ME3241 tokheim 8thed digital electronics principles and Applications(BookZZ org)

Differentiate between digital and analog signals, and identify the HIGH and LOW portions of a digital waveform.. Understand the definitions of HIGH, LOW, and undefined when observing

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"~Connect

\:h Learn

J Succeed"'

DIGITAL ELECTRONICS: PRINCIPLES AND APPLICATIONS, EIGHTH EDITION

Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY, 10020 Copyright© 2014 by The McGraw-Hill Companies, Inc All rights reserved Printed in the United States of America Previous editions© 2008, 2003, and 1999 No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning

Some ancillaries, including electronic and print components, may not be available to customers outside the United States

This book is printed on acid-free paper

www.mhhe.com

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Contents

Editor's Foreword viii

Preface ix

Acknowledgments xi

Walkthrough xii

About the Author xiv

Safety xv

Chapter l Digital Electronics 1-1 What Is a Digital Signal? 2

1-2 Why Use Digital Circuits? 4

1-3 Where Are Digital Circuits Used? 7

1-4 How Do You Generate a Digital Signal? 8

1-5 How Do You Test for a Digital Signal? 15

1-6 Simple Instruments 19

Summary 23

Chapter Review Questions 23

Critical Thinking Questions 25

Answers to Self-Tests 26

Chapter 2 Numbers We Use in Digital Electronics 27 2-1 Counting in Decimal and Binary 27

2-2 Place Value 28

2-3 Binary to Decimal Conversion 30

2-4 Decimal to Binary Conversion 30

2-5 Electronic Translators 31

2-6 Hexadecimal Numbers 34

2-7 Octal Numbers 36

2-8 Bits, Bytes, Nibbles and Word Size 37

Summary 39

Chapter 3 Logic Gates 43 3-1 The AND Gate 43

3-2 The OR Gate 46

3-3 The Inverter and Buffer 48

3-4 The NAND Gate 50

3-5 The NOR Gate 51

3-6 The Exclusive OR Gate 53

3-7 The Exclusive NOR Gate 54

3-8 The NAND Gate as a Universal Gate 56

3-9 Gates with More Than Two Inputs 57

3-10 3-11 3-12 3-13 3-14 3-15 3-16 Using Inverters to Convert Gates 59

Practical TTL Logic Gates 62

Practical CMOS Logic Gates 65

Troubleshooting Simple Gate Circuits 69

IEEE Logic Symbols 72

Simple Logic Gate Applications 73

Logic Functions Using Software (BASIC Stamp Module) 77

Summary 82

Chapter 4 Combining Logic Gates 90 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12 4-13 4-14 4-15 4-16 Constructing Circuits from Boolean Expressions 91

Drawing a Circuit from a Maxterm Boolean Expression 92

Truth Tables and Boolean Expressions 93

Sample Problem 97

Simplifying Boolean Expressions 99

Karna ugh Maps 100

Karnaugh Maps with Three Variables 101

Kamaugh Maps with Four Variables 103

More Karnaugh Maps 104

A Five-Variable Karna ugh Map 105

Using NAND Logic 106

Computer Simulations: Logic Converter 108

Solving Logic Problems: Data Selectors 112

Programmable Logic Devices (PLDs) 116

Using De Morgan's Theorems 124

Solving a Logic Problem (BASIC Stamp Module) 126

Summary 131

Chapter 5 IC S~ecifications and Simple Interfacing 141 5-1 Logic Levels and Noise Margin 141

5-2 Other Digital IC Specifications 146

5-3 MOS and CMOS ICs 150

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5-4 Intetlacing TIL and CMOS with Switches 152

5-5 Intetlacing TTL and CMOS with LEDs 156

5-6 Intetlacing TTL and CMOS ICs 160

5-7 Intetlacing with Buzzers, Relays, Motors, and Solenoids 164

5-8 Optoisolators 167

5-9 Intetlacing with Servo and Stepper Motors 170

5-10 Using Hall-Effect Sensors 178

5-11 Troubleshooting Simple Logic Circuits 185

5-12 Intetlacing the Servo (BASIC Stamp Module) 186

Summary 189

Chapter 6 Encoding, Decoding, and Seven-Segment Displays 196 6-1 The 8421 BCD Code 196

6-2 The Excess-3 Code 198

6-3 The Gray Code 199

6-4 The ASCII Code 202

6-5 Encoders 204

6-6 Seven-Segment LED Displays 205

6-7 Decoders 208

6-8 BCD-to-Seven-Segment Decoder/Drivers 209

6-9 Liquid-Crystal Displays 213

6-10 Using CMOS to Drive an LCD Display 218

6-11 Vacuum Fluorescent Displays 221

6-12 Driving a VF Display 224

6-13 Troubleshooting a Decoding Circuit 227

Summary 229

Chapter 7 Flip-Flops 236 7-1 The R-S Flip-Flop 236

7-2 The Clocked R-S Flip-Flop 239

7-3 The D Flip-Flop 241

7-4 The J-K Flip-Flop 243

7-5 IC Latches 247

7-6 Triggering Flip-Flops 249

7-7 Schmitt Trigger 251

7-8 IEEE Logic Symbols 252

7-9 Application: Latched Encoder-Decoder System 254

Summary 257

v1 Contents Chapter 8 Counters 262 8-1 Ripple Counters 262

8-2 Mod-10 Ripple Counters 264

8-3 Synchronous Counters 265

8-4 Down Counters 267

8-5 Self-Stopping Counters 269

8-6 Counters as Frequency Dividers 270

8-7 TTL IC Counters 272

8-8 CMOS IC Counters 276

8-9 A Three-Digit BCD Counter 280

8-10 Counting Real-World Events 284

8-11 Using a CM OS Counter in an Electronic Game 288

8-12 Using Counters-An Experimental Tachometer 291

8-13 Troubleshooting a Counter 295

Summary 298

Chapter 9 Shift Registers 305 9-1 Serial-Load Shift Registers 307

9-2 Parallel-Load Shift Registers 308

9-3 A Universal Shift Register 311

9-4 Using the 74194 IC Shift Register 313

9-5 An 8-Bit CMOS Shift Register 315

9-6 Using Shift Registers: Digital Roulette 318

9-7 Troubleshooting a Simple Shift Register 323

Summary 325

Chapter l 0 Arithmetic Circuits 330 10-1 10-2 10-3 10-4 10-5 10-6 10-7 Binary Addition 330

Half Adders 332

Full Adders 333

3-Bit Adders 335

Binary Subtraction 336

Parallel Subtractors 338

IC Adders 340

10-8 Binary Multiplication 343

10-9 Binary Multipliers 345

10-10 2s Complement Notation, Addition, and Subtraction 348

10-11 2s Complement Adders/Subtractors 353

10-12 Troubleshooting a Full Adder 355

Summary 357

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i2

4

5

7

Chapter 11 Memories 361 11-1 11-2 11-3 11-4 11-5 11-6 11-7 Overview of Memory 362

Random-Access Memory (RAM) 365

Static RAM ICs 367

Using a SRAM 370

Read-Only Memory (ROM) 372

Using a ROM 375

Programmable Read-Only Memory [PROM] 377

11-8 Nonvolatile Read/Write Memory 381

11-9 Memory Packaging 384

11-10 Computer Bulk Storage Devices 387

11-11 Digital Potentiometer: Using NV Memory 394

Summary 398

Chapter 12 Simple Digital Systems 403 12-1 Elements of a System 403

12-2 A Digital System on an IC 406

12-3 Digital Games 407

12-4 The Digital Clock 412

12-5 The LSI Digital Clock 415

12-6 The Frequency Counter 419

12-7 An Experimental Frequency Counter 423

12-8 LCD Timer with Alarm 426

12-9 Simple Distance Sensing 432

12-10 JTAG/Boundary Scan 437

Summary 441

Chapter 13 Computer Systems 445 13-1 The Computer 445

13-2 The Microcomputer 447

13-3 Microcomputer Operation 450

13-4 Microcomputer Address Decoding 454

13-5 Data Transmission 457

13-6 Detecting Errors in Data Transmissions 461

13-7 Data Transmission in a Computer System 464

13-8 Programmable Logic Controllers (PLCs) 469

13-9 Microcontrollers 473

13-10 The BASIC Stamp Microcontroller Modules 4 7 5 13-11 Digital Signal Processing 482

13-12 DSP in a Digital Camera 486

13-13 Microcontroller: Photo Input and Servo Motor Output 488

Summary 493

Chapter 14 Connecting with Analog Devices 499 14-1 DI A Conversion 500

14-2 Operational Amplifiers 501

14-3 A Basic DIA Converter 502

14-4 Ladder-Type DI A Converters 504

14-5 An AID Converter 506

14-6 Voltage Comparators 508

14-7 An Elementary Digital Voltmeter 510

14-8 Other AID Converters 512

14-9 AID Converter Specifications 516

14-10 An AID Converter IC 517

14-11 Digital Light Meter 520

14-12 Digitizing Temperature 523

Summary 525

Appendix A Appendix B Solder and the Soldering Process 530

2s Complement Conversions 535

Glossary of Terms and Symbols 536

Credits 549

Index 550

l ' '

