Pojem
Anetworkcomposedofmultipleflip-flopsandmultiplecombinationallogicblocks.Commonlyusedare:counters,complexdataflowcontrollogic,arithmeticcontrollogic,instructionanalysisandoperationcontrollogic.Synchronoussequentiallogicisthecoreofthedesignofcomplexdigitallogicsystems.Sequentiallogicremembersitscurrentstatebymeansofthestatusregister.Indifferentstates,evenifalltheinputsarethesame,theoutputisnotnecessarilythesame.
Úvod do počítačové vědy
Inthefirstfewdecadesaftertheadventofthecomputer,thecomputerwasessentiallyahugecalculator,numberswereentered,andtheresultsofcalculationswereoutput.Itwasnotuntilthe1970sthatscientistsrealizedtheneedtoverifythesecalculationscorrectly.Ascomputersbecomemorepowerfulandsoftwaremoreadvanced,multi-taskingandstrokedataverificationbecomemoredifficult.Therefore,theprogrammerhastoconsiderthebehaviorofthesystemovertime.Underthisopportunity,temporallogicwasintroducedintocomputationalscience,whichwasanimportantturningpointinthehistoryofcomputationalscience.
Sequentiallogicisalsocalledtemporallogic,whichisaveryprofessionalandimportantfieldincomputerscience.Temporallogicisusedtodescribeanysystemthatexpressesandreasoningabouttherulesandsymbolizationoftime-constrainedpropositions,andismainlyusedforformalverification.Inthe1960s,ArthurPriorproposedaspecialtimelogicsystembasedonmodallogicthatwasinvolved.ThistheorywaslaterfurtherdevelopedbylogicianssuchasEmilBernoulli.
Later,PnueliworkedasapostdoctoralfellowatStanfordUniversityandtheIBMWastonResearchCenter.Fromthenon,heshiftedthedirectionofhisworktothefieldofcomputerscience.In1973,hefoundedtheDepartmentofComputerScienceatTelAvivUniversityandservedasthefirstdean.In1977,Pnuelipioneeredtheintroductionoftemporallogicintocomputerscience.Histemporallogicisatypeofnon-classicallogic,studyinghowtodealwithpropositionsandpredicatesofeventsthatcontaintimeinformation.Thecomputersystemnowcommonlyreferredtoassequentiallogicappearedinthisyear,andPnueli'soutstandingcontributiontosub-programminglanguagesandsystemverificationwasamilestone.
"Pnuelirealizedthislogic,whichisaperfectfitforcomputerscience,"saidProfessorMosesofComputingEngineeringatRiceUniversity.Atthe1996TuringAwardCeremony,theaward’sinscriptionevaluatedPnueli’s1977thesis"triggeredashiftinthebasicmodelofsystematicdynamicbehaviorreasoning."Afterthebirthofthisoutstandingtechnology,itcausedasensationinthesoftwareengineeringcommunityandsetoffarevolutioninsoftwareengineering.Ithasbecomeatoolforspecificationandverificationwhendevelopingreactivesystemsandconcurrentsystems.Ithasbeenwidelyusedindesign.
In1981,PnuelireturnedtoWeizmanntobecomeaprofessorintheDepartmentofComputerScience.In1999,PnuelijoinedtheDepartmentofComputerScienceatNewYorkUniversityasaprofessor.Inaddition,likemostprofessorsabroad,Pnueliisnotlimitedtopurelyacademicresearchandteaching.Pnueliestablishedseveralsoftwarecompanies,includingMini-Systemsin1971andAdCadin1984.HealsofoundedanothercompanyinMassachusettswithhisfriends:iLogixInc,PnueliservedasthechiefscientistofiLogixInc.
Pnueliishumbleandeasy-going,andhasadeepconnectionwithChina.HeisclosefriendswithTangZhisong,afamouslogicandsoftwarescientistinmycountrywhodiedin2008,andbothareleadersintheindustryintermsoftemporallogic.ProfessorTangZhisongproposedtheworld'sfirstexecutabletemporallogiclanguageXYZ/E.IfPnueli'sgreatestcontributiontothe1996TuringAwardwasduetothepioneeringintroductionoftemporallogicintocomputationalscience,thenTangZhisongisthefirsttimethatthisformaltheoryoftemporallogiciscombinedwiththelatestsoftwaretechnologytoapplythelanguageThepersonwhointroducesthecontrolmechanismofstatetransitionintothelogicsystem.OntheeveofreceivingtheTuringAwardintheUnitedStates,PnuelisaidinalettertoTangZhisong:"Ifullybelievethatyoushouldsharethishonor(referringtotheTuringAward)becausetenselogichasbecomeaconceptwitha'far-reachingimpact'.Averymeaningfulpart."
InadditiontotheTuringAward,Pnuelihasalsowonnumerousawards,includingtheIsraelAward,whichisIsrael’shighesthonorgiventomembersoftheNationalAcademyofSciencesoftheUnitedStatesofAmerica.
