is convertedto a proportional voltage or current (electrical signal). This voltage or currentis then used by the system for display, processing, or control purposes.Sound is an example of a physical quantity that can be represented by anelectrical analog signal. A microphone is a device that generates an outputvoltage that is proportional to the amplitude of the sound waves that strikeit.Variations in the sound waves will produce variations in the microphonesoutput voltage.Tape recordings can then store sound waves by using the out-putvoltage of the microphone to proportionally change the magnetic field onthe tape.Analog quantities such as those cited above have an important charac-teristic,no matter how they are represented: they can vary over a continuousrange of values. The automobile speed can have any value between zero and,say, 100 mph. Similarly, the microphone output might have any value withina range of zero to 10 mV (e.g., 1 mV, 2.3724 mV, 9.9999 mV).Digital RepresentationsIn digital representation the quantities are represented not by continuouslyvariable indicators but by symbols called digits. As an example, consider thedigital clock, which provides the time of day in the form of decimal digits thatrepresent hours and minutes (and sometimes seconds). As we know, the timeof day changes continuously, but the digital clock reading does not changecontinuously; rather, it changes in steps of one per minute (or per second). In 29. SECTION 1-2/DIGITAL AND ANALOG SYSTEMS 5other words, this digital representation of the time of day changes in discretesteps, as compared with the representation of time provided by an analog acline-powered wall clock, where the dial reading changes continuously.The major difference between analog and digital quantities, then, can besimply stated as follows:Kanalog continuousdigital discrete (step by step)KBecause of the discrete nature of digital representations, there is no ambiguitywhen reading the value of a digital quantity, whereas the value of an analogquantity is often open to interpretation. In practice, when we take a measure-mentof an analog quantity, we always round to a convenient level of preci-sion.In other words, we digitize the quantity.The digital representation is theresult of assigning a number of limited precision to a continuously variablequantity. For example, when you take your temperature with a mercury (ana-log)thermometer, the mercury column is usually between two graduation lines,but you would pick the nearest line and assign it a number of, say, 98.6F.EXAMPLE 1-1 Which of the following involve analog quantities and which involve digitalquantities?(a) Ten-position switch(b) Current flowing from an electrical outlet(c) Temperature of a room(d) Sand grains on the beach(e) Automobile fuel gaugeSolution(a) Digital(b) Analog(c) Analog(d) Digital, since the number of grains can be only certain discrete (integer)values and not every possible value over a continuous range(e) Analog, if needle type; digital, if numerical readout or bar graph displayREVIEW QUESTION * 1. Concisely describe the major difference between analog and digitalquantities.1-2 DIGITAL AND ANALOG SYSTEMSA digital system is a combination of devices designed to manipulate logicalinformation or physical quantities that are represented in digital form; thatis, the quantities can take on only discrete values. These devices are most*Answers to review questions are found at the end of the chapter in which they occur. 30. 6 CHAPTER 1/INTRODUCTORY CONCEPTSoften electronic, but they can also be mechanical, magnetic, or pneumatic.Some of the more familiar digital systems include digital computers and cal-culators,digital audio and video equipment, and the telephone systemtheworlds largest digital system.An analog system contains devices that manipulate physical quantitiesthat are represented in analog form. In an analog system, the quantities canvary over a continuous range of values. For example, the amplitude of theoutput signal to the speaker in a radio receiver can have any value betweenzero and its maximum limit. Other common analog systems are audio ampli-fiers,magnetic tape recording and playback equipment, and a simple lightdimmer switch.Advantages of Digital TechniquesAn increasing majority of applications in electronics, as well as in most othertechnologies, use digital techniques to perform operations that were onceperformed using analog methods. The chief reasons for the shift to digitaltechnology are:1. Digital systems are generally easier to design. The circuits used in digitalsystems are switching circuits, where exact values of voltage or currentare not important, only the range (HIGH or LOW) in which they fall.2. Information storage is easy. This is accomplished by special devices andcircuits that can latch onto digital information and hold it for as long asnecessary, and mass storage techniques that can store billions of bits ofinformation in a relatively small physical space. Analog storage capabil-itiesare, by contrast, extremely limited.3. Accuracy and precision are easier to maintain throughout the system. Oncea signal is digitized, the information it contains does not deteriorate as itis processed. In analog systems, the voltage and current signals tend tobe distorted by the effects of temperature, humidity, and component tol-erancevariations in the circuits that process the signal.4. Operation can be programmed. It is fairly easy to design digital systemswhose operation is controlled by a set of stored instructions called aprogram. Analog systems can also be programmed, but the variety andthe