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Editor's Foreword

The McGraw-Hill Education Trade and Technology list

has been designed to provide entry-level competencies in

a wide range of occupations in the electrical and

electron-ics fields It consists of coordinated instructional

mate-rials designed especially for career-oriented students A

textbook, an experiments manual, and online resources

support each major subject area covered in the series All

of these focus on theory, practice, applications, and

expe-riences necessary for those preparing to enter technical

careers

There are two fundamental considerations in the

prepa-ration of a text like Digital Electronics: Principles and

Applications: the needs for the learner and the needs of

the employer This text meets those needs in expert

fash-ion The authors and editors have drawn upon their broad

teaching and technical experiences to accurately interpret

and meet the needs of the student The needs of business

and industry have been identified through personal

inter-views, industry publications, government occupational

trend reports, and reports by industry associations

The processes used to produce and refine the series

have been ongoing Technological change is rapid, and

the content has been revised to focus on current trends

Refinements in pedagogy have been defined and

imple-mented based on classroom testing and feedback from

students and instructors using the series Every effort has

been made to offer the best possible learning materials These include animated PowerPoint presentations, circuit files for simulation, a test generator with correlated test banks, dedicated websites for both students and instruc-tors, and basic instrumentation labs All of these are well coordinated and have been prepared by the author The widespread acceptance of Digital Electronics: Prin- ciples and Applications and the positive feedback from users confirm the basic soundness in content and design of all the components as well as their effectiveness as teach-ing and learning tools Instructors will find the texts and manuals in each of the subject areas logically structured, well paced, and developed around a framework of modern objectives Students will find the materials to be readable, lucidly illustrated, and interesting They will also find a generous amount of self-study materials, review items, and examples to help them determine their own progress Both the initial and ongoing success of this text and others with the McGraw-Hill Trade and Technology list are due in large part to the wisdom and vision of Gordon Rockmaker, who was a magical combination of editor, writer, teacher, electrical engineer, and friend The pub-lisher and editor welcome comments and suggestions from instructors and students using this series

Charles A Schuler, Project Editor

Basic Skills 1n EIBctricity and EIBctronics

Charles A Schuler, Project Editor

New Editions in This Series

Electronics: Principles and Applications, Eighth Edition, Charles A Schuler

Editor's Foreword

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Preface

Digital Electronics: Principles and Applications, eighth

edition, is an easy-to-read introductory text for

stu-dents new to the field of digital electronics Providing

entry-level knowledge and skills for a wide range of

occupations is the goal of this textbook and its

ancil-lary materials Prerequisites are general math and

intro-ductory electricity/electronics Binary math, Boolean

concepts, simple programming, and various codes are

introduced and explained as needed Concepts are

con-nected to practical applications, and a systems approach

is followed that reflects current practice in industry

Earlier editions of the text have been used successfully

in a wide range of programs: electronic technology,

electrical trades and apprenticeship training, computer

repair, communications electronics, and computer

sci-ence, to name a few This concise and practical text can

be used in any program needing a quick and readable

overview of digital principles

New to this Edition

Chapter 1

• Digital applications, including automotive fuel

in-dicators, vehicle speed sensors, and engine control

module

• A new section on where digital circuit applications

are used

• Information on logic probe use in troubleshooting

• A revised instruments section

Chapter 2

• Subsection on applications of encoders and

decoders

Chapter 3

• Updated information on practical chips including

lower voltage ICs

• Expanded most self-test sections

Chapter4

• Expanded several self-test sections

• Revised material on data selectors

Chapter 5

• Information on low-voltage ICs

• Added many application assignments on interfacing Chapter 6

• Updated applications of the Gray code, including the shaft encoder, and new information on the quadrature encoder

• Updated information on display technologies Chapter7

• Expanded several self-tests

• Updated binary subtraction section

Chapter 11

• Updated overview of memory section

• Updated nonvolatile read/write memory section

• Updated memory packaging section

• Expanded bulk storage section, including more information on USB flash drives

• Internet research topics

Chapter 12

• Expanded self-test and critical thinking questions

• Information on distance sensing with coverage of several sensor technologies

• A DIY application demonstrating a distance sensor triggering the timed operation of a stepper motor Chapter 13

• Updated microcomputer section

• Updated data transmission section

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• A revised microcontrollers section

• Application of a microcontroller with photo input

and servo motor output

Chapter 14

• Expanded self-test questions

Additional Resources

An Experiments Manual for Digital Electronics contains

a comprehensive test, a variety of hands-on lab exercises

and experiments, and additional problems for each

chap-ter in the textbook

The Online Learning Center (OLC) at www.mhhe

com/tokheim8e includes comprehensive Multisim files,

keyed to circuits found in the eighth edition, and a Multisim

primer (written by Patrick Hoppe of Gateway Technical

College), which provides a tutorial on the software for new

users The Multisim program itself is not included on the

website, but the latest version, version 12, can be purchased through McGraw-Hill at a discount when you adopt this

textbook Visit www.mhhe.com/tokheim8e or contact your

McGraw-Hill sales representative for more information The OLC also features chapter study resources, links to industry and association sites, and assignments and tests for students Instructors can access the instructor side of the OLC to find a wide selection of information including:

• An Instructor's Manual that includes a list of the parts and equipment needed to perform lab experi-ments, learning outcomes for each chapter, answers

to chapter review questions and problems, and more

• PowerPoint presentations that correlate to all ters and special PowerPoint presentations on bread-boarding, soldering, circuit interrupters (GFCI and AFCI), and instrumentation

chap-• A test generator, EZ Test, which includes a test bank with questions for each chapter

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cknowledgments

Thanks to family members Marshall, Rachael, Dan, Jack,

Ben and Carrie for their help on this project I would also

like to thank the reviewers who helped evaluate the

text-book; I am grateful for their time and expertise

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alkthrough

Digital Electronics: Principles and Applications, eighth

edition, is designed for a first course in digital

electron-ics It provides a concise, modern, and practical approach

that's suitable for a range of electricity and electronics

XII

Learning Outcomes

Tflix chapter will hdp yo11 m:

1·1 fdr1u1/y ,, ,,er;tl dwr.ic1eri<lk.'i of di,sir.d

cin:uitsa>oppo o.J1o:m.1hP;dn:uil>

/Ji{f<'mllit11eb.:t"ccndi~it~J and;1n.1!oi;

.<ii;11:11.•, :ind ide111if1· 1nc HIGH aml LOW

portionsnfa<ligi1atw·.1vcform

1·2 Cluuifv the <ignah (analog; or digil~h in

>c -er~l "PPlk~tion circuit< 1111"/.r~c the

op.:r~tion uf\Cvcr 11 !iq ,id·rnca.wrinJ,!

cin:ui1~ £11•frii1111hycomcninga0Jfog

inpol~fcum:n1<:1nJ,·ol!agts)from.<';Cll,Ots

todigi1~1 fonn c~n Ix: u;:.:ful

1-3 Li.•f :1·cr~I cununon pi~-.:.:.~ofclcctronic

:;c-~r that ;on1ai11 <lig•!~l dn:uitry Oi1c1m

circ\lit> fll/rrprerlngie probe readings

durtns !~ ,,1ing ofadii;ical circuit

E~f~~~~; a~g~~f~~ 11 ~it~~~~~~:io: 1 ~~trSi~ii~

tal in nawre Historically most electronic pnxlucls contained a.irnlog circuitry Most newly designed electronic devices rn111ain digit:il circuitry This chapter introduces you to the world of digital electronics

uct n111rai11.1· di&iWl drr.uirry? Signs that n device contains digital circuitry indude:

What:iretheduesr.h;itnnelectronicprod-I Doe~ it have a disphiy that shows numbers, letters pictures, or video?

2 Docs it have a memory or can it More information?

3 C;m the dc\•icc he programmed'!

4 C;in it he conncc!e<l l(1 the ln1cmc1?

If the answer to any one of the four tions is yes then the product probably contains digital circuitry

ques-Digital circuitry is quickly hecoming pe1vasive because of its ad1'antagc.1 over

Key terms are carefully defined and explained

in the text and listed in the margins so students

can easily identify them

~· A(n) _ _ _ (anl;llog, digi1al) di:vicc

i.\Onc that hasa.~ignalwhichvariescon·

tinuouslyin~tepwith!hcinput

3 Refer to Fig l-4 The input to the elecmmicblock iseta.~siliedasn(n) _ _ _ (analog, digiiall signal

4 Refert0Fig l-4.Theo11tpmfromthe efcetronic hlock i~ ctu.,silied a~ a(n) _ _ _ (analog, digital) sign;iJ

5 An annlog circuit is one that procc~$C$

analogsignalswhileadigitalcircuit proccsses _ _ ~ignals

full-Each chapter begins with a list of learning outcomes that tell the reader what he or she

should expect to accomplish by the end of the chapter The outcomes are tied to the chapter subsections

Huadecimal num!rersymm Buel6system He.aidecimi!

natatian Mii;ral'rucnstJr·

and F and is 1cfcrrcd to a~ the fxni• 16 .<y1IL'lll

Figure 2-9 ~how.~ the equivalent bin~ry and hexadecimal representations for the decim;il for decimal IO "B~ for decimal IL and ~o on

The adv;inlage ut the hc:irndccimal sy,,tcm is it~

u1><!Fulne.,~ in converting directly from a 4-hit binary number For instance hexadcdm~! F

~tand~ for the -l·bit binary number l 11 ! He.w·

detima/ 11111Uti1111 is typically ug."d to repre~cnt

;i binary number For in~tancc, the hexadecimal number A6 y.uuld rcprc ent the 8·bit binary

number !UJUOl IU Hexudcc1mal notatmn is

widely usi:d in micmprocc.uor-lm.1t:d f_Y\tt.'1111

to repre.\Cnt 4 8- !6-, 32·, or 6-1-·hit binary numbers

The numhcr lO rt:prc).Cnh how many ob·

jcct~·! It can he oh~crved from the table ~hown

in Fig 2-9 that the number IOcouldmc:m ten ohjccts, two nhjt.-Cb or ~ixtee11 objects depend· ing on the ba~c of the number Subsuipfl arc