Sekvenční logické obvody
Accordingtothedifferentcharacteristicsoflogicfunctions,digitalcircuitscanbedividedintotwocategories,oneiscalledcombinationallogiccircuits(combinationcircuitsforshort),andtheotheriscalledsequentiallogicCircuit(referredtoassequentialcircuit).Thecharacteristicofthelogicfunctionofthecombinationallogiccircuitisthattheoutputatanytimedependsonlyontheinputatthattime,andhasnothingtodowiththeoriginalstateofthecircuit.Thecharacteristicofsequentiallogiccircuitinlogicfunctionisthattheoutputatanymomentnotonlydependsontheinputsignalatthattime,butalsodependsontheoriginalstateofthecircuit,orinotherwords,isalsorelatedtothepreviousinput.
Úvod
Sequentiallogiccircuitisanimportantpartofdigitallogiccircuit.Sequentiallogiccircuitisalsocalledsequentialcircuit,whichismainlycomposedofstoragecircuitandcombinationallogiccircuit.Itisdifferentfromothercircuitsthatwearefamiliarwith.Itsoutputstateatanytimeisdeterminedbytheinputsignalandtheoriginalstateofthecircuitatthattime,anditsstateismainlymemorizedandrepresentedbythestoragecircuit.Atthesametime,theparticularityofsequentiallogiccircuitsinstructureandfunction,comparedwithothertypesofdigitallogiccircuits,oftenhasthecharacteristicsofgreaterdifficulty,complexcircuitsandawiderangeofapplications[1].
Digitalcircuitsareusuallydividedintotwocategories:combinationallogiccircuitsandsequentiallogiccircuits.Therelevantcontentofcombinationallogiccircuitshasbeenintroducedinthepreviouschapters.Thecharacteristicsofcombinationallogiccircuitsarethattheinputchangesdirectly.Reflectingthechangeofoutput,thestateofitsoutputdependsonlyonthecurrentstateoftheinput,andhasnothingtodowiththeoriginalstateoftheinputandoutput,andthesequentialcircuitisanoutputthatisnotonlyrelatedtothecurrentinput,butalsorelatedtotheoriginalstateofitsoutputstateItisequivalenttoaddingafeedbackinputtotheinputofthecombinationallogic.Thereisastoragecircuitinitscircuit,whichcankeeptheoutputstate.Wecanuseablockdiagramtodescribethecompositionofthesequentialcircuit.
Outputisafunctionofinputandoutputofthestateatthepreviousmoment.Atthistime,itisimpossibletousethemethodofcombinationallogiccircuitfunctionexpressiontoexpressitsoutputfunctionexpression.Thepresentstate(Presentstate)andnextstate(NextState)concept,whenthecurrentstaterepresentsthecurrentstate(usuallyrepresentedbyQn),andthesecondstaterepresentsthestateoftheoutputaftertheinputchanges(usuallyrepresentedbyQn1),thentheinputTheoutputstateafterthechangeisexpressedas
Qn1=f(X,Qn)
kdeXjevstupníproměnná.
Thefollowingtwowaveformdiagramsareusedtohelpestablishtheconceptofmemoryinsequentialcircuits:
TherearefourcaseswheretheinputRSisall0,butthestateoftheoutputQisdifferent.Dependsontheoriginalstateoftheoutput;butthereisanadditionalCP.Atthistime,theoutputQnotonlydependsontheoriginalstateoftheinputRSandtheoutputQ,butalsodependsonthestateoftheCP.OnlywhentheCPishigh,thestateoftheinputcanaffecttheoutputstate.Theabovetwotypesareusuallydividedintotwoformsofmemorycircuits:latchesandflip-flops.ThedifferencebetweenthetwoiswhetherthechangeintheoutputstatedependsontheCP(clockpulse)Pulse).Allcircuitsarecalledlatches,andthecircuitsarecalledflip-flopcircuits.
Characteristicsofsequentiallogiccircuit:Theoutputatanytimenotonlydependsontheinputatthatmoment,butalsoisrelatedtotheoriginalstateofthecircuit,sothesequentialcircuithasamemoryfunction.
Tři druhy logických zařízení
Sekvenční logické obvodyarewidelyused.Theyaredividedaccordingtothedifferentlogicfunctionsrequired,andtherearemanytypesofthem.Inthespecificteachinglinks,threekindsoflogicdevices,whicharewidelyusedandhavethecharacteristicsoftypicalsequentiallogiccircuits,aremainlyselectedforamoredetailedintroduction[1].
1.Počítadlo
Generallyspeaking,thecounterismainlycomposedofflip-flopstocountthenumberofinputcountingpulseCP.Theoutputofthecounterisusuallyafunctionofthecurrentstate.Themaximumnumberofaccumulatedinputpulsesofthecounteriscalledthe"modulus"ofthecounter,whichisrepresentedbyM.Forexample,M=6counter,alsoknownashexadecimalcounter.Therefore,the"modulus"ofthecounterisactuallythenumberofeffectivestatesofthecircuit[1].