complexity of the available operations are severely limited.5. Digital circuits are less affected by noise. Spurious fluctuations in voltage(noise) are not as critical in digital systems because the exact value of avoltage is not important, as long as the noise is not large enough to pre-ventus from distinguishing a HIGH from a LOW.6. More digital circuitry can be fabricated on IC chips. It is true that analogcircuitry has also benefited from the tremendous development of ICtechnology, but its relative complexity and its use of devices that cannotbe economically integrated (high-value capacitors, precision resistors,inductors, transformers) have prevented analog systems from achievingthe same high degree of integration.Limitations of Digital TechniquesThere are really very few drawbacks when using digital techniques. The twobiggest problems are:The real world is analog.Processing digitized signals takes time. 31. SECTION 1-2/DIGITAL AND ANALOG SYSTEMS 7Most physical quantities are analog in nature, and these quantities are oftenthe inputs and outputs that are being monitored, operated on, and controlledby a system. Some examples are temperature, pressure, position, velocity, liq-uidlevel, flow rate, and so on.We are in the habit of expressing these quan-titiesdigitally, such as when we say that the temperature is ( whenwe want to be more precise), but we are really making a digital approxima-tionto an inherently analog quantity.To take advantage of digital techniques when dealing with analog inputsand outputs, four steps must be followed:1. Convert the physical variable to an electrical signal (analog).2. Convert the electrical (analog) signal into digital form.3. Process (operate on) the digital information.4. Convert the digital outputs back to real-world analog form.An entire book could be written about step 1 alone.There are many kindsof devices that convert various physical variables into electrical analog sig-nals(sensors).These are used to measure things that are found in our realanalog world. On your car alone, there are sensors for fluid level (gas tank),temperature (climate control and engine), velocity (speedometer), accelera-tion(airbag collision detection), pressure (oil, manifold), and flow rate (fuel),to name just a few.To illustrate a typical system that uses this approach Figure 1-1 describesa precision temperature regulation system. A user pushes up or down buttonsto set the desired temperature in 0.1increments (digital representation). Atemperature sensor in the heated space converts the measured temperatureto a proportional voltage. This analog voltage is converted to a digital quan-tityby an analog-to-digital converter (ADC). This value is then compared tothe desired value and used to determine a digital value of how much heat isneeded. The digital value is converted to an analog quantity (voltage) by adigital-to-analog converter (DAC). This voltage is applied to a heating ele-ment,which will produce heat that is related to the voltage applied and willaffect the temperature of the space.64 63.8FIGURE 1-1 Block diagram of a precision digital temperature control system.Temperature controlledspaceDigital input:Set Desired TemperatureDigital ProcessorDigitalAnalogconversionAnalogDigitalconversionHeatSensorAnalog signal representingactual temperatureDigital signal representingactual temperatureDigital signal representingpower (voltage) to heater+Another good example where conversion between analog and digitaltakes place is in the recording of audio. Compact disks (CDs) have replacedcassette tapes because they provide a much better means for recording and 32. 8 CHAPTER 1/INTRODUCTORY CONCEPTSplaying back music. The process works something like this: (1) sounds frominstruments and human voices produce an analog voltage signal in a micro-phone;(2) this analog signal is converted to a digital format using an analog-to-digital conversion process; (3) the digital information is stored on the CDssurface; (4) during playback, the CD player takes the digital informationfrom the CD surface and converts it into an analog signal that is then ampli-fiedand fed to a speaker, where it can be picked up by the human ear.The second drawback to digital systems is that processing these digitizedsignals (lists of numbers) takes time. And we also need to convert betweenthe analog and digital forms of information, which can add complexity andexpense to a system.The more precise the numbers need to be, the longer ittakes to process them. In many applications, these factors are outweighed bythe numerous advantages of using digital techniques, and so the conversionbetween analog and digital quantities has become quite commonplace in thecurrent technology.There are situations, however, where use of analog techniques is simpleror more economical. For example, several years ago, a colleague (TomRobertson) decided to create a control system demonstration for tourgroups. He planned to suspend a metallic object in a magnetic field, as shownin Figure 1-2. An electromagnet was made by winding a coil of wire and con-trollingthe amount of current through the coil.The position of the metal ob-jectwas measured by passing an infrared light beam across the magneticfield. As the object drew closer to the magnetic coil, it began to block thelight beam. By measuring small changes in the light level, the magnetic fieldcould be controlled to keep the metal object hovering and stationary, with nostrings attached. All attempts at using a microcomputer to measure thesevery small changes, run the control calculations, and drive the magnetproved to be too slow, even when using the fastest, most powerful PC avail-ableat the time. His final solution used just a couple of op-amps and a fewdollars worth of other components: a totally analog approach.Today we haveaccess to processors fast enough and measurement techniques preciseenough to accomplish this feat, but the simplest solution is still analog.