~omctimes :iddcd to a number to indicate the ba.~e of the numh-::r U~ing \Ub?>Cripts, !he number 10"' repre,1,cnts ten object~ The subscript {IOinthisexample) indic;itcsit isalwfc JO.or decimal number U~ing ~uthcripl\, thc number

10, reprerent.~ two objects since this is in binary

(bi11e 2) Again u~ing suhscripls the number

The self-tests can either help students

identify areas that need further study or serve as positive reinforcement for material that students already know After completing

a self-test, students may check their answers

in the Answers to Self-Tests sections at the

end of each chapter

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A photographic hls!ory of the computer One ot the first computers was the Eniac (upper felt), devel·

oped in the 1940s The 1970s marked the expanded use of the computer by busmesses The

main-frame computer (uppernght) was the 100101 the time Jn the 1980s persona! computers such as the

Apple l!e (lower left) brought computers intn our homes and sehools Today, perS-Onal computers can

goanywtiere,aslaptopcomputers(lowertighl}increaselnpopu!arity

A Changing Acid E!ei:tmn!cs Is among Ille most exciting lxritd ;1 prototype (1r troublc)horJI and rcp;iir

:ire as of technical s!udy New developments are reported digital analog:, nnd combined ~y~tcm-

weekly lnterestiogly, m-OSt dtwelopments are based on the Anulogd.:1111111ic 11·1t<:m\ haw been popular

c\prcs,ion to it' m11nem1 form Conver ion~

twm maxt1:rm-to·111intern1 or minterm-to-ma,

lt:rmforin,u'l!co111u1onlyumkrt;ikentogc1rid

of Jong overh:1r~ in the Buoleln c'p1c~,io11

rhe new e:umple iJlu,trated in Fi!! 4-46 will change the ma~tern1 e:tprc ,ion (A + 8 + (;} · (;r:;:s-+c) = Yto i1~ mime1m equivalent :md dim111;uethelongoverbar.Carcful!yfollow1he comer:.ion procc , in Fi!!- 4-~ The re~u!t of thhcun\Cr.>itJn)iclJ,th<: iuinccnu IU1mA B

C + A B -C = Y which p.:rfonm C:.'<lt:t!y the

\3mc kl\!k fm1<:uo11 a~ the m;J.:tlt:rrn expn::~sion

!A+B + Cl ( l + + 0 = Y The re~ulting

rnm1ermcxpres.,ioncanhewrmen inconven·

t\lmJJ form :1.~A B · C +A· fl C= Yu,\n!!

O\'t:r!iJr: or in !he 'h\lftcncd kcybourd vefliio~

ABC+ A'B·c = Yu.,ing <!po~trophes

Jt mu~t hc undcr~too<l that the logic db·

grnm< that ""ould hc wird U'>ing the maxtern1

matfle-1850, Ge<lrge &Joie created Booteana!gebra,whidlunderlies thetheoryoflogrc

fundamentals !earned in the first classes in elettrlcity, :ma1og in the ~ 1 ,1 Okkr TV> telephones and auiomo·

1·2 Why Use Digital Circuits?

Electronic~ Ue,ignct'i and technicians must

huvc a v.mldng knowledge of both analog and

digital \Y~tem~ The de~igncr mint <ledde if the

~y~tem will ul.( an:1!og or digital technique~ or

in ~omc milit;iry applications such as tire con·

tro!oo.\hip.>

Mo)t rcal·wnrld inforrnulion is mw/og in nature NJtural phenomena, ~uch a.> time, temperature lrnmidicy wind ~peed r;idia- tion ani.J sound inten,ity :ire :ma lug in nature You proh;ib!y have ;ilrc;idy mea$1ircd voltage,

Digital Circuitry: Advontoges

and limitotions

Some of the :idvanwgc\ ror u~ing dii;'1tal cir·

cuitry lnJ.!ead of anal0<,; arc nJ !bllow':

l lnexpcn~ive IC~ can be u:-cd with few

extcrn;ilcomponent.\

lnfounaci,1ncanbc\torcdfor,hort

pt!rioclsorinJelinitdy

J Darn can he u~ for prt:cbe t:a!cubtion'

4 Systems can be de~igned more e:i -ily

u,Jng conipaiihk digital logic familie.~

5 Systems cm1 be programmed and ~how

Mime manrr.:r ol "intclllgencc"

6 Al?hnnumeric,picture,and video

7 Digi1al dri:uib are !c~' uffix:ied by unwanted de<.:uic:1tinteikn::ocet":l!b.J11(1i1e

8 Suchcircuitsarecompaub!ewith the lmern1:tnn<lcomputc1~, The limi/(/f/flll\ oj diir;1tal cirnii11y are :I.\

follow~:

! Mo.'l re~!-WDfld ewnl\ are ~na!n•3" in nature

2 An;i!og pnlee~sing h U\u;1!!y 'impler and fa.-ier

Digital circuic~ a1e ;ipp.::aring in rnurc and more product.~ primarily bec;iu~ of low-co~t

reliable digital JC~ Other n:a~on' for their growing popularity arc ac1:uracy added \tll·

hilitv comouler commuibilitv mcmocv, ea;.c

Critical facts and principles are reviewed in

the Summary and Review section at the end

of each chapter

~ ;.: -Internet connections encourage students to

do online research on certain topics

Chapter l Summary and Review

L Analog signals vary gradually and continuou~ly

while digital ignah produce dhcrete \·oltngt:

lcveh commouly refcned to a\ HIGH and LOW

2 Mo-.t modern electronic equipment contain.\ both analoganddigitalcircuilry

3 Logic tcve!sJrediffen:nt forvariou,digital logic fnmilics, such as 1TL and CMOS These logic lcvt'b an:: t'Qmmonly referred to as HIGH, LOW

and undefined Figure 1-20 Uewih the;.c TIL nnd

6_ Digilalclectrooicsi~ a huge 3nd rapidly e.,p:in<ling field Digital computen in all their fom1s, serve :i.~

ihelrn:lhoncofthe fnh:met

7 Bbt'1.ble, mono,1ah!c, 30d a.~table rnultivibrntors Jn: ut.ed 10 !;!enerate digital ~ignah Thc\C are MHnctune~ca11ed la1che.~.onc·~ho1, ;ind Cree·

runningmultivibr.ito1Ji,rt:~peetively

8 Logic kvd indic:m}fs may toke the tv1m of ~imp!e

LE.D ;ind ~i,tor drcuits, ~ollmrten, or logic probes

f11181818181D!mR!E!llBRl:ll•••••1""'1 -!f-Chapter review questions are found at the end of

2-J I Convert the bin;uy number in a to d 10

2-17 An 8-bit g1oupof h:ind Os which reprc::cm~;i

number letter, or op code, b commonly cJIJed a

_ _ _ fbyte.nihbkJ

2-1 !(the digital circuiL~ in a computer only respond

to tiinary nuinher.;, why are ocrnl an<l

he.,a-decimal number~ used exten~ively by computer

spe-.:i3lisi~·!

2-2 Jn a digital sy~tem ,uch a.' a mlCH\COmP'Jler, it

is common to consider an S-bit l!roup (called

2·18 A nibbleisatermthatdei:cribe~a _ _ _ (4-bit, 12-btt)datagroup

2· 19 Mieroptoce~~or-h3 ed ~yMems {~uch a.~ a pulef) commonly identify the size or o d;ua gT0Up3~ -(fi!e.WOfd)!ength

com-2·20 To encrypt data from a readable form (~uch a~ alphanumeric) to m:ichinc code u.<.able by digital r:in:uits is called _ _ _ (encoding, interr~ing)

2-4 Al the op¢ ion of your instructor, U!>C circuit slmu!;itioo art ware to (a) draw the logic dia·

gram of the binary-to-<lecimal decoder circuit

~hown 'rn Fig 2-18, (b) opernce the circuit, and (el dcrnonsuate the bin:iry·to-decirnal decoder simufotiontoyourinstructor

each chapter, as are critical thinking questions

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bout the uthor

Over several decades, Roger L Tokheim has published

many textbooks and lab manuals in the areas of

digi-tal electronics and microprocessors His books have

xiv About the Author

been translated into nine languages He taught technical subjects including electronics for more than 35 years in public schools

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Safety

Electric and electronic circuits can be dangerous Safe

practices are necessary to prevent electrical shock, fires,

explosions, mechanical damage, and injuries resulting

from the improper use of tools

Perhaps the greatest hazard is electrical shock A

cur-rent through the human body in excess of 10

milliam-peres can paralyze the victim and make it impossible

to let go of a "live" conductor or component Ten

mil-liamperes is a rather small amount of current flow: It

is only ten one-thousandths of an ampere An ordinary

flashlight can provide more than 100 times that amount

of current!

