数字电子技术(课件)lec17.ppt

2020 1 24 Chapter8Counters 1 Chapter8Outline 8 1AsynchronousCounterOperation8 2SynchronousCounterOperation8 3Up DownSynchronousCounters8 4DesignofSynchronousCounters Mealytypesequentiallogicdesign8 5CascadedCounters8 6CounterDecoding8 7CounterApplications8 8LogicSymbolswithDependencyNotation DigitalSystemApplications TrafficLight Lecture17 Asynch SynchCounters Lecture17 Lecture18 Lecture19 Lecture20 2020 1 24 Chapter8Counters 2 KeyKnowledgeinLecture16 Lecture17 Asynch SynchCounters Operationprincipleofasynchronousandsynchronousbinarycounters Operationprincipleofasynchronousandsynchronousdecadecounters Developcountertimingdiagrams Counterauto reentryproperty UsageofsomeMSIcounters DifficultTopics Timingdiagrams Counterauto reentryproperty 2020 1 24 Chapter8Counters 3 AsynchronousCounterOperation Anasynchronouscounterisoneinwhichtheflip flops FF withinthecounterdonotchangestatesatexactlythesametimebecausetheydonothaveacommonclockpulse Lecture17 Asynch SynchCounters A2 bitAsynchronousBinaryCounter withJ K 1 toggleconnection 2020 1 24 Chapter8Counters 4 TimingDiagramforThe2 BitCounter Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 5 BinaryStateSequenceforTheCounter Lecture17 Asynch SynchCounters OpenfileF08 01toverifyoperation 2020 1 24 Chapter8Counters 6 3 BitAsynchronousBinaryCounter Lecture17 Asynch SynchCounters Statesequencefora3 bitbinarycounter 2020 1 24 Chapter8Counters 7 LogicCircuitandTimingDiagramforonecycle Lecture17 Asynch SynchCounters OpenfileF08 03toverifyoperation 2020 1 24 Chapter8Counters 8 IllustrationofPropagationDelays Lecture17 Asynch SynchCounters Seedemo 2020 1 24 Chapter8Counters 9 IllustrationExample Lecture17 Asynch SynchCounters Givenabinarycounterbelow developatimingdiagramforQ0 Q3 determinethetotalpropagationdelayifeachFFhasa10nsdelay Alsodeterminethemaximumclockfrequency 2020 1 24 Chapter8Counters 10 SolutiontotheExample Lecture17 Asynch SynchCounters Thetimingdiagramisshownbelow Totaldelaytp tot 4x10ns 40ns Themaximumclockfrequencyis 2020 1 24 Chapter8Counters 11 AsynchronousDecadeCounters Lecture17 Asynch SynchCounters Themodulusofacounteristhenumberofuniquestatesthroughwhichthecounterwillsequence Themaximummodulusofacounteris2n wherenisthenumberofflip flopsinthecounter Counterscanbedesignedtohaveanumberofstatesintheirsequencethatislessthanthemaximumof2n thistypeofsequenceiscalledatruncatedsequence Onecommonmodulusforcounterswithtruncatedsequenceisten calledMOD10 Counterswithtenstatesintheirsequencearecalleddecadecounters Toobtainatruncatedsequence itisnecessarytoforcethecountertorecyclebeforegoingthroughallofitspossiblestates 2020 1 24 Chapter8Counters 12 AnAsynchDecadeCounterUsingPartialDecoding Lecture17 Asynch SynchCounters Seedemofig8 6 ms9 2020 1 24 Chapter8Counters 13 TestYourUnderstanding Lecture17 Asynch SynchCounters Howtoimplementanasynchronouscounterhavingamodulusoftwelvewithastraightbinarysequencefrom0000through1011 Howmanyflip flopsarerequired 4 Codeusedforpartialdecoding 1100 2020 1 24 Chapter8Counters 14 TimingDiagramofModulusTwelveCounter Lecture17 Asynch SynchCounters Wheredotheglitchesoccur 2020 1 24 Chapter8Counters 15 异步十进制计数器的另一种电路结构 有些数字电路对毛刺很敏感 引起误动作必须消除 二进制计数器计数到10时 对计数器清零的方式有多种 请看右边的电路 当计数器计数到1001时 Q1Q2正好为0 将它们相与后作为FF3的J输入 且第十个时钟到来时 Q0将正好变成0 请看时序图 演示 Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 16 The74LS934 BitAsynchronousBinaryCounter Lecture17 Asynch SynchCounters ItcanalsobeusedasaMOD16CTR Seedemo 2020 1 24 Chapter8Counters 17 TwoConfigurationsofthe74LS93AsynchCounter Lecture17 Asynch SynchCounters Thequalifyinglabel CTRDIVn indicatesacounterwithnstates Howtoconnect74LS93asamodulus 12counter 2020 1 24 Chapter8Counters 18 74LS93ConnectedAsaModulus 12Counter Lecture17 Asynch SynchCounters Seedemo 2020 1 24 Chapter8Counters 19 二 五 十进制异步计数器74LS290 使用方法 1 以CLK0为计数输入端 Q0为输出端 即得到二进制计数器 3 将CLK1与Q0相连 同时以CLK0为计数输入端 Q3Q2Q1Q0为输出端 则得到十进制计数器 这就是为什么这个电路被称为二 五 十进制异步计数器的原因 见仿真演示 Lecture17 Asynch SynchCounters 2 以CLK1为计数输入端 Q3Q2Q1为输出端 即得到五进制计数器 2020 1 24 Chapter8Counters 20 SynchronousCounterOperation Lecture17 Asynch SynchCounters Asynchronouscounterisoneinwhichalltheflip flopsinthecounterareclockedatthesametimebyacommonclockpulse A2 BitSynchronousBinaryCounter ToggleswhenQ0 1 IfQ0 0Nochange 2020 1 24 Chapter8Counters 21 TimingDiagramforTheExampleCounter Lecture17 Asynch SynchCounters Flip flopchangesstateattherisingedgeoftheclockbasedonthestateequation InitialQ0 0 Q1 0 2020 1 24 Chapter8Counters 22 A3 BitSynchronousBinaryCounter Lecture17 Asynch SynchCounters J0 K0 1 J1 K1 Q0 J2 K2 Q0Q1 2020 1 24 Chapter8Counters 23 TimingDiagramforThe3 BitCounter Lecture17 Asynch SynchCounters OpenfileF08 14toverifytheoperation 2020 1 24 Chapter8Counters 24 A4 BitSynchBinaryCounterandTimingDiagram Lecture17 Asynch SynchCounters Generallyspeaking 2020 1 24 Chapter8Counters 25 A4 BitSynchronousBCD Decade Counter Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 26 Q3Q2Q1Q0 Q3Q2Q1Q0 BCDDecadeCounterTransitionTable Lecture17 Asynch SynchCounters Calculationillustration No 2020 1 24 Chapter8Counters 27 TimingDiagramforTheBCDDecadeCounter Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 28 Auto ReentryPropertyAnalysis Supposeforsomereason maybenoise thecounterisoffthenormaltenstates andenteredoneofthesixinvalidstates canthecounterreenterthenormalstatesautomatically Lecture17 Asynch SynchCounters 6isavalidstate auto reentryOK 2020 1 24 Chapter8Counters 29 Q3Q2Q1Q0 Validstates BCDDecadeCounterTransitionDiagram Lecture17 Asynch SynchCounters Seedemofig8 17 2020 1 24 Chapter8Counters 30 The74HC1634 BitSynchronousBinaryCounter Lecture17 Asynch SynchCounters isusedtoresetcounter Enableactive HIGH usedincascadeforhighercountsequence 注意 ENT 1 ENP 0停止计数但进位保持 2020 1 24 Chapter8Counters 31 TimingExamplefora74HC163 Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 32 74161四位同步二进制计数器 Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 33 The74F160SynchronousBCDDecadeCounter Lecture17 Asynch SynchCounters isusedtoresetcounter Enableactive HIGH usedincascadeforhighercountsequence 2020 1 24 Chapter8Counters 34 TimingExamplefora74F160 Lecture17 Asynch SynchCounters 2020 1 24 Chapter8Counters 35 TestYourUnderstanding Lecture17 Asynch SynchCounters Amodulus 12countermusthavea 12flip flops b 3flip flopsc 4flip flops d synchronousclocking Answer c 2 Whichoneofthefollowingisanexampleofacounterwithatruncatedmodulus a Modulus8 b Modulus14c Modulus16 d Modulus32 Answer b 2020 1 24 Chapter8Counters 36 TestYourUnderstanding Lecture17 Asynch SynchCounters 3 A4 bitripplecounterconsistsofflip flopsthateachhaveapropagationdelayfromclocktoQoutputof12ns Forthecountertorecyclefrom1111to0000 ittakesatotalofa 12ns b 24ns c 48ns d 36ns Answer c 4 Theterminalcountofamodulus 13binarycounterisa 0000 b 1111 c 1101 d 1100 Answer d 2020 1 24 Chapter8Counters 37 Lecture17 Asynch SynchCounters TestYourUnderstanding Whatisthecountingsequenceandmodulusforthefollowingcounter Answer countingsequence 0 1 2 3 4 5 9 0 Modulus 7 2020 1 24 Chapter8Counters 38 SummaryofLecture17 Lecture17 Asynch SynchCounters Acounterwithmodu