(a) (b)FIGURE 1-2 A magnetic levitation system suspending: (a) a globe with a steelplate inserted and (b) a hammer.It is common to see both digital and analog techniques employed withinthe same system to be able to profit from the advantages of each. In thesehybrid systems, one of the most important parts of the design phase involves 33. SECTION 1-2/DIGITAL AND ANALOG SYSTEMS 9determining what parts of the system are to be analog and what parts are tobe digital. The trend in most systems is to digitize the signal as early as pos-sibleand convert it back to analog as late as possible as the signals flowthrough the system.The Future Is DigitalThe advances in digital technology over the past three decades have beennothing short of phenomenal, and there is every reason to believe that moreis coming.Think of the everyday items that have changed from analog formatto digital in your lifetime. An indoor/outdoor wireless digital thermometercan be purchased for less then $10.00. Cars have gone from having very fewelectronic controls to being predominantly digitally controlled vehicles.Digital audio has moved us to the compact disk and MP3 player. Digitalvideo brought the DVD. Digital home video and still cameras; digital record-ingwith systems like TiVo; digital cellular phones; and digital imaging in x-ray,magnetic resonance imaging (MRI), and ultrasound systems in hospitalsare just a few of the applications that have been taken over by the digitalrevolution. As soon as the infrastructure is in place, telephone and televisionsystems will go digital. The growth rate in the digital realm continues to bestaggering. Maybe your automobile is equipped with a system such as GMsOn Star, which turns your dashboard into a hub for wireless communication,information, and navigation. You may already be using voice commands tosend or retrieve e-mail, call for a traffic report, check on the cars mainte-nanceneeds, or just switch radio stations or CDsall without taking yourhands off the wheel or your eyes off the road. Cars can report their exact lo-cationin case of emergency or mechanical breakdown. In the coming yearswireless communication will continue to expand coverage to provide con-nectivitywherever you are. Telephones will be able to receive, sort, andmaybe respond to incoming calls like a well-trained secretary.The digital tel-evisionrevolution will provide not only higher definition of the picture, butalso much more flexibility in programming.You will be able to select the pro-gramsthat you want to view and load them into your televisions memory, al-lowingyou to pause or replay scenes at your convenience, very much likeviewing a DVD today. As virtual reality continues to improve, you will beable to interact with the subject matter you are studying.This may not soundexciting when studying electronics, but imagine studying history from thestandpoint of being a participant, or learning proper techniques for every-thingfrom athletics to surgery through simulations based on your actualperformance.Digital technology will continue its high-speed incursion into current ar-easof our lives as well as break new ground in ways we may never have con-sidered.These applications (and many more) are based on the principlespresented in this text.The software tools to develop complex systems are con-stantlybeing upgraded and are available to anyone over the Web. We willstudy the technical underpinnings necessary to communicate with any ofthese tools, and prepare you for a fascinating and rewarding career.REVIEW QUESTIONS 1. What are the advantages of digital techniques over analog?2. What is the chief limitation to the use of digital techniques? 34. 1-3 DIGITAL NUMBER SYSTEMSMany number systems are in use in digital technology.The most common arethe decimal, binary, octal, and hexadecimal systems. The decimal system isclearly the most familiar to us because it is a tool that we use every day.Examining some of its characteristics will help us to understand the othersystems better.Decimal SystemThe decimal system is composed of 10 numerals or symbols.These 10 symbolsare 0, 1, 2, 3, 4, 5, 6, 7, 8, 9; using these symbols as digits of a number,we can ex-pressany quantity.The decimal system, also called the base-10 system becauseit has 10 digits, has evolved naturally as a result of the fact that people have 10fingers. In fact, the word digit is derived from the Latin word for finger.The decimal system is a positional-value system in which the value of adigit depends on its position. For example, consider the decimal number 453.We know that the digit 4 actually represents 4 hundreds, the 5 represents 5tens, and the 3 represents 3 units. In essence, the 4 carries the most weight ofthe three digits; it is referred to as the most significant digit (MSD).The 3 car-riesthe least weight and is called the least significant digit (LSD).Consider another example, 27.35.This number is actually equal to 2 tensplus 7 units plus 3 tenths plus 5 hundredths, or 2107130.1 50.01. The decimal point is used to separate the integer and fractionalparts of the number.More rigorously, the various positions relative to the decimal point carryweights that can be expressed as powers of 10.This is illustrated in Figure 1-3,where the number 2745.214 is represented. The decimal point separates thepositive powers of 10 from the negative powers.The number 2745.214 is thusequal to(2 * 10+3) + (7 * 10+2) + (4 * 101) + (5 * 100)+ (2 * 10-1) + (1 * 10-2) + (4 * 10-3)10 CHAPTER 1/INTRODUCTORY CONCEPTSPositional values103 102101 100 101102 1032 7 4 5 . 2 1 4(weights)DecimalpointMSD LSDFIGURE 1-3 Decimalposition values as powersof 10.In general, any number is simply the sum of the products of each digit valueand its positional value.Decimal CountingWhen counting in the decimal system, we start with 0 in the units positionand take each symbol (digit) in progression until we reach 9. Then we add a1 to the next higher position and start over with 0 in the first position (see 35. SECTION 1-3/DIGITAL NUMBER SYSTEMS 11Figure 1-4). This process continues until the count of 99 is reached. Then weadd a 1 to the third position and start over with 0s in the first two positions.The same pattern is followed continuously as high as we wish to count.It is important to note that in decimal counting, the units position (LSD)changes upward with each step in the count, the tens position changes up-wardevery 10 steps in the count, the hundreds position changes upwardevery 100 steps in the count, and so on.Another characteristic of the decimal system is that using only two deci-malplaces,we can count through different numbers (0 to 99).* With102 = 100three places we can count through 1000 numbers (0 to 999), and so on. In gen-eral,with N places or digits,we can count through 10N different numbers, start-ingwith and including zero.The largest number will always be10N - 1.Binary SystemUnfortunately, the decimal number system does not lend itself to convenientimplementation in digital systems. For example, it is very difficult to designelectronic equipment so that it can work with 10 different voltage levels(each one representing one decimal character, 0 through 9). On the otherhand, it is very easy to design simple, accurate electronic circuits that oper-atewith only two voltage levels. For this reason, almost every digital systemuses the binary (base-2) number system as the basic number system of itsoperations. Other number systems are often used to interpret or representbinary quantities for the convenience of the people who work with and usethese digital systems.In the binary system there are only two symbols or possible digit values, 0and 1. Even so, this base-2 system can be used to represent any quantity thatcan be represented in decimal or other number systems. In general though, itwill take a greater number of binary digits to express a given quantity.All of the statements made earlier concerning the decimal system areequally applicable to the binary system.The binary system is also a positional-valuesystem, wherein each binary digit has its own value or weight expressedas a power of 2. This is illustrated in Figure 1-5. Here, places to the left of the*Zero is counted as a number.0123456789101112131415161718192021222324252627282930991001011021031992009991000FIGURE 1-4 Decimalcounting. 36. 12 CHAPTER 1/INTRODUCTORY CONCEPTS23 2221 20 21 22 231 0 1 1 1 0 1PositionalvaluesBinarypointMSB LSBFIGURE 1-5 Binary positionvalues as powers of 2.binary point (counterpart of the decimal point) are positive powers of 2, andplaces to the right are negative powers of 2.The number 1011.101 is shown rep-resentedin the figure. To find its equivalent in the decimal system, we simplytake the sum of the products of each digit value (0 or 1) and its positional value:1011.1012 = (1 * 23) + (0 * 22) + (1 * 21) + (1 * 20)+ (1 * 2-1) + (0 * 2-2) + (1 * 2-3)= 8 + 0 + 2 + 1 + 0.5 + 0 + 0.125= 11.62510Notice in the preceding operation that subscripts (2 and 10) were used to in-dicatethe base in which the particular number is expressed.This conventionis used to avoid confusion whenever more than one number system is beingemployed.In the binary system, the term binary digit is often abbreviated to theterm bit, which we will use from now on. Thus, in the number expressed inFigure 1-5 there are four bits to the left of the binary point, representing theinteger part of the number, and three bits to the right of the binary point, rep-resentingthe fractional part. The most significant bit (MSB) is the leftmostbit (largest weight).The least significant bit (LSB) is the rightmost bit (small-estweight).These are indicated in Figure 1-5. Here, the MSB has a weight of23; the LSB has a weight of2-3.Binary CountingWhen we deal with binary numbers, we will usually be restricted to a spe-cificnumber of bits. This restriction is based on the circuitry used to repre-sentthese binary numbers. Lets use four-bit binary numbers to illustrate themethod for counting in binary.The sequence (shown in Figure 1-6) begins with all bits at 0; this is calledthe zero count. For each successive count, the units (20) position toggles; thatis, it changes from one binary value to the other. Each time the units bitchanges from a 1 to a 0, the twos (21) position will toggle (change states). Eachtime the twos position changes from 1 to 0, the fours (22) position will toggle(change states). Likewise, each time the fours position goes from 1 to 0, theeights (23) position toggles. This same process would be continued for thehigher-order bit positions if the binary number had more than four bits.The binary counting sequence has an important characteristic, as shown inFigure 1-6. The units bit (LSB) changes either from 0 to 1 or 1 to 0 with eachcount.The second bit (twos position) stays at 0 for two counts, then at 1 for twocounts, then at 0 for two counts, and so on.The third bit (fours position) staysat 0 for four counts, then at 1 for four counts, and so on.The fourth bit (eightsposition) stays at 0 for eight counts, then at 1 for eight counts. If we wanted to 37. SECTION 1-4/REPRESENTING BINARY QUANTITIES 13Weights 23 = 8 22 = 4 21 = 2 20 = 1 Decimal equivalent01234567891011121314150000000011111111000011110000111100110011001100110101010101010101LSBFIGURE 1-6 Binarycounting sequence.count further,we would add more places, and this pattern would continue with0s and 1s alternating in groups of 2N-1.For example, using a fifth binary place,the fifth bit would alternate sixteen 0s, then sixteen 1s, and so on.As we saw for the decimal system, it is also true for the binary system thatby using N bits or places, we can go through 2N counts. For example, with twobits we can go through counts (002 through 112); with four bits we cango through counts (00002 through 11112); and so on. The last countwill always be all 1s and is equal to in the decimal system. For exam-ple,2N-124 = 1622 = 4using four bits, the last count is 11112 = 24-1 = 1510.EXAMPLE 1-2 What is the largest number that can be represented using eight bits?Solution2N-1 = 28-1 = 25510 = 111111112.This has been a brief introduction of the binary number system and itsrelation to the decimal system.We will spend much more time on these twosystems and several others in the next chapter.REVIEW QUESTIONS 1. What is the decimal equivalent of 11010112?2. What is the next binary number following 101112 in the counting sequence?3. What is the largest decimal value that can be represented using 12 bits?1-4 REPRESENTING BINARY QUANTITIESIn digital systems, the information being processed is usually present in bi-naryform. Binary quantities can be represented by any device that has onlytwo operating states or possible conditions. For example, a switch has onlytwo states: open or closed. We can arbitrarily let an open switch represent 38. 14 CHAPTER 1/INTRODUCTORY CONCEPTSbinary 0 and a closed switch represent binary 1.With this assignment we cannow represent any binary number. Figure 1-7(a) shows a binary code numberfor a garage door opener.The small switches are set to form the binary num-ber1000101010. The door will open only if a matching pattern of bits is setin the receiver and the transmitter.FIGURE 1-7 (a) Binarycode settings for a garagedoor opener. (b) Digitalaudio on a CD.(a)(b)Another example is shown in Figure 1-7(b), where binary numbers arestored on a CD. The inner surface (under a transparent plastic layer) iscoated with a highly reflective aluminum layer. Holes are burned throughthis reflective coating to form pits that do not reflect light the same as theunburned areas.The areas where the pits are burned are considered 1 andthe reflective areas are 0.There are numerous other devices that have only two operating states orcan be operated in two extreme conditions. Among these are: light bulb(bright or dark), diode (conducting or nonconducting), electromagnet (ener-gizedor deenergized), transistor (cut off or saturated), photocell (illumi-natedor dark), thermostat (open or closed), mechanical clutch (engaged ordisengaged), and spot on a magnetic disk (magnetized or demagnetized).In electronic digital systems, binary information is represented by voltages(or currents) that are present at the inputs and outputs of the various circuits.Typically, the binary 0 and 1 are represented by two nominal voltage levels.Forexample, zero volts (0 V) might represent binary 0, and 5 V might representbinary 1. In actuality, because of circuit variations, the 0 and 1 would be rep-resentedby voltage ranges.This is illustrated in Figure 1-8(a), where any volt-agebetween 0 and 0.8 V represents a 0 and any voltage between 2 and 5 Vrepresents a 1. All input and output signals will normally fall within one ofthese ranges, except during transitions from one level to another.We can now see another significant difference between digital and ana-logsystems. In digital systems, the exact value of a voltage is not important; 39. SECTION 1-5/DIGITAL CIRCUITS/LOGIC CIRCUITS 15Notused(a)5 V2 V0.8 V0 V0(b)Volts4 V1010 V tBinary 1Binary 0t0 t1 t2 t3 t4 t5InvalidvoltagesFIGURE 1-8 (a) Typical voltage assignments in digital system; (b) typical digitalsignal timing diagram.for example, for the voltage assignments of Figure 1-8(a), a voltage of 3.6 Vmeans the same as a voltage of 4.3 V. In analog systems, the exact value of avoltage is important. For instance, if the analog voltage is proportional to thetemperature measured by a transducer, the 3.6 V would represent a differenttemperature than would 4.3 V. In other words, the voltage value carries sig-nificantinformation. This characteristic means that the design of accurateanalog circuitry is generally more difficult than that of digital circuitry be-causeof the way in which exact voltage values are affected by variations incomponent values, temperature, and noise (random voltage fluctuations).Digital Signals and Timing DiagramsFigure 1-8(b) shows a typical digital signal and how it varies over time. It isactually a graph of voltage versus time (t) and is called a timing diagram.Thehorizontal time scale is marked off at regular intervals beginning at t0 andproceeding to t1, t2, and so on. For the example timing diagram shown here,the signal starts at 0 V (a binary 0) at time t0 and remains there until time t1.At t1, the signal makes a rapid transition (jump) up to 4 V (a binary 1). At t2,it jumps back down to 0 V. Similar transitions occur at t3 and t5. Note that thesignal does not change at t4 but stays at 4 V from t3 to