Lesson 20 Flip-Flop电子技术专业英语教程

Lesson20Flip-Flop《电子技术专业英语教程》冯新宇主编电子工业出版社www.phei.com.cnUnit7DigitalLogicCircuit2019/8/3《电子技术专业英语教程》2Lesson20Flip-Flop•Backgrounds•Texttour•Languageinuse–Vocabulary–Structure–Reading/writingtechniques2019/8/3《电子技术专业英语教程》3•Terminology–multivibrator•n.【计】多谐振荡器–fieldeffecttransistor•【计】场效应晶体管–shiftregister•移位寄存器Backgrounds2019/8/3《电子技术专业英语教程》4Texttour•Outline–Flip-flop–Flip-flop’sinvention–Simpleflip-flops–Clockedflip-flops–Thetypeofflip-flops•Set–resetflip-flops(SRflip-flops)•Triggerflip-flops(Tflip-flops)•JKflip-flop•Dflip-flop2019/8/3《电子技术专业英语教程》5Flip-flop•Indigitalcircuits,aflip-flopisatermreferringtoanelectroniccircuit(abistablemultivibrator)thathastwostablestatesandtherebyiscapableofservingasonebitofmemory.•Today,thetermflip-flophascometomostlydenotenon-transparent(clockedoredge-triggered)devices,whilethesimplertransparentonesareoftenreferredtoaslatches;however,asthisdistinctionisquitenew,thetwowordsaresometimesusedinterchangeably.•Aflip-flopisusuallycontrolledbyoneortwocontrolsignalsand/oragateorclocksignal.Theoutputoftenincludesthecomplementaswellasthenormaloutput.Asflip-flopsareimplementedelectronically,theyrequirepowerandgroundconnections.2019/8/3《电子技术专业英语教程》6Flip-flop’sinvention•Thefirstelectronicflip-flopwasinventedin1918byWilliamEcclesandF.W.Jordan.•ItwasinitiallycalledtheEccles-Jordantriggercircuitandconsistedoftwoactiveelements.•Thenameflip-flopwaslaterderivedfromthesoundproducedonaspeakerconnectedtooneofthebackcoupledamplifiersoutputsduringthetriggerprocesswithinthecircuit.•Thisoriginalelectronicflip-flop——asimpletwo-inputbistablecircuitwithoutanydedicatedclocksignalwastransparent,andthusadevicethatwouldbelabeledasalatchinmanycirclestoday.2019/8/3《电子技术专业英语教程》7Simpleflip-flops•Simpleflip-flopscanbebuiltaroundapairofcross-coupledinvertingelements:vacuumtubes,bipolartransistors,fieldeffecttransistors,inverters,andinvertinglogicgateshaveallbeenusedinpracticalcircuits-perhapsaugmentedbysomegatingmechanism.•Themoreadvancedclockeddevicesarespeciallydesignedforsynchronoussystems;suchdevicesthereforeignoreitsinputsexceptatthetransitionofadedicatedclocksignal.•Thiscausestheflip-floptoeitherchangeorretainitsoutputsignalbaseduponthevaluesoftheinputsignalsatthetransition.•Someflip-flopschangeoutputontherisingedgeoftheclock,othersonthefallingedge.2019/8/3《电子技术专业英语教程》8Clockedflip-flops•Clockedflip-flopsaretypicallyimplementedasmaster-slavedeviceswheretwobasicflip-flops(plussomeadditionallogic)collaboratetomakeitinsensitivetospikesandnoisebetweentheshortclocktransitions;theyneverthelessalsooftenincludeasynchronousclearorsetinputswhichmaybeusedtochangethecurrentoutputindependentoftheclock.2019/8/3《电子技术专业英语教程》9Thetypeofflip-flops•Flip-flopscanbefurtherdividedintotypesthathavefoundcommonapplicabilityinbothasynchronousandclockedsequentialsystems:theSR(set-reset),D(dataordelay),T(trigger),andJKtypesarethecommonones;allofwhichmaybesynthesizedfromothertypesbyafewlogicgates.•Thebehaviorofaparticulartypecanbedescribedbywhatistermedthecharacteristicequation,whichderivesthenext(i.e.,afterthenextclockpulse)output,Qnext,intermsoftheinputsignal(s)and/orthecurrentoutput,Q.2019/8/3《电子技术专业英语教程》10Set–resetflip-flops(SRflip-flops)•ThefundamentallatchisthesimpleSRflip-flop,whereSandRstandforsetandresetrespectively.•Itcanbeconstructedfromapairofcross-coupledNANDorNORlogicgates.ThestoredbitispresentontheoutputmarkedQ.SRFlip-FlopoperationCharacteristictableExcitationtableSRActionQ(t)Q(t+1)SRAction00Keepstate000xNochange01Q=00110Set10Q=11001Reset11Unstablecombination11x0Nochange2019/8/3《电子技术专业英语教程》11Set–resetflip-flops(SRflip-flops)•Normally,instoragemode,theSandRinputsarebothlow,andfeedbackmaintainstheQandoutputsinaconstantstate,withthecomplementofQ.•IfSispulsedhighwhileRisheldlow,thentheQoutputisforcedhigh,andstayshighevenafterSreturnslow;similarly,ifRispulsedhighwhileSisheldlow,thentheQoutputisforcedlow,andstayslowevenafterRreturnslow.•Figure20-1showsthesymbolforaSRlatch.Figure20-1ThesymbolforaSRlatch2019/8/3《电子技术专业英语教程》12Triggerflip-flops(Tflip-flops)•IftheTinputishigh,theTflip-flopchangesstate(toggles)whenevertheclockinputisstrobed.IftheTinputislow,theflip-flopholdsthepreviousvalue.Thisbehaviorisdescribedbythecharacteristicequation:•(or,withoutbenefitoftheXORoperator,theequivalent:)•andcanbedescribedinatruthtable:QTQnextQTQnextQTQTQnextTFlip-FlopoperationCharacteristictableExcitationtableTQQnextCommentQQnextTComment000holdstate000Nochange011holdstate110Nochange101toggle011Complement110toggle101Complement2019/8/3《电子技术专业英语教程》13Triggerflip-flops(Tflip-flops)•Figure20-2showsT-typeflip-flop.•WhenTisheldhigh,thetriggerflip-flopdividestheclockfrequencybytwo;thatis,ifclockfrequencyis4MHz,theoutputfrequencyobtainedfromtheflip-flopwillbe2MHz.•This'divideby'featurehasapplicationinvarioustypesofdigitalcounters.•ATflip-flopcanalsobebuiltusingaJKflip-flop(J&KpinsareconnectedtogetherandactasT)orDflip-flop(TinputandQpreviousisconnectedtotheDinputthroughanXORgate).Figure20-2T-typeflip-flop2019/8/3《电子技术专业英语教程》14JKflip-flop•TheJKflip-flopaug