Flashlight cells and batteries are safe to handle

be-cause the resistance of human skin is normally high

enough to keep the current flow very small For

exam-ple, touching an ordinary 1.5-V cell produces a current

flow in the microampere range (a microampere is

one-millionth of an ampere) The amount of current is too

small to be noticed

High voltage, one the other hand, can force enough

current through the skin to produce a shock If the

cur-rent approaches 100 milliamperes or more, the shock can

be fatal Thus, the danger of shock increases with

volt-age Those who work with high voltage must be properly

trained and equipped

When human skin is moist or cut, its resistance to the

flow of electricity can drop drastically When this

hap-pens, even moderate voltages may cause a serious shock

Experienced technicians know this, and they also know

that so-called low-voltage equipment may have a

high-voltage section or two In other words, they do not

prac-tice two methods of working with circuits: one for high

voltage and one for low voltage They follow safe

proce-dures at all times They do not assume protective devices

are working They do not assume a circuit is off even

though the switch is in the OFF position They know the

switch could be defective

Even a low-voltage, high-current-capacity system

like an automotive electrical system can be quite

dangerous Short-circuiting such a system with a ring

or metal watchband can cause very severe

burns-especially when the ring or band welds to the points

being shorted

As your knowledge and experience grow, you will learn many specific safe procedures for dealing with elec-tricity and electronics In the meantime:

1 Always follow procedures

2 Use service manuals as often as possible They often contain specific safety information Read, and comply with, all appropriate material safety data sheets

3 Investigate before you act

4 When in doubt, do not act Ask your instructor or supervisor

General Safety Rules for Electricity and Electronics

Safe practices will protect you and your fellow workers Study the following rules Discuss them with others, and ask your instructor about any you do not understand

1 Do not work when you are tired or taking medicine that makes you drowsy

2 Do not work in poor light

3 Do not work in damp areas or with wet shoes or clothing

4 Use approved tools, equipment, and protective devices

5 Avoid wearing rings, bracelets, and similar metal items when working around exposed electric circuits

6 Never assume that a circuit is off Double-check it with an instrument that you are sure is operational

7 Some situations require a "buddy system" to antee that power will not be turned on while a tech-nician is still working on a circuit

guar-8 Never tamper with or try to override safety devices such as an interlock (a type of switch that automati-cally removes power when a door is opened or a panel removed)

9 Keep tools and test equipment clean and in good working condition Replace insulated probes and leads at the first sign of deterioration

10 Some devices, such as capacitors, can store a lethal

charge They may store this charge for long periods

Trang 16

of time You must be certain these devices are

dis-charged before working around them

11 Do not remove grounds and do note use adaptors

that defeat the equipment ground

12 Use only an approved fire extinguisher for electrical

and electronic equipment Water can conduct

elec-tricity and may severely damage equipment Carbon

dioxide (C02) or halogenated-type extinguishers

are usually preferred Form-type extinguishers may

also be desired in some cases Commercial fire

ex-tinguishers are rated for the type of fires for which

they are effective Use only those rated for the

proper working conditions

13 Follow directions when using solvents and other

chemicals They may be toxic, flammable, or may

damage certain materials such as plastics Always

read and follow the appropriate material safety data

sheets

14 A few materials used in electronic equipment are

toxic Examples include tantalum capacitors and

be-ryllium oxide transistor cases These devices should

not be crushed or abraded, and you should wash

your hands thoroughly after handling them Other

materials (such as heat shrink tubing) may produce

irritating fumes if overheated Always read and low the appropriate material safety data sheets

fol-15 Certain circuit components affect the safe mance of equipment and systems Use only exact or approved replacement parts

perfor-16 Use protective clothing and safety glasses when handling high-vacuum devices such as picture tubes and cathode-ray tubes

17 Don't work on equipment before your know proper procedures and area aware of any potential safety hazards

18 Many accidents have been caused by people ing and cutting corners Take the time required to protect yourself and others Running, horseplay, and practical jokes are strictly forbidden in shops and laboratories

rush-19 Never look directly into light-emitting diodes or fiber-optic cables; some light sources, although in-visible, can cause serious eye damage

Circuits and equipment must be treated with respect Learn how they work and the proper way of working on them Always practice safety: your health and life depend

on it

Electronics workers use specialized safety knowledge

xvi Safety

Trang 17

learning Outcomes

This chapter will help you to:

1-1 Identify several characteristics of digital

circuits as opposed to analog circuits

Differentiate between digital and analog

signals, and identify the HIGH and LOW

portions of a digital waveform

1-2 Classify the signals (analog or digital) in

several application circuits Analyze the

operation of several liquid-measuring

circuits Explain why converting analog

inputs (currents and voltages) from sensors

to digital form can be useful

1-3 List several common pieces of electronic

gear that contain digital circuitry Discuss

the demand for computer and electronics

technicians, and identify training

opportunities

1-4 List three types of multivibrators, and

describe how they generate types of digital

signals Analyze several multivibrator and

switch debouncing circuits

1-5 Analyze several logic-level indicator

circuits Interpret logic probe readings

during testing of a digital circuit

Understand the definitions of HIGH,

LOW, and undefined when observing logic

levels in both TIL and CMOS digital

What are the clues that an electronic

prod-uct contains digital circuitry? Signs that a

device contains digital circuitry include:

1 Does it have a display that shows numbers, letters, pictures, or video?

2 Does it have a memory or can it store information?

3 Can the device be programmed?

4 Can it be connected to the Internet?

If the answer to any one of the four tions is yes, then the product probably con-tains digital circuitry

ques-Digital circuitry is quickly becoming

pervasive because of its advantages over

analog including:

1 Generally, digital circuits are easier

to design using modem integrated circuits (ICs)

2 Information storage is easier to implement with digital

3 Devices can be made programmable with digital

4 More accuracy and precision are possible

5 Digital circuitry is less affected by unwanted electrical interference called noise

All persons working in electronics must have knowledge of digital electronic cir-cuits You will use simple integrated circuits and displays to demonstrate the principles

of digital electronics

Identifying digital products

Advantages af digital

Trang 18

1-1 V\Jhat Is a Digital Signal?

In your experience with electricity and ics you have probably used analog circuits The circuit in Fig 1-l(a) puts out an analog signal

electron-or voltage As the wiper on the potentiometer is moved upward, the voltage from points A to B

gradually increases When the wiper is moved downward, the voltage gradually decreases from 5 to 0 volts (V) The waveform diagram

in Fig 1-l(b) is a graph of the analog output On the left side the voltage from A to B is gradually increasing to 5 V; on the right side the voltacre

is gradually decreasing to 0 V By stopping the potentiometer wiper at any midpoint, we can get an output voltage anywhere between O and

5 V An analog device, then, is one that has a signal which varies continuously in step with the input

A digital device operates with a digital signal

Figure 1-2(a) pictures a square-wave generator

The generator produces a square waveform that

is displayed on the oscilloscope The digital nal is only at +5 V or at 0 V, as diagrammed in Fig l-2(b) The voltage at point A moves from

sig-0 to 5 V The voltage then stays at +5 V for a time At point B the voltage drops immediately from +5 to 0 V The voltage then stays at O V for a time Only two voltages are present in a digital electronic circuit In the waveform dia-gram in Fig l-2(b) these voltages are labeled

HIGH and LOW The HIGH voltage is +5 V;

the LOW voltage is 0 V Later we shall call the HIGH voltage (+5 V) a logical 1 and the LOW voltage (0 V) a logical 0 Circuits that handle only HIGH and LOW signals are called digital circuits

The digital signal in Fig 1-2(b) could also be generated by a simple on-off switch A digital signal could also be generated by a transistor turning on and off Digital electronic signals are usually generated and processed by inte-grated circuits (ICs)

Both analog and digital signals are sented in graph form in Figs 1-1 and 1-2 A

repre-signal can be defined as useful information transmitted within, to, or from electronic cir-cuits Signals are commonly represented as

a voltage varying with time, as they are in Figs 1-1 and 1-2 However, a signal could be

an electric current that either varies ously (analog) or has an on-off (HIGH-LOW)

continu-2 Chapter 1 Digital Electronics

1-1 (a) Analog output from a potentiometer

(b) Analog signal waveform

characteristic (digital) Within most digital circuits, it is customary to represent signals

in the voltage versus time format When digital circuits are interfaced with nondigi-tal devices such as lamps and motors, then the signal can be thought of as current versus time

The standard volt-ohm-millimeter (VOM) shown in Fig l-3(a) is an example of an analog measuring device As the voltage, resis-tance, or current being measured by the VOM increases, the needle gradually and continuously moves up the scale A digital multimeter

(DMM) is shown in Fig 1-3(b) This is an ample of a digital measuring device As the

ex-Square-wave generator 1 - _,a

·1-2 (a) Digital signal displayed on scope

(b) Digital signal waveform

8

HIGH

LOW

Trang 19

(a) (b) (a) Analog meter (6) Digital multimeter (DMM) Courtesy Fluke Corporation Reproduced with permission

current, resistance, or voltage being measured

by the DMM increases, the display jumps

up-ward in small steps The DMM is an example

of digital circuitry taking over tasks previously

Supply the missing word in each statement

1 Refer to Fig 1-2 The + 5-V level of the

_ _ _ _ (analog, digital) signal could

also be called a logical 1 or a _ _ _ _

(HIGH, LOW)

2 A(n) (analog, digital) device

is one that has a signal which varies

con-tinuously in step with the input

4 Refer to Fig 1-4 The output from the

electronic block is classified as a(n) _ _ _ _ (analog, digital) signal

5 An analog circuit is one that processes analog signals while a digital circuit

Trang 20

History of

Electronics

A photographic history of the computer One of the first computers was the Eniac (upper Jett),

devel-oped in the 1940s The 1970s marked the expanded use of the computer by businesses The

main-frame computer (upper right) was the tool of the time In the 1980s personal computers such as the Apple lie (lower left) brought computers into our homes and schools Today, personal computers can

go anywhere, as laptop computers (lower right) increase in popularity

areas of technical study New developments are reported

weekly Interestingly, most developments are based on the

fundamentals learned in the first classes in electricity, analog

and digital circuits, computer technology and robotics, and

communications

1-2 Why Use Digital Circuits'?