t5.The transitions on this timing diagram are drawn as vertical lines, and sothey appear to be instantaneous, when in reality they are not. In many situ-ations,however, the transition times are so short compared to the times be-tweentransitions that we can show them on the diagram as vertical lines.Wewill encounter situations later where it will be necessary to show the transi-tionsmore accurately on an expanded time scale.Timing diagrams are used extensively to show how digital signals changewith time, and especially to show the relationship between two or more dig-italsignals in the same circuit or system. By displaying one or more digitalsignals on an oscilloscope or logic analyzer, we can compare the signals to theirexpected timing diagrams. This is a very important part of the testing andtroubleshooting procedures used in digital systems.1-5 DIGITAL CIRCUITS/LOGIC CIRCUITSDigital circuits are designed to produce output voltages that fall within theprescribed 0 and 1 voltage ranges such as those defined in Figure 1-8.Likewise, digital circuits are designed to respond predictably to input volt-agesthat are within the defined 0 and 1 ranges. What this means is that a 40. 16 CHAPTER 1/INTRODUCTORY CONCEPTSdigital circuit will respond in the same way to all input voltages that fallwithin the allowed 0 range; similarly, it will not distinguish between inputvoltages that lie within the allowed 1 range.To illustrate, Figure 1-9 represents a typical digital circuit with input viand output vo. The output is shown for two different input signal waveforms.Note that vo is the same for both cases because the two input waveforms,while differing in their exact voltage levels, are at the same binary levels.Digitalcircuitvivo0 V4 V0.5 V5 V0 Vt3.7 VtCase ICase II4 Vvi vovivo0 VFIGURE 1-9 A digitalcircuit responds to aninputs binary level (0 or 1)and not to its actualvoltage.Logic CircuitsThe manner in which a digital circuit responds to an input is referred to asthe circuits logic. Each type of digital circuit obeys a certain set of logicrules. For this reason, digital circuits are also called logic circuits. We willuse both terms interchangeably throughout the text. In Chapter 3, we willsee more clearly what is meant by a circuits logic.We will be studying all the types of logic circuits that are currently usedin digital systems. Initially, our attention will be focused only on the logicaloperation that these circuits performthat is, the relationship between thecircuit inputs and outputs.We will defer any discussion of the internal cir-cuitoperation of these logic circuits until after we have developed an un-derstandingof their logical operation.Digital Integrated CircuitsAlmost all of the digital circuits used in modern digital systems are inte-gratedcircuits (ICs).The wide variety of available logic ICs has made it pos-sibleto construct complex digital systems that are smaller and more reliablethan their discrete-component counterparts.Several integrated-circuit fabrication technologies are used to produce dig-italICs, the most common being CMOS, TTL, NMOS, and ECL. Each differs inthe type of circuitry used to provide the desired logic operation. For example,TTL (transistor-transistor logic) uses the bipolar transistor as its main circuit el-ement,while CMOS (complementary metal-oxide-semiconductor) uses the en-hancement-mode MOSFET as its principal circuit element.We will learn aboutthe various IC technologies, their characteristics, and their relative advantagesand disadvantages after we master the basic logic circuit types. 41. SECTION 1-6/PARALLEL AND SERIAL TRANSMISSION 17REVIEW QUESTIONS 1. True or false:The exact value of an input voltage is critical for a digital circuit.2. Can a digital circuit produce the same output voltage for different inputvoltage values?3. A digital circuit is also referred to as a ________ circuit.4. A graph that shows how one or more digital signals change with time iscalled a ________.1-6 PARALLEL AND SERIAL TRANSMISSIONOne of the most common operations that occur in any digital system is thetransmission of information from one place to another. The information canbe transmitted over a distance as small as a fraction of an inch on the samecircuit board, or over a distance of many miles when an operator at a com-puterterminal is communicating with a computer in another city. The infor-mationthat is transmitted is in binary form and is generally represented asvoltages at the outputs of a sending circuit that are connected to the inputsof a receiving circuit. Figure 1-10 illustrates the two basic methods for digi-talinformation transmission: parallel and serial.HMSBLSB01001000i01101001H00010010i10010110(a)LSB MSB LSB MSBFIGURE 1-10 (a) Paralleltransmission uses one con-nectingline per bit, and allbits are transmitted simul-taneously;(b) serial trans-missionuses only one sig-nalline, and the individualbits are transmitted serially(one at a time).(b)Figure 1-10(a) demonstrates parallel transmission of data from a com-puterto a printer using the parallel printer port (LPT1) of the computer. Inthis scenario, assume we are trying to print the word Hi on the printer.The 42. 