Въведение в автобуса
Theinformationtransmittedonthesystembusincludesdatainformation,addressinformation,andcontrolinformation.Therefore,thesystembusincludesthreebuseswithdifferentfunctions,namelythedatabusDB(DataBus),addressbusAB(AddressBus)andcontrolbusCB(ControlBus).
ThedatabusDBisusedtotransmitdatainformation.Thedatabusisatwo-waythree-stateform(two-waymeansthatitcanbetransmittedintwodirections,A->BorAcanbetransmittedtoothercomponentssuchasmemoryorI/Ointerface,anddataofothercomponentscanalsobetransmittedtotheCPU.Thenumberofbitsofthedatabusisanimportantindicatorofmicrocomputers,usuallyconsistentwiththewordlengthofmicro-processing.Forexample,thewordlengthoftheIntel8086microprocessoris16bits,andthewidthofthedatabusisalso16bits.ItshouldbepointedoutthatthemeaningofdataisInabroadsense,itcanberealdata,instructioncodeorstatusinformation,andsometimesevencontrolinformation.Therefore,inactualwork,thedatatransmittedonthedatabusisnotnecessarilyonlytherealdata.
TheaddressbusABisspeciallyusedtotransferaddresses.SincetheaddresscanonlybetransferredfromtheCPUtotheexternalmemoryorI/Oport,theaddressbusisalwaysone-waythree-state,whichisdifferentfromthedatabus.AddressThenumberofbitsofthebusdeterminesthesizeofthememoryspacethattheCPUcandirectlyaddress.Forexample,iftheaddressbusofan8-bitmicrocomputeris16bits,themaximumaddressablespaceis2^16=64KB,andtheaddressbusofa16-bitmicrocomputeris20Bit,itsaddressablespaceis2^20=1MB.Generallyspeaking,iftheaddressbusisnbits,theaddressablespaceis2^n(2tothepowerofn)addressspaces( memoryunits).Say:a16-bitwideaddressbus(usuallyusedin8-bitprocessorsinthe1970sandearly1980s)canaddressthememoryspaceof2tothe16thpower=65536=64KBaddress,Anda32-bitaddressbus(usuallyinPCprocessorslikein2004)canaddresstheaddressof4,294,967,296=4GB(premise:thewidthofthedatabusis8bits).
Забележка: Bit=bit.
TheBin2^n=X=YGBmentionedaboveisactuallyabit.Thisresultisactuallyobtainedbymultiplyingtheaddressablebitby8bit
ThecontrolbusCBisusedtotransmitcontrolsignalsandtimingsignals.SomeofthecontrolsignalsaresentbythemicroprocessortothememoryandI/Ointerfacecircuits,suchasread/writesignals,chipselectsignals,Interruptresponsesignals,etc.;therearealsoothercomponentsthatfeedbacktotheCPU,suchasinterruptrequestsignals,resetsignals,busrequestsignals,reservereadysignals,etc.Therefore,thetransmissiondirectionofthecontrolbusisdeterminedbythespecificcontrolsignal,whichisgenerallytwo-wayYes,thenumberofbitsofthecontrolbusdependsontheactualcontrolneedsofthesystem.Infact,thespecificsituationofthecontrolbusmainlydependsontheCPU.
Принцип на работа
ThesystembusisinthemicrocomputerThecentralpositionislikethehumannervecentersystem.TheCPUreadsandwritesthecontentsofthememorythroughthesystembus.Alsothroughthebus,thedataintheCPUiswrittentotheperipherals,ortheperipheralsarereadintotheCPU.Microcomputersallusebuses.Structure.ThebusisasetofcommunicationLetterline.Themicrocomputerconnectsthecomponentstogetherthroughthesystembus,andrealizestheinformationexchangebetweenthecomponentsinsidethemicrocomputer.Ingeneral,thesignalprovidedbytheCPUneedstopassthroughthebusformingcircuittoformasystembus.Thesystembusisdividedaccordingtothefunctionoftransmittinginformation,whichisdividedintoaddressbus,databusandcontrolbus.Thesebusesprovidetheconnectionlinesbetweenthemicroprocessor(CPU)andthememoryandinputandoutputinterfacecomponents.ItcanbeconsideredthatamicrocomputerisbasedontheCPU,andothercomponentsareall"connected"onthesystembusconnectedtotheCPU.Thiskindofbusstructureprovidesconvenienceforcomposingamicrocomputer.Peoplecanconnectdifferentsizesofmemoryandinterfacestothesystembusaccordingtotheirownneeds,anditiseasytoformmicrocomputersofvarioussizes.