Therearemanytypesoflogicdiagramcountersforsynchronousseven-aryadditioncounterswithdifferentcharacteristics.Themainclassificationsareasfollows:Accordingtothecountingsystem,itcanbedividedinto:binarycounter,decimalcounter,andarbitrarysystemcounter.Accordingtothecountingincreaseanddecrease,itcanbedividedinto:additioncounter,subtractioncounter,up/downcounter,alsoknownasreversiblecounter.Accordingtowhethertheflip-flopinthecounterissynchronousornot,itcanbedividedinto:asynchronouscounterandsynchronouscounter[1].
2. Zaregistrujte se
Registerisacircuitthatstoresnumbers,calculationresultsorinstructions.Theshiftregistercannotonlystorenumbers,butalsoundertheactionofshiftpulses,thenumbersintheregistercanbeShiftleftorrightasneeded.Registersandshiftregistersarethebasiclogiccomponentscommonlyusedindigitalsystemsandcomputers,andtheyarewidelyused.Oneflip-flopcanstoreone-bitbinarycode,andnflip-flopscanstoren-bitbinarycode.Therefore,flip-flopsareanimportantpartofregistersandshiftregisters.Theflip-flopsintheregisteronlyrequirethattheyhavethefunctionofsetting0or1.Whetheritisatriggerofasynchronousstructure,atriggerofamaster-slavestructureoranedgetrigger,itcanformaregister[1].
3. Sekvenční pulzní generátor
Sequentialpulsereferstothepulsesignalarrangedinacertainsequenceintimeineachcycleperiod.Thecircuitthatgeneratessequentialpulsesignalsiscalledasequentialpulsegenerator.Indigitalsystems,itisoftenusedtocontrolcertaindevicestoperformoperationsoroperationsinapredeterminedorder[1].
Funkce
Theoutputofthesequentiallogiccircuitatanytimenotonlydependsontheinputatthattime,butalsoisrelatedtotheinputateachtimeinthepast.Commonsequentiallogiccircuitsincludeflip-flops,counters,registers,etc.Asthesequentiallogiccircuithasthefunctionofstorageormemory,itismorecomplicatedtorepair.
Analysisofthemainfailuresofdigitalcircuitswithsequentiallogiccircuits:
1.Clock:Theclockisthesynchronizationsignaloftheentiresystem.Whentheclockfails,itwillcauseoverallfunctionalfailure..Lossofclockpulseswillcausethesystemdatabus,addressbus,orcontrolbustobecomeinactive.Changesintherate,amplitude,width,shape,andphaseoftheclockpulsemaycausemalfunctions.
2.Reset:Devicescontainingamicroprocessor(MPU),eventhesmallestsystem,generallyhavearesetfunction.TheresetpulseisloadedontheMPUwhenthesystemispoweredon,orundercertaincircumstances,theprogramreturnstotheinitialstate(forexample,theWatchdogprogram).Whentheresetpulsecannotoccur,thesignalistoonarrow,thesignalamplitudeisincorrect,thereisinterferenceintheconversion,ortheconversionistooslow,theprogrammaystartatthewrongaddress,resultinginprogramconfusion.
3.Bus:Thebustransfersinstructionseriesandcontrolevents,generallythereareaddressbus,databusandcontrolbus.Whenanerroroccursevenifthereisonlyonebitofthebus,itwillseriouslyaffectthesystemfunctions,causingincorrectaddressing,incorrectdata,orincorrectoperation.Buserrorsmayoccurinthebusdriver,orinothercomponentsthatreceivedatabits.
4.Interrupt:Systemswithmicroprocessors(MPU)aregenerallyabletorespondtointerruptsignalsordevicerequestsandgeneratecontrollogictotemporarilyinterruptprogramexecution,transfertospecialprograms,andserveinterruptdevices.Thenitautomaticallyreturnstothemainprogram.Interrupterrorsaremainlyduetotheadhesionofinterruptlines(thesystemisoperatingveryslowlyatthistime)orinterference(thesystemerrorrespondstointerruptrequests).
5.Signalattenuationanddistortion:Longparallelbusesandcontrollinesmayexperiencecrosstalkandtransmissionlinefailures,manifestedasspikes(crosstalk)onadjacentsignallines,orformationondrivelinesAmplitudereduction(equivalenttomultipleconversionsoflogiclevels),whichmayaddwrongdataorcontrolsignals.Therearemanypossiblereasonsforsignalattenuation,suchashighhumidityenvironments,longtransmissionlines,andhigh-speedconversion.Largeelectronicinterferencesourceswillgenerateelectromagneticinterference(EMI),whichwillcausesignaldistortionandcausecircuitdysfunction.