18 CHAPTER 1/INTRODUCTORY CONCEPTSbinary code for H is 01001000 and the binary code for i is 01101001. Eachcharacter (the H and the i) are made up of eight bits. Using paralleltransmission, all eight bits are sent simultaneously over eight wires.The His sent first, followed by the i.Figure 1-10(b) demonstrates serial transmission such as is employedwhen using a serial COM port on your computer to send data to a modem, orwhen using a USB (Universal Serial Bus) port to send data to a printer. Al-thoughthe details of the data format and speed of transmission are quite dif-ferentbetween a COM port and a USB port, the actual data are sent in thesame way: one bit at a time over a single wire.The bits are shown in the dia-gramas though they were actually moving down the wire in the order shown.The least significant bit of H is sent first and the most significant bit of iis sent last. Of course, in reality, only one bit can be on the wire at any point intime and time is usually drawn on a graph starting at the left and advancingto the right.This produces a graph of logic bits versus time of the serial trans-missioncalled a timing diagram. Notice that in this presentation, the leastsignificant bit is shown on the left because it was sent first.The principal trade-off between parallel and serial representations is oneof speed versus circuit simplicity. The transmission of binary data from onepart of a digital system to another can be done more quickly using parallelrepresentation because all the bits are transmitted simultaneously, while se-rialrepresentation transmits one bit at a time. On the other hand, parallel re-quiresmore signal lines connected between the sender and the receiver ofthe binary data than does serial. In other words, parallel is faster, and serialrequires fewer signal lines. This comparison between parallel and serialmethods for representing binary information will be encountered manytimes in discussions throughout the text.REVIEW QUESTION 1. Describe the relative advantages of parallel and serial transmission ofbinary data.1-7 MEMORYWhen an input signal is applied to most devices or circuits, the output some-howchanges in response to the input, and when the input signal is removed,the output returns to its original state.These circuits do not exhibit the prop-ertyof memory because their outputs revert back to normal. In digitalcircuitry certain types of devices and circuits do have memory.When an inputis applied to such a circuit, the output will change its state, but it will remainin the new state even after the input is removed.This property of retaining itsresponse to a momentary input is called memory. Figure 1-11 illustrates non-memoryNonmemorycircuitMemorycircuitand memory operations.FIGURE 1-11 Comparisonof nonmemory and memoryoperation. 43. SECTION 1-8/DIGITAL COMPUTERS 19Memory devices and circuits play an important role in digital systems be-causethey provide a means for storing binary numbers either temporarily orpermanently, with the ability to change the stored information at any time. Aswe shall see, the various memory elements include magnetic and optical typesand those that utilize electronic latching circuits (called latches and flip-flops).1-8 DIGITAL COMPUTERSDigital techniques have found their way into innumerable areas of technol-ogy,but the area of automatic digital computers is by far the most notableand most extensive. Although digital computers affect some part of all of ourlives, it is doubtful that many of us know exactly what a computer does. Insimplest terms, a computer is a system of hardware that performs arithmeticoperations, manipulates data (usually in binary form), and makes decisions.For the most part, human beings can do whatever computers can do, butcomputers can do it with much greater speed and accuracy, in spite of the factthat computers perform all their calculations and operations one step at atime. For example, a human being can take a list of 10 numbers and find theirsum all in one operation by listing the numbers one over the other and addingthem column by column. A computer, on the other hand, can add numbersonly two at a time, so that adding this same list of numbers will take nine ac-tualaddition steps. Of course, the fact that the computer requires only a fewnanoseconds per step makes up for this apparent inefficiency.A computer is faster and more accurate than people are, but unlike mostof us, it must be given a complete set of instructions that tell it exactly whatto do at each step of its operation.This set of instructions, called a program,is prepared by one or more persons for each job the computer is to do. Pro-gramsare placed in the computers memory unit in binary-coded form, witheach instruction having a unique code.The computer takes these instructioncodes from memory one at a time and performs the operation called for bythe code.Major Parts of a ComputerThere are several types of computer systems, but each can be broken downinto the same functional units. Each unit performs specific functions, and allunits function together to carry out the instructions given in the program.Figure 1-12 shows the five major functional parts of a digital computer andData,informationArithmetic/logicInputControl OutputMemoryData,informationCentral ProcessingUnit (CPU)Control signalsData or informationFIGURE 1-12 Functional diagram of a digital computer. 44. 