ThemicrocomputeressentiallyconnectstheCPU,memoryandinput/outputinterfacecircuittothesystembuscorrectly,andthehardwaredesignofthecomputerapplicationsystemisessentiallythebusinterfacebetweentheexternaldeviceandthesystembus.Circuitdesignproblem,thiskindofbusstructuredesignisacharacteristicofcomputerhardwaresystem.
Commonbus
ISAbus
----ISA(industrialstandardarchitecture)busstandardwasestablishedbyIBMin1984fortheintroductionofPC/ATmachinesThesystembusstandard,soitisalsocalledATbus.ItisanextensionoftheXTbustomeettherequirementsofthe8/16-bitdatabus.Itwaswidelyusedinthe80286to80486era,sothattheISAbusslotwasstillreservedinthePentiummachine.TheISAbushas98pins.
EISAbus
----EISAbusisabusstandardjointlylaunchedby9companiessuchasCompaqin1988.Itusesadouble-layersocketonthebasisoftheISAbus,and98signallinesareaddedtothe98signallinesoftheoriginalISAbus,thatis,anEISAsignallineisaddedbetweenthetwoISAsignallines.Inpractice,theEISAbusisfullycompatiblewithISAbussignals.
VESAbus
----VESA(videoelectronicsstandardassociation)busisalocalbusjointlylaunchedby60accessorycardmanufacturersin1992,referredtoasVL(VESAlocalbus)bus.Itsintroductionlaidthefoundationfortheinnovationofthemicrocomputersystembusarchitecture.ThisbussystemtakesintoaccountthedirectconnectionbetweentheCPU,themainmemoryandtheCache.UsuallythispartofthebusiscalledtheCPUbusorthemainbus,andotherdevicesareconnectedtotheCPUbusthroughtheVLbus,sotheVLbusiscalledthelocalbus.Itdefinesa32-bitdatalineandcanbeexpandedto64-bitthroughanexpansionslot.Itusesa33MHzclockfrequencyandhasamaximumtransferrateof132MB/s,whichcanworksynchronouslywiththeCPU.Itisahigh-speed,high-efficiencylocalbusthatcansupport386SX,386DX,486SX,486DXandPentiummicroprocessors.
PCIbus
----PCI(peripheralcomponentinterconnect)busisoneofthemostpopularbusesatpresent.ItisalocalbuslaunchedbyIntelCorporation.Itdefinesa32-bitdatabusandcanbeexpandedto64bits.ThePCIbusmotherboardslotissmallerthantheoriginalISAbusslot,anditsfunctionisgreatlyimprovedthanVESAandISA.Itsupportsburstreadandwriteoperations,andthemaximumtransferratecanreach132MB/s.Itcansupportmultiplesetsofperipheralsatthesametime.equipment.ThePCIlocalbusisnotcompatiblewiththeexistingISA,EISA,andMCA(microchannelarchitecture)buses,butitisnotrestrictedbytheprocessorandisabusdevelopedbasedonanewgenerationofmicroprocessorssuchasPentium.
CompactPCI
----ThesystembuseslistedabovearegenerallyusedincommercialPCs.Inthecomputersystembus,thereisanothermajorcategory:Systembusdesignedtoadapttotheindustrialfieldenvironment,suchasSTDbus,VMEbus,PC/104bus,etc.Hereonlyintroducesoneofthepopularbusesofthecurrentindustrialcomputer-CompactPCI.
----CompactPCImeans"solidPCI".ItisthefirstPCIsystemthatadoptsapassivebusbackplanestructure.ItisanindustrythatusestheelectricalandsoftwarestandardsofthePCIbusandEuropean-stylecards.Theassemblystandardisthelatestindustrialcomputerstandard.CompactPCIisbasedontheoriginalPCIbus.ItusestheadvantagesofPCItoprovideahigh-performancecoresystemthatmeetstheapplicationrequirementsofindustrialenvironments.Atthesametime,italsoconsidersmakingfulluseoftraditionalbusproducts,suchasISA,STD,VMEorPC/104toexpandtheI/Oandotherfunctionsofthesystem.
----6.PCI-Ebus
----PCIExpressusesthepoint-to-pointserialconnectionpopularintheindustry,comparedtoPCIandearliercomputersThesharedparallelarchitectureofthebus,eachdevicehasitsowndedicatedconnection,doesnotneedtorequestbandwidthfromtheentirebus,andcanincreasethedatatransmissionratetoaveryhighfrequency,reachingthehighbandwidththatPCIcannotprovide.ComparedwiththetraditionalPCