Digital Circuits - Flip-Flops - Tutorialspoint

D flip-flop operates with only positive clock transitions or negative clock transitions. Whereas, D latch operates with enable signal. That means, the output of ... Home CodingGround Jobs Whiteboard Tools Business Teachwithus DigitalCircuitsTutorial Home NumberSystems BaseConversions BinaryNumbersRepresentation SignedBinaryArithmetic Codes ErrorDetection&CorrectionCodes BooleanAlgebra CanonicalandStandardForms K-MapMethod Quine-McCluskeyTabularMethod LogicGates Two-LevelLogicRealization CombinationalCircuits ArithmeticCircuits Decoders Encoders Multiplexers De-Multiplexers ProgrammableLogicDevices ThresholdLogic SequentialCircuits Latches Flip-Flops ConversionofFlip-Flops ShiftRegisters ApplicationofShiftRegisters Counters FiniteStateMachines AlgorithmicStateMachineCharts DigitalCircuitsResources DigitalCircuits-QuickGuide DigitalCircuits-UsefulResources DigitalCircuits-Discussion SelectedReading UPSCIASExamsNotes Developer'sBestPractices QuestionsandAnswers EffectiveResumeWriting HRInterviewQuestions ComputerGlossary WhoisWho DigitalCircuits-Flip-Flops Advertisements PreviousPage NextPage  Inpreviouschapter,wediscussedaboutLatches.Thosearethebasicbuildingblocksofflip-flops.Wecanimplementflip-flopsintwomethods. Infirstmethod,cascadetwolatchesinsuchawaythatthefirstlatchisenabledforeverypositiveclockpulseandsecondlatchisenabledforeverynegativeclockpulse.Sothatthecombinationofthesetwolatchesbecomeaflip-flop. Insecondmethod,wecandirectlyimplementtheflip-flop,whichisedgesensitive.Inthischapter,letusdiscussthefollowingflip-flopsusingsecondmethod. SRFlip-Flop DFlip-Flop JKFlip-Flop TFlip-Flop SRFlip-Flop SRflip-flopoperateswithonlypositiveclocktransitionsornegativeclocktransitions.Whereas,SRlatchoperateswithenablesignal.ThecircuitdiagramofSRflip-flopisshowninthefollowingfigure. ThiscircuithastwoinputsS&RandtwooutputsQ(t)&Q(t)’.TheoperationofSRflipflopissimilartoSRLatch.But,thisflip-flopaffectstheoutputsonlywhenpositivetransitionoftheclocksignalisappliedinsteadofactiveenable. ThefollowingtableshowsthestatetableofSRflip-flop. S R Q(t+1) 0 0 Q(t) 0 1 0 1 0 1 1 1 - Here,Q(t)&Q(t+1)arepresentstate&nextstaterespectively.So,SRflip-flopcanbeusedforoneofthesethreefunctionssuchasHold,Reset&Setbasedontheinputconditions,whenpositivetransitionofclocksignalisapplied.ThefollowingtableshowsthecharacteristictableofSRflip-flop. PresentInputs PresentState NextState S R Q(t) Q(t+1) 0 0 0 0 0 0 1 1 0 1 0 0 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 x 1 1 1 x ByusingthreevariableK-Map,wecangetthesimplifiedexpressionfornextstate,Q(t+1).ThethreevariableK-Mapfornextstate,Q(t+1)isshowninthefollowingfigure. Themaximumpossiblegroupingsofadjacentonesarealreadyshowninthefigure.Therefore,thesimplifiedexpressionfornextstateQ(t+1)is $Q\left(t+1\right)=S+{R}'Q\left(t\right)$ DFlip-Flop Dflip-flopoperateswithonlypositiveclocktransitionsornegativeclocktransitions.Whereas,Dlatchoperateswithenablesignal.Thatmeans,theoutputofDflip-flopisinsensitivetothechangesintheinput,Dexceptforactivetransitionoftheclocksignal.ThecircuitdiagramofDflip-flopisshowninthefollowingfigure. ThiscircuithassingleinputDandtwooutputsQ(t)&Q(t)’.TheoperationofDflip-flopissimilartoDLatch.But,thisflip-flopaffectstheoutputsonlywhenpositivetransitionoftheclocksignalisappliedinsteadofactiveenable. ThefollowingtableshowsthestatetableofDflip-flop. D Qt+1t+1 0 0 1 1 Therefore,Dflip-flopalwaysHoldtheinformation,whichisavailableondatainput,Dofearlierpositivetransitionofclocksignal.Fromtheabovestatetable,wecandirectlywritethenextstateequationas Q(t+1)=D NextstateofDflip-flopisalwaysequaltodatainput,Dforeverypositivetransitionoftheclocksignal.Hence,Dflip-flopscanbeusedinregisters,shiftregistersandsomeofthecounters. JKFlip-Flop JKflip-flopisthemodifiedversionofSRflip-flop.Itoperateswithonlypositiveclocktransitionsornegativeclocktransitions.ThecircuitdiagramofJKflip-flopisshowninthefollowingfigure. ThiscircuithastwoinputsJ&KandtwooutputsQ(t)&Q(t)’.TheoperationofJKflip-flopissimilartoSRflip-flop.Here,weconsideredtheinputsofSRflip-flopasS=JQ(t)’andR=KQ(t)inordertoutilizethemodifiedSRflip-flopfor4combinationsofinputs. ThefollowingtableshowsthestatetableofJKflip-flop. J K Q(t+1) 0 0 Q(t) 0 1 0 1 0 1 1 1 Q(t)' Here,Q(t)&Q(t+1)arepresentstate&nextstaterespectively.So,JKflip-flopcanbeusedforoneofthesefourfunctionssuchasHold,Reset,Set&Complementofpresentstatebasedontheinputconditions,whenpositivetransitionofclocksignalisapplied.ThefollowingtableshowsthecharacteristictableofJKflip-flop. PresentInputs PresentState NextState J K Q(t) Q(t+1) 0 0 0 0 0 0 1 1 0 1 0 0 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 0 ByusingthreevariableK-Map,wecangetthesimplifiedexpressionfornextstate,Q(t+1).ThreevariableK-Mapfornextstate,Q(t+1)isshowninthefollowingfigure. Themaximumpossiblegroupingsofadjacentonesarealreadyshowninthefigure.Therefore,thesimplifiedexpressionfornextstateQ(t+1)is $$Q\left(t+1\right)=J{Q\left(t\right)}'+{K}'Q\left(t\right)$$ TFlip-Flop Tflip-flopisthesimplifiedversionofJKflip-flop.Itisobtainedbyconnectingthesameinput‘T’tobothinputsofJKflip-flop.Itoperateswithonlypositiveclocktransitionsornegativeclocktransitions.ThecircuitdiagramofTflip-flopisshowninthefollowingfigure. ThiscircuithassingleinputTandtwooutputsQ(t)&Q(t)’.TheoperationofTflip-flopissameasthatofJKflip-flop.Here,weconsideredtheinputsofJKflip-flopasJ=TandK=TinordertoutilizethemodifiedJKflip-flopfor2combinationsofinputs.So,weeliminatedtheothertwocombinationsofJ&K,forwhichthosetwovaluesarecomplementtoeachotherinTflip-flop. ThefollowingtableshowsthestatetableofTflip-flop. D Q(t+1) 0 Q(t) 1 Q(t)’ Here,Q(t)&Q(t+1)arepresentstate&nextstaterespectively.So,Tflip-flopcanbeusedforoneofthesetwofunctionssuchasHold,&Complementofpresentstatebasedontheinputconditions,whenpositivetransitionofclocksignalisapplied.ThefollowingtableshowsthecharacteristictableofTflip-flop. Inputs PresentState NextState T Q(t) Q(t+1) 0 0 0 0 1 1 1 0 1 1 1 0 Fromtheabovecharacteristictable,wecandirectlywritethenextstateequationas $$Q\left(t+1\right)={T}'Q\left(t\right)+TQ{\left(t\right)}'$$ $$\RightarrowQ\left(t+1\right)=T\oplusQ\left(t\right)$$ TheoutputofTflip-flopalwaystogglesforeverypositivetransitionoftheclocksignal,wheninputTremainsatlogicHigh(1).Hence,Tflip-flopcanbeusedincounters. Inthischapter,weimplementedvariousflip-flopsbyprovidingthecrosscouplingbetweenNORgates.Similarly,youcanimplementtheseflip-flopsbyusingNANDgates. PreviousPage PrintPage NextPage  Advertisements