20 CHAPTER 1/INTRODUCTORY CONCEPTStheir interaction. The solid lines with arrows represent the flow of dataand information. The dashed lines with arrows represent the flow of timingand control signals.The major functions of each unit are:1. Input unit. Through this unit, a complete set of instructions and data isfed into the computer system and into the memory unit, to be stored un-tilneeded. The information typically enters the input unit from a key-boardor a disk.2. Memory unit. The memory stores the instructions and data received fromthe input unit. It stores the results of arithmetic operations received fromthe arithmetic unit. It also supplies information to the output unit.3. Control unit. This unit takes instructions from the memory unit one at atime and interprets them. It then sends appropriate signals to all theother units to cause the specific instruction to be executed.4. Arithmetic/logic unit. All arithmetic calculations and logical decisionsare performed in this unit, which can then send results to the memoryunit to be stored.5. Output unit. This unit takes data from the memory unit and prints out,displays, or otherwise presents the information to the operator (orprocess, in the case of a process control computer).Central Processing Unit (CPU)As the diagram in Figure 1-12 shows, the control and arithmetic/logic unitsare often considered as one unit, called the central processing unit (CPU).The CPU contains all of the circuitry for fetching and interpreting instruc-tionsand for controlling and performing the various operations called for bythe instructions.TYPES OF COMPUTERS All computers are made up of the basic units de-scribedabove, but they can differ as to physical size, operating speed, mem-orycapacity, and computational power, as well as other characteristics.Computer systems are configured in many and various ways today, with manycommon characteristics and distinguishing differences. Large computer sys-temsthat are permanently installed in multiple cabinets are used by corpo-rationsand universities for information technology support. Desktoppersonal computers are used in our homes and offices to run useful applica-tionprograms that enhance our lives and provide communication with othercomputers. Portable computers are found in PDAs and specialized comput-ersare found in video game systems. The most prevalent form of computerscan be found performing dedicated routine tasks in appliances and systemsall around us.Today, all but the largest of these systems utilize technology that hasevolved from the invention of the microprocessor. The microprocessor is es-sentiallya central processing unit (CPU) in an integrated circuit that can beconnected to the other blocks of a computer system. Computers that use amicroprocessor as their CPU are usually referred to as microcomputers. Thegeneral-purpose microcomputers (e.g., PCs, PDAs, etc.) perform a variety oftasks in a wide range of applications depending on the software (programs)they are running. Contrast these with the dedicated computers that are do-ingthings such as operating your cars engine, controlling your cars antilockbraking system, or running your microwave oven. These computers cannotbe programmed by the user, but simply perform their intended control 45. IMPORTANT TERMS 21task: they are referred to as microcontrollers. Since these microcontrollersare an integral part of a bigger system and serve a dedicated purpose, theyalso are called embedded controllers. Microcontrollers generally have all theelements of a complete computer (CPU, memory, and input/output ports), allcontained on a single integrated circuit.You can find them embedded in yourkitchen appliances, entertainment equipment, photocopiers, automaticteller machines, automated manufacturing equipment, medical instrumen-tation,and much, much more.So you see, even people who dont own a PC or use one at work or schoolare using microcomputers every day because so many modern consumerelectronic devices, appliances, office equipment, and much more are builtaround embedded microcontrollers. If you work, play, or go to school in thisdigital age, theres no escaping it: youll use a microcomputer somewhere.REVIEW QUESTIONS 1. Explain how a digital circuit that has memory differs from one that does not.2. Name the five major functional units of a computer.3. Which two units make up the CPU?4. An IC chip that contains a CPU is called a _____.SUMMARY1. The two basic ways of representing the numerical value of physical quan-titiesare analog (continuous) and digital (discrete).2. Most quantities in the real world are analog, but digital techniques aregenerally superior to analog techniques, and most of the predicted ad-vanceswill be in the digital realm.3. The binary number system (0 and 1) is the basic system used in digitaltechnology.4. Digital or logic circuits operate on voltages that fall in prescribed rangesthat represent either a binary 0 or a binary 1.5. The two basic ways to transfer digital information are parallelall bitssimultaneouslyand serialone bit at a time.6. The main parts of all computers are the input, control, memory, arith-metic/logic, and output units.7. The combination of the arithmetic/logic unit and the control unit makesup the CPU (central processing unit).8. A microcomputer usually has a CPU that is on a single chip called a mic-roprocessor.9. A microcontroller is a microcomputer especially designed for dedicated(not general-purpose) control applications.IMPORTANT TERMS*analog representationdigital representationdigital systemanalog systemanalog-to-digitalconverter (ADC)digital-to-analogconverter (DAC)decimal system*These terms can be found in boldface type in the chapter and are defined in the Glossary at the endof the book. This applies to all chapters. 46. 22 CHAPTER 1/INTRODUCTORY CONCEPTSbinary systembittiming diagramdigital circuits/logiccircuitsparallel transmissionserial transmissionmemorydigital computerprograminput unitmemory unitcontrol unitarithmetic/logic unitoutput unitcentral processingunit (CPU)microprocessormicrocomputermicrocontrollerPROBLEMSSECTION 1-21-1.*Which of the following are analog quantities, and which are digital?(a) Number of atoms in a sample of material(b) Altitude of an aircraft(c) Pressure in a bicycle tire(