Electronics designers and technicians must have a working knowledge of both analog and digital systems The designer must decide if the system will use analog or digital techniques or

4 Chapter 1 Digital Electronics

a combination of both The technicians must build a prototype or troubleshoot and repair digital, analog, and combined systems

Analog electronic systems have been popular

in the past Older TVs, telephones, and biles featured analog circuits Before modern digital computers, analog computers were used

automo-in some military applications such as fire trol on ships

con-Most real-world information is analog in nature Natural phenomena, such as time, temperature, humidity, wind speed, radia-tion, and sound intensity, are analog in nature You probably have already measured voltage,

Trang 21

current, resistance, power, capacitance,

induc-tance, and frequency in other electricity and

electronics courses Other things to be

mea-sured include pressure, weight, oxygen (and

other gases), ultrasonic sound, acceleration

and tilt, vibration, direction (compass), global

positioning, proximity, magnetic fields, linear

distance, and angle of rotation (angular speed)

They are all analog in nature Engineers and

technicians commonly use sensors to measure

these things Many sensors emit an analog

signal

A simple analog electronic system for

mea-suring the amount of liquid in a tank is

illus-trated in Fig 1-5 The input to the system is a

varying resistance The processing proceeds

according to the Ohm's law formula, I = V/ R

The output indicator is an ammeter which is

calibrated as a water tank gauge In the analog

system in Fig 1-5 as the water rises, the input

resistance drops Decreasing the resistance R

causes an increase in current (/) Increased

cur-rent causes the ammeter (water tank gauge) to

read higher

Water tank

The analog system in Fig 1-5 is simple and efficient The gauge in Fig 1-5 gives an indica-tion of the water level in the tank If more infor-mation is required about the water level, then a digital system such as the one shown in Fig 1-6 might be used

Digital systems are required when data must

be stored, used for calculations, or displayed as numbers and/or letters A somewhat more com-plex arrangement for measuring the amount

of liquid in a water tank is the digital system shown in Fig 1-6 The input is still a variable resistance as it was in the analog system The resistance is converted into numbers by the

analog-to-digital (AID) converter The central processing unit (CPU) of a computer can ma-nipulate the input data, output the information, store the information, calculate things such as flow rates in and out, calculate the time until the tank is full (or empty) based on flow rates, and so forth Digital systems are valuable when calculations, data manipulations, data storage, and alphanumeric or video outputs are required

Data transfers via the Internet are common

Analog INPUT

Analog PROCESSING

Analog OUTPUT

% Fig 1-S Analog system used to interpret float level in water tank

Water tank

Analog Digital

~ INPUT

AID converter

Fig Hi Digital system used to interpret float level in water tank

1 = .!::'._ (constant)

R

STORAGE (memory)

PROCESSING

CPU and memory

I OUTPUT I

CRT or other digital display

Analog-ta-digital

(A/D) converter Central processing unit (CPU)

Trang 22

Ei

Application: Automobile Fuel Indicators

Older automobile circuitry was analog in ture Consider the traditional fuel gauge system sketched in Fig l-7(a) The fuel tank sending unit has a float that moves a wiper on a resistive ma-terial Increasing the fuel level in the tank raises the float, causing the wiper to move left on the resistor The resistor's value decreases Decreased circuit resistance causes an increase in current in

na-the series circuit (via Ohm's law, I= V/ R) The

in-creased current causes the needle on the fuel gauge (an ammeter) to move clockwise toward F on the meter face The older-style fuel gauge diagram in Fig l-7(a) is an example of an analog circuit

Newer automobiles may use the information from the fuel tank sending unit for several pur-poses Figure l-7(b) shows the analog voltage from the fuel tank sending unit entering the in-strument panel module The computer module converts the analog input to digital information

(AID converter) The computer module also

re-ceives signals from the vehicle speed sensor, engine control module (ECM) The input in-

formation is processed by the computer ule The instrument control module will drive

mod-a trmod-aditionmod-al-looking fuel gmod-auge locmod-ated on the instrument panel A tachometer is probably also located on the instrument panel With the inputs

It will be noted that information from the sensors in Fig l-7(b) comes in various forms

The fuel tank sending unit delivers a voltage signal to the computer module With

variable-higher levels of fuel in the tank the sending unit generates a higher positive voltage

The vehicle speed sensor sends a frequency signal At lower vehicle speeds the

variable-sensor emits a low-frequency signal At higher speeds a high-frequency signal is sent to the computer module

The engine control module sends several

digital signals to the instrument control

mod-ule The engine control module determines how much fuel is injected into the cylinders of the engine and the timing

Variable resistor

Fuel tank sending unit

(a)

OUTPUTS

Instrument panel

0

LCD dash display

(b)

Fig 1-7 [al A~tomobile fuel tank sending unit and fuel gauge (b) Modern automobile fuel

1nd1cator system with computer module

Chapter 1 Digital Electronics

Trang 23

Digital Circuitry: Advantages

and limitations

Some of the advantages for using digital

cir-cuitry instead of analog are as follows:

1 Inexpensive ICs can be used with few

external components

2 Information can be stored for short

periods or indefinitely

3 Data can be used for precise calculations

4 Systems can be designed more easily

using compatible digital logic families

5 Systems can be programmed and show

some manner of "intelligence."

6 Alphanumeric, picture, and video

information can be viewed using a variety

of electronic displays

Answer the following questions

6 Generally, electronic circuits are

classified as either analog o r

-7 Measurements of time, speed, weight,

pressure, light intensity, and position are

_ _ _ _ (analog, digital) in nature

8 Refer to Fig 1-5 As the water level

drops, the input resistance increases

This causes the current I to

-(decrease, increase) and the water level

gauge (ammeter) will r e a d

-(higher, lower)

9 Refer to Figs 1-5 and 1-6 If this water

tank were part of the city water system,

where rates of water use are important,

would be most appropriate

1-3 Where Are Digital Circuits

Used'?

Digital electronics is a huge and rapidly

ex-panding field The global system of

intercon-nected computer networks called the Internet

serves billions of users Digital computers, in

7 Digital circuits are less affected by unwanted electrical interference called noise

8 Such circuits are compatible with the Internet and computers

The limitations of digital circuitry are as follows:

1 Most real-world events are analog in nature

2 Analog processing is usually simpler and faster

Digital circuits are appearing in more and more products primarily because of low-cost, reliable digital ICs Other reasons for their growing popularity are accuracy, added sta-bility, computer compatibility, memory, ease

of use, simplicity of design, and compatibility with a variety of displays

10 True or false The most important son why digital circuitry is becoming more popular is that digital circuits are usually simpler and faster than analog circuits

rea-11 Refer to Fig 1-7(a) This traditional auto fuel tank gauge assembly that senses and indicates the fuel level is an example of a(n) (analog, digital) circuit

12 Refer to Fig l-7(b) The input voltage from the fuel tank sending unit is a digi-tal signal before it enters the instrument panel module (T or F)

13 Refer to Fig l-7(b) The input from the enaine control module (ECM) having to I:>

do with fuel flow and time is _ _ _ _ (analog, digital) in nature

all their forms, serve as the backbone of the Internet The Internet consists of academic, business, private, and government networks

The Internet allows users to access huge amounts of information using the World Wide Web (WWW) The Internet also supports two-way communications with e-mail and social

Internet Connection

Search the web for the following terms: fuel tank sending unit, vehicle speed sensor and engine control module

Trang 24

medi-of digital computers, huge memory banks, and the Internet

Millions of individual electronic devices must be designed, manufactured, tested, and repaired by technicians Electronics techni-cians and engineers are in great demand A few applications of digital electronics are sug-gested by the images on the tablet sketched in Fig 1-8

Desktop Tablets iPhone

Avionics Automation Cameras

TV-DVD Instrumentation Gaming

Security GPS Publishing

Internet e-mail Search Digital clock

Fig 1-8 Applications of digital electronics

Chapter 1 Digital Electronics

Jobs for technicians are available with most high-technology businesses Many govern-ment jobs call for some skills in computer technology including electronics Highly skilled technicians work on extremely sophis-ticated military electronics It is reported that the half the cost of some military aircraft is electronics in nature The military has many outstanding advanced electronics training programs Ask about these when you visit a military recruiter

The driving experience of a modern mobile has been greatly enhanced by electron-ics Automobile engines have more power, run smoother, and use less fuel due to precise elec-tronic engine control More automobiles con-tain entertainment systems that are outstanding Bluetooth for cell phones, GPS, and touch screen displays are common Assisted parking and blind spot detection are standard on many autos Safety features like antiskid and traction and stability control systems depend digital electronics Ask your school counselor about opportunities in your area

auto-To cut down on thefts, the key to your tomobile may contain a transmitter whose sig-nal is picked up by a transponder ECM The transponder reads the wireless signal from the key, allowing the engine to start Some mod-ern automobiles have more than 50 electronic control modules (computers) Auto mechan-ics must be trained in modern electricity and electronics Check with your area technical college to survey training openings Auto manufacturers also run outstanding training classes

au-Most measuring instruments you may use

at work in the lab will contain digital circuitry These might include a logic probe, digital multimeter (DMM), capacitance meter, frequency counter, function generator (signal generator), and programmable power supply Modern

oscilloscopes may also feature some digital circuitry

Many hands-on lab activities will be vided A updated Experiments Manual for Digital Electronics is available that pres-ents many hands-on lab activities chapter by chapter

Trang 25

pro-Answer the following questions

14 List at least four devices that use digital

Digital signals are composed of two

well-defined voltage levels Most of the voltage

levels used in this class will be about + 3 V to

+5 V for HIGH and near 0 V (GND) for LOW

These are commonly called TTL voltage

lev-els because they are used with the

transistor-transistor logic family of I Cs

Generating a Digital Signal

A TTL digital signal could be made manually

by using a mechanical switch Consider the

simple circuit shown in Fig l-9(a) As the blade

of the single-pole, double-throw (SPOT) switch

is moved up and down, it produces the digital

waveform shown at the right At time period t 1

the voltage is 0 V, or LOW At t2 the voltage is

+5 V, or HIGH At t 3 the voltage is again 0 V,

or LOW, and at t 4 it is again +5 V, or HIGH

The action of the switch causing the LOW,

HIGH, LOW, HIGH waveform in Fig 1-9(a)

is called toggling By definition, to toggle (the

verb) means to switch over to an opposite state

As an example in Fig 1-9(a), if the switch moves

from LOW to HIGH we say the output has

tog-gled Again if the switch moves from HIGH to

LOW we say the output has again toggled

One problem with a mechanical switch is

contact bounce If we could look very

care-fully at a switch toggling from LOW to HIGH,

it might look like the waveform in Fig 1-9(b)

The waveform first goes directly from LOW to

17 All auto mechanics that are specialists in electronics are self-taught (T or F)

18 List at least two measuring instruments you will use as a technician and that contain digital circuitry

HIGH (see point A) but then, because of tact bounce, drops to LOW (see point B) and then back to HIGH again Although this hap-pens in a very short time, digital circuits are fast enough to see this as a LOW, HIGH, LOW, HIGH waveform Note that Fig 1-9(b) shows that there is actually a range of voltages that are

con-defined HIGH and LOW The uncon-defined region

between HIGH and LOW may cause trouble in digital circuits and should be avoided

To cure the problem illustrated in Fig l-9(b),

mechanical switches are sometimes debounced

A block diagram of a debounced logic switch is

shown in Fig 1-9(c) Note the use of the ing circuit, or latch Some of the mechanical logic switches you will use on laboratory equipment will have been debounced with latch circuits

debounc-Latches are sometimes called flip-flops Notice

in Fig 1-9(c) that the output of the latch during time period t 1 is LOW but not quite 0 V During

t2 the output of the latch is HIGH even though it

is something less than a full +5 V Likewise t 3 is LOW and t

4 is HIGH in Fig 1-9(c)

It might be suggested that a push-button switch

be used to make a digital signal If the button

is pressed, a HIGH should be generated If the push button is released, a LOW should be gener-ated Consider the simple circuit in Fig 1-IO(a)

When the push button is pressed, a HIGH of about +5 V is generated at the output When the push button is released, however, the voltage at

the output is undefined There is an open circuit

between the power supply and the output This would not work properly as a logic switch

TTL voltage levels Transistor· transistor lagic

Debaunced lagic switch

Digital waveform Latch (flip-flap)

Contact bounce

Trang 26

_l Pressed= HIGH n -+-OUTPUT Released=?

One-shot multivibrator

connected to a one-shot multivibrator circuit

Now for each press of the push button, a single short, positive pulse is output from the one-shot circuit The pulse width of the output is deter-mined by the design of the multivibrator and

not by how long you hold down the push button

Multivibrator ·Circuits

Both the latch circuit and the one-shot circuit

were used earlier Both are classified as vibrator (MV) circuits The latch is also called

multi-a flip-flop or multi-a bistmulti-able multivibrmulti-ator The shot is also called the monostable multivibrator A third type of MV circuit is the astable multivibrator This is also called a free-running

one-multivibrator In many digital circuits it may be

referred to simply as the clock

The free-running MV oscillates by itself without the need for external switching or an external signal A block diagram of a free-run-ning MV is shown in Fig 1-11 The free-running

MV generates a continuous series of TTL level pulses The output in Fig 1-11 alternately tog-gles from LOW to HIGH, HIGH to LOW, etc

In the laboratory, you will need to ate digital signals The equipment you will use will have slide switches, push buttons, and free-running clocks that will generate TTL level sig-nals similar to those shown in Figs 1-9, 1-10, and

gener-1-11 In the laboratory, you will use logic switches

which will have been debounced using a latch

circuit as in Fig l-9(c) You will also use a pulse clock triggered by a push-button switch

single-10 Chapter 1 Digital Electronics

Trang 27

Free-running multivibrator

OITTPITT -+5V

-ov 5V-=-

-T

Fig 1-11 Free-running multivibrator generates a string of digital pulses

The single-pulse clock push button will be

con-nected to a one-shot multivibrator as shown in

Fig 1-lO(b) Finally, your equipment will have a

free-running clock It will generate a continuous

series of pulses, as shown in Fig 1-11

Wiring a Multivibrator

Astable, monostable, and bistable MVs can all be

wired using discrete components (individual

re-sistors, capacitors, and transistors) or purchased

in IC form Because of their superior

perfor-mance, ease of use, and low cost, the IC forms

of these circuits will be used in this course A

schematic diagram for a practical free-running

clock circuit is shown in Fig l-12(a) This clock

circuit produces a low-frequency (1- to 2-Hz)

TTL level output The heart of the free-running

clock circuit is a common 555 timer IC Note

that several resistors, a capacitor, and a power

supply must also be used in the circuit

A typical breadboard wiring of this

free-running clock is sketched in Fig l-12(b) Notice

the use of a solderless breadboard Also note that

pin 1 on the IC is immediately counterclockwise

from the notch or dot near the end of the

eight-pin IC The wiring diagram in Fig l-12(b) is

shown for your convenience You will normally

1 k!l 4 8

7 +

Wiring a Debounced Switch

Simple mechanical switches introduce problems when used as input devices to digital circuits The push-button switch (SW) shown in Fig 1-13(a)

is being pressed or closed at point A (see output waveform) Because of switch bounce the output signal goes HIGH, LOW, and then HIGH again

Likewise when the push-button switch is released (opened) at point B, more bouncing occurs Switch bounce from input switches must be eliminated

To solve the problem of switch bounce, a bouncing circuit has been added in Fig l-13(b)

de-Now when the push-button switch is closed at point C (see output waveform), no bouncing occurs and the output toggles from LOW to HIGH Likewise when SW1 is opened at point

D, no bouncing is observed on the waveform and the output toggles from HIGH to LOW

(see point E on waveform), the output toggles

from LOW to HIGH Later when SW1 is opened

OUTPUT

Fig 1-12(a) Schematic diagram of a Free-running clock using a 555 timer IC

Trang 28

Fig ·1-13 (a) Switch bounce caused by a mechanical switch (b) Debouncing circuit eliminates switch bounce

(see point Fon wave-form), the output of the 555 timer IC remains HIGH for a delay period After the delay period (about 1 second for this circuit) the output toggles from HIGH to LOW The delay pe-riod can be adjusted by changing the capacitance value of capacitor C2• Decreasing the capacitance

value of C2 will decrease the delay time at the put, while increasing c2 will increase the delay Wiring a One-Shot Multivibrator

out-A one-shot multivibrator (MV) is also called a

monostable multivibrator The one-shot circuit

Trang 29

-Switch debouncing circuit

-responds to an input trigger pulse with an

out-put pulse of a given width or time duration

A one-shot MV circuit that can be wired in

the lab is drawn in Fig 1-15 The 74121

one-shot multivibrator IC uses a simple push-button

switch to raise the voltage at input B from GND

to about + 3 V This is the trigger voltage When

triggered, the one-shot MV outputs a short pulse

at the two outputs The normal output Q (pin

6) emits a short positive pulse about 2 to 3 ms

+5V

INPUT

Vee

One-shot MV (74121) Q RExT/CExT

11

B Input

CEXT GND A1 A2 10

7 4 3

ns One-shot multivibrator circuit using the 74121 TTL IC

100 kn

OUTPUT Delay

The outputs of the 74121 one-shot multivibrator

IC come directly from an internal flip-flop and are therefore labeled Q and Q

Trang 30

Internet

Connection

Search the web

for LED, LCD, and

VFD seven-segment

displays

The pulse width generated by a one-shot

mul-ti vibrator is dependent on the design of the MV and not how long the input switch is pressed

The pulse width of the one-shot MV sketched

in Fig 1-15 can be increased by increasing the value of capacitor C1 and/or resistor R 3 De-creasing the values of capacitor C1 and resistor

R 3 will decrease the pulse width

As a practical matter, the input switch in Fig 1-15 may have to be debounced, or the multivibrator IC could emit more than a single pulse Using a good-quality "snap-action" push-button switch may also help avoid the problem

of false triggering by the one-shot MV circuit

Digital Trainer

A typical digital trainer used during lab sions is featured in Fig 1-16 The photograph actually shows a pair of PC boards specifi-cally designed to be used with this textbook's

ses-companion experiments manual Dynalogic's DT-1000 digital trainer board on the left in-cludes a solderless breadboard for hooking up circuits It also includes input devices such as

12 logic switches (two are debounced), a pad, a one-shot MV, and a variable frequency clock (astable MV) Output devices mounted

key-on the DT-1000 trainer board include 16 LED output indicators, a piezo buzzer, a relay, and a small de motor Power connections are available

on the upper left of the DT-1000 digital trainer board On the right in Fig 1-16 is a second PC board which contains sophisticated LED, LCD, and VFD displays Dynalogic's DB-1000 dis-play board is very useful when seven-segment displays are used as outputs These boards along with individual ICs and other components could

be used during your lab sessions to enable you to gain practical experience in digital electronics

Fig 1-'16 Digital trainer and display boards used to set up lab experiments

Supply the missing word in each statement

19 Refer to Fig l-9(c) The digital signal at

Trang 31

22 Refer to Fig 1-lO(b) The one-shot

multi-vibrator used for generating the digital

signal is also called a(n) _ _ _ _

multi vibrator

23 Refer to Fig 1-12 A 555 IC

and several discrete components are being

used to generate a continuous series of

TTL level pulses This free-running clock

is also called a free-running multivibrator

24 Refer to Fig 1-14 The 555 timer IC is

being used along with several discrete

increase the voltage of) push-button

switch SW1•

25 Refer to Fig 1-15 The 74121 IC is being

one-shot) multivibrator

26 Refer to Fig 1-15 The 74121 IC has two

outputs (labeled Q and Q) generating

_ _ _ _ (complementary, in-phase)

output pulses

1-5 How Do You Test for a

Digital Signal?

In the last section you generated digital signals

using various MV circuits These are the

meth-ods you will use in the laboratory to generate

input signals for the digital circuits constructed

In this section, several simple methods of testing

the outputs of digital circuits will be discussed

Consider the circuit in Fig l-17(a) The input

is provided by a simple SPOT switch and power

28 Refer to Fig 1-16 The one shot at the left

on the DT-1000 board emits a single pulse each time the push-button switch is pressed

The one shot is also called a(n) _ _ _ _ (astable, monostable) multivibrator

29 Refer to Fig 1-16 The clock at the left on the DT-1000 board generates a string of digital pulses The clock is also called a(n) (astable, bistable) multi vibrator

30 Refer to Fig 1-16 The DT-1000 digital trainer board on the left features several output devices List at least three of these output devices

31 RefertoFig.1-16 TheDB-lOOOdisplay board on the right features what three types of seven-segment displays?

supply The output indicator is an LED

(light-emitting diode) The 150-D resistor limits the current through the LED to a safe level When the switch in Fig l-17(a) is in the HIGH (up) position, +5 V is applied to the anode end of the LED The LED is forward-biased, current flows upward, and the LED lights With the switch in the LOW (down) position, both the anode and cathode ends of the LED are grounded, and it does not light Using this indicator, a light means HIGH and no light generally means LOW

INPUT Logic switch

Trang 32

Another LED output indicator is illustrated

in Fig 1-18 The LED acts exactly the same as the one shown previously It lights to indicate

a logical HIGH and does not light to indicate

a LOW The LED in Fig 1-18 is driven by an NPN transistor instead of directly by the input

+5V

~1500

A

OUTPUT Light= HIGH

~No light= LOW

Fig 1-18 Transistor-driven LED output indicator

390 fl

y

OUTPUT +

;/

Fig 1-'!9 LED output indicators that will show LOW, HIGH, and undefined logic levels

The transistorized circuit in Fig 1-18 holds an advantage over the direct-drive circuit in that

it draws less current from the switch or an put of the digital circuit under test Light-emit-ting diode output indicators wired like the one shown in Fig 1-18 may be found in your labora-tory equipment

out-Consider the output indicator circuit using two LEDs shown in Fig 1-19 When the input

is HIGH ( +5 V), the bottom LED lights while the top LED does not light When the input is LOW (GND), only the top LED lights If point

Yin the circuit in Fig 1-19 enters the undefined

region between HIGH and LOW or is not nected to a point in the circuit, both LEDs light Output voltages from a digital circuit can be measured with a standard voltmeter With the TTL family of ICs, a voltage from 0 to 0.8 V

con-is considered a LOW A voltage from 2 to 5 V

is considered a HIGH Voltages between about 0.8 and 2 V are in the undefined region and sig-nal trouble in TTL circuits

Logic levels are shown in graphic form

in Fig 1-20 It should be noted that a typical operating voltage for transistor-transistor logic (TTL) circuits is +5 V Depending on the sub-family of complementary metal-oxide semi-conductor (CMOS) digital circuits, they may operate on a wide range of operating voltages including +12 V, +9 V, +5 V, or even less The definition of what TTL and CMOS circuits con-sider HIGH and LOW is different Notice that the range of voltages between HIGH and LOW

in both TTL and CMOS is called the undefined region Voltages in the undefined region cause trouble in digital circuits

GND voltage

l2!J Defining logic levels for the TTL and CMOS families

of digital ICs

Trang 33

A handy portable measuring instrument

used to determine logic level is the logic probe

A simple version of the logic probe is sketched

in Fig 1-21(a) Before testing a circuit, this

logic probe requires the operator to select the

type of digital circuitry being tested Move the

selector switch to either TTL or CMOS TTL

and CMOS are two different families of digital

circuits The graph in Fig 1-20 suggested the

definitions of HIGH, LOW, and undefined are

different

GND

TTL

Power to operate the logic probe is provided

by the digital circuit you are testing The two leads coming out the end of the logic probe are connected to the + V (red lead) and negative GND (black lead) The pointed metal tip of the logic probe is touched to the point in the circuit you are testing The appropriate output LED on the logic probe will light (HIGH or LOW), de-pending on the logic level at the input metal tip

A TTL digital circuit is being tested with a simple logic probe in Fig l-21(b) Switch logic

(a)

OUTPUTS (TTL)

Logic probe

Trang 34

probe to TTL (not CMOS) The red and black leads are connected to the voltages that operate the circuit Next turn the power on Five logic probe tests are performed as follows:

Test #1: Touch tip to + 5-V input

Result: Reads HIGH logic level

This is correct

Test #2: Touch tip to GND input

Result: Reads LOW logic level

This is correct

Test#3: Touch tip to outputA

Result: Reads LOW logic level

This is correct

Test #4: Touch tip to output B

Result: Reads HIGH logic level

This is correct

Test #5: Touch tip to output C

Result: No reading on HIGH or LOW

indicators

Supply the missing word or words in each statement

32 RefertoFig.1-17.IftheinputisHIGH,

light) because the diode is _ _ _ _ (forward-, reverse-) biased

33 Refer to Fig 1-18 If the input is LOW, the transistor is turned (off,

not) light

34 Refer to Fig 1-19 If the input is HIGH,

has +5 V applied, forward-biasing the diode

35 Refer to Fig 1-20 and assume a 5-V power supply In a TTL circuit, a volt-age of 2.5 V would be considered a(n) _ _ _ _ (HIGH, LOW, undefined) logic level

This means that the output is neither HIGH nor LOW but floating in the undefined region or is open This is a problem that must be repaired!

A floating output from a digital circuit was detected in test #5 in Fig l-2l(b) Floating in-puts or outputs commonly mean a fault in the circuit and must be repaired

Testing with a logic probe as in Fig l-2l(b) can be one of the steps in troubleshooting Knowledge of circuit operation is the key to effective troubleshooting

You will notice that we are testing a TTL ital circuit that has static outputs Logic probes are good for this type of testing but not suited for

dig-circuits that have constantly changing outputs

In the laboratory, you will use a logic probe

to test and troubleshoot your breadboarded tal circuits The operating instructions are dif-ferent for each model of logic probe Read the instruction manual on the unit you will be using

digi-36 Refer to Fig 1-20 and assume a+ 12-V power supply In a CMOS circuit, a volt-age of 2 V would be considered a(n) _ _ _ _ (HIGH, LOW, undefined) logic level

37 Refer to Fig 1-21(a) This logic probe is powered by _ _ _ _

a A solar cell

b A 9-V battery

c Power from the circuit being tested

38 Refer to Fig 1-2l(b) Test #5 indicates an open or output C of the digital circuit is floating in the undefined region for TTL circuits (Tor F)

39 Refer to Fig l-21(b) The finding tected in test #5 will not cause problems because the unit is a TTL digital circuit (Tor F)

Trang 35

Fig 1-22 Function generator

1-6 Simple Instruments

Several basic commercial instruments used

with digital circuits are introduced in this

sec-tion Simplified generic instruments are

fea-tured Real commercial function generators,

logic probes, and oscilloscopes have more

ad-vanced features

Function Generator

One useful output device available in most

school and industrial labs is the function

gen-erator A simple function generator is sketched

in Fig 1-22 If you work with a digital trainer

(DT-1000 trainer in Fig 1-16) in your school

lab, it may contain outputs like those of a

func-tion generator

To use the function generator, you first

se-lect the shape of the waveform A square wave

would be selected when working with most

digital circuits Second, the frequency (in hertz,

or Hz) may be selected using the range switch

along with the variable multiplier dial Third,

the output voltage is selected This function

gen-erator features two separate voltage outputs (5-V

TTL and variable) The 5-V TTL output is handy

for driving many TTL logic circuits If you use

the variable output on the function generator, the

amplitude knob will adjust the output voltage

What is the shape and frequency of the

waveform being generated by the function

generator pictured in Fig 1-22? The shape

knob is in the square-wave position The range

0

5-VTIL

frequency selector knob points at 10 Hz The multiplier frequency dial points at 1 The out-put frequency is 10 Hz (range X multiplier = frequency or 10 X 1 = 10 Hz) In Fig 1-22, the output is taken from the 5-V TTL output of the instrument This output will directly drive a TTL logic circuit

logic Probe The most basic instrument for testing the digital logic levels is the logic probe A sim-ple logic probe is sketched in Fig 1-23 The slide switch is used to select the type of logic family under test, either TTL or CMOS The logic probe pictured in Fig 1-23 is set to test

a TTL-type digital circuit Typically, two leads provide power to the logic probe The red lead is connected to the positive ( +) of the

Fig 1-23 Logic probe

Trang 36

power supply and the black lead is connected

to negative (-) or GND of the power supply

After powering the logic probe, the needlelike probe is touched to the test point in the circuit

Either the HIGH (red LED) or LOW (green LED) indicator will light If neither or both indicators light, it usually means the voltage

is somewhere between HIGH and LOW defined region) As a reminder, definitions for

(un-HIGH, LOW, and undefined logic levels are detailed in Fig 1-20

The logic probe will be a useful tool when you wire and test digital circuits in the school lab Read the operating instructions for your specific logic probe

Oscilloscope The oscilloscope is a very versatile piece of test equipment A simplified generic oscilloscope,

or "scope," is sketched in Fig 1-24 The basic function of the oscilloscope is to graph time versus input voltage Time is the horizontal

DC input

distance on the screen and voltage is the cal deflection Oscilloscopes work best on sig-nals that repeat over and over

verti-Consider the digital signal of 4 V p-p, 100 Hz shown entering the scope's input in Fig 1-24 The horizontal sweep time knob on the scope has been set to 2 ms (2 milliseconds = 0.002 second) This will cause a dot of light to move across the screen from left to right at 2 ms per division (20 ms to cross the entire screen) The dot of light will then jump back to the left end of the screen to start the process again The

vertical deflection knob on the scope is set at

1 V per division

In this example, a signal voltage of 0 V, to +4 V is entering the input Starting at the left edge of the scope face, first, the dot is deflected four divisions (1 V per division) upward for the

first S ms Second, the input voltage drops to

0 V, and the lighted dot traces the bottom line

for S ms Third, the input voltage jumps to +4 V

with the second upper trace Fourth, the voltage

HORIZONTAL SWEEP TIME

Trang 37

drops to 0 V with the second lower trace Finally,

the lighted dot jumps back to the left of the screen

and then repeats TTL logic levels are labeled on

Fig 1-24 as HIGH (+4 V) and LOW (0 V)

Consider the wave traced on the

oscillo-scope's screen in Fig 1-24 The shape of the

signal is a square wave Square waves are

use-ful in digital electronics A careuse-ful look will

show that two waveforms are displayed on the

screen We say that two cycles are displayed

Look at the waveform on the scope in Fig 1-24

What is the time duration for one cycle? You will

count five divisions This means that the time

duration of the first cycle is 10 ms (5 divisions X

Supply the answers for each question

40 List two instruments used to detect and

measure digital signals

41 A (function generator, logic

analyzer) is a laboratory instrument that

can generate electronic signals This

DC input

POWER= ON

Fig 1-25 Oscilloscope problem

2 ms/division = 10 ms) From the time duration

of 10 ms (O.DlO second), you can calculate the frequency of the input voltage using the for-

mula f = lit, where f is the frequency in Hz (cycles per second) and tis the time in seconds

Calculating the frequency of the input signal

in Fig 1-24 yields a frequency of 100 Hz (f = 1/0.01 s) Notice that the oscilloscope has aided

us in determining the shape and frequency of

the input waveform

Oscilloscopes you will use in the lab will be more complicated than the simplified version shown in Fig 1-24 However, the basic function

of the scope has been illustrated

instrument has controls available for varying the voltage, shape, and frequency

of the output signal

42 Refer to Fig 1-25 How many cycles are displayed on the screen of the oscilloscope?

HORIZONTAL SWEEP TIME

INPUT

Input signal

Calculate frequency

Trang 38

43 Refer to Fig 1-25 What is the time tion for one cycle?

dura-44 Refer to Fig 1-25 What is the frequency

of the input signal?

45 Refer to Fig 1-25 What is the peak (p-p) voltage of the input signal?

peak-to-22 Chapter 1 Digital Electronics

46 Refer to Fig 1-25 The digital input

10 ms) and goes LOW for _ _ _ _ (4 ms, 8 ms)

Trang 39

l Summary and Review

1 Analog signals vary gradually and continuously,

while digital signals produce discrete voltage

levels commonly referred to as HIGH and LOW

2 Most modem electronic equipment contains both

analog and digital circuitry

3 Logic levels are different for various digital logic

families, such as TTL and CMOS These logic

levels are commonly referred to as HIGH, LOW,

and undefined Figure 1-20 details these TTL and

CMOS logic levels

4 Digital circuits have become very popular because

of the availability of low-cost digital ICs Other

advantages of digital circuitry are computer

compatibility, memory, ease of use, simplicity of

design, accuracy, and stability

5 Modern automobiles are examples of the extensive

use of both analog sensors interfaced with dozens

of digital engine control modules (ECMs) These

ECMs make thousands of decisions a second,

controlling the overall driving quality and safety of

the modem automobile

Answer the following questions

1-1 Define the following:

a Analog signal

b Digital signal

1-2 Draw a square-wave digital signal Label the

bottom "O V" and the top "+ 5 V." Label the

HIGH and LOW on the waveform Label the

logical 1 and logical 0 on the waveform

1-3 List two devices that contain digital circuits

which do mathematical calculations

1-4 Refer to Fig 1-6 The processing, storage of

data, and output in this system consist mostly of

_ _ _ _ (analog, digital) circuits

1-5 Refer to Fig l-7(a) The gradually varying

cur-rent sent from the fuel tank sending unit to the fuel

6 Digital electronics is a huge and rapidly expanding field Digital computers, in all their forms, serve as the backbone of the Internet

7 Bistable, monostable, and astable multi vibrators are used to generate digital signals These are sometimes called latches, one-shot, and free-running multivibrators, respectively

8 Logic level indicators may take the form of simple LED and resistor circuits, voltmeters, or logic probes Light-emitting diode logic level indicators will probably be found on your laboratory equipment

9 A function generator is a lab instrument used

to generate electronic signals The operator can vary an output signal's voltage, frequency, and shape

10 An oscilloscope is a widely used test and troubleshooting instrument used to graph signals Oscilloscopes are useful in showing waveform shape, time duration, and frequency of repetitive signals

gauge on this older auto instrument panel is fied as a(n) (analog, digital) signal 1-6 Refer to Fig l-7(b) The modem automobile in-strument panel module is a digital computerlike unit that can drive the fuel gauge and calculate and display fuel consumption as average miles per gallon and miles till empty List the sensors and modules that must input data into the in-strument panel module

classi-1-7 Traditionally, most consumer electronic devices (TVs, radios, and phones) have used _ _ _ _ (analog, digital) circuitry

1-8 Unwanted electrical interference in electronic circuitry is commonly called _ _ _ _ (gobo, noise)

Trang 40

1-9 An electronic product that has an alphanumeric

display, is programmable, and can store

digital) circuitry

1-10 Digital circuitry is becoming more pervasive

because information storage is easy, the device

less) accuracy and precision are possible

1-11 List two electronic devices you personally use

that contain digital circuitry

1-12 The military has excellent electronics training

schools (Tor F)

1-13 List two pieces oflab equipment you will use

that contains digital circuitry

1-14 Refer to Fig 1-9 When using a SPDT switch to

produce a digital signal, a(n) latch is

used to condition the output

1-15 Refer to Fig 1-10 A(n) _ _ _ _ _ _ _ _

multivibrator is commonly used to condition the

output of a push-button switch when generating

a single digital pulse

multi-vibrator produces a string of digital pulses

1-17 The circuit in Fig 1-12 is classed as a(n)

_ _ _ _ (astable, bistable) multivibrator

1-18 Refer to Fig 1-16 The one-shot MV on the

of pulses, single pulse) when the push button is

pressed once

1-19 Refer to Fig 1-16 The clock on the DT-1000

of pulses, single pulse) and the circuit can be

referred to as a(n) (astable,

mono-stable) multivibrator

1-20 Refer to Fig 1-16 The two solid-state logic

switches on the DT-1000 trainer are _ _ _ _

(analog, debounced)

1-21 Refer to Fig 1-16 The DB-1000 board

features what three types of seven-segment

displays?

1-22 The LED in Fig 1-17(b) lights when the input

1-23 Refer to Fig 1-19 The (bottom, top)

LED lights when the input switch is LOW

1-24 Refer to Fig 1-20 and assume a 5-V power

supply In a TTL circuit, a voltage of 1.2 V

LOW, undefined) logic level

1-25 Refer to Fig 1-20 and assume a 10-V power supply In a CMOS circuit, a voltage of 9 V

1-26 Refer to Fig 1-20 and assume a 10-V power supply In a CMOS circuit, a voltage of 0.5 V

1-27 When referring to digital ICs, TTL stands for

1-28 When referring to digital ICs, CMOS stands for

1-29 Refer to Fig 1-14 The 555 timer IC is wired to function as a(n) (astable MV, switch debouncing) circuit

1-30 Refer to Fig 1-14 Increasing the capacitance value of c2 will (decrease, increase) the time delay of the output waveform

1-31 Refer to Fig 1-15 The 74121 IC can be scribed as a(n) (astable, bistable, monostable) multivibrator

de-1-32 Refer to Fig 1-15 Activating input switch

SW1 causes a short (negative pulse, positive pulse) to be emitted from the normal

Q output of the 7 4121 one-shot multi vibrator

IC

1-33 A flip-flop is the name for a device classified

monos-table) multivibrator

1-34 The repeated action of a switch or other device causing a LOW, HIGH, LOW, HIGH output is

1-35 Refer to Fig 1-22 The output from the function generator is a 5-V TTL square-wave signal that

1-36 Refer to Fig 1-23 This logic probe can test

circuits

1-3 7 The advantage of the oscilloscope in testing and troubleshooting is that voltage, time dura-

level, shape) of a waveform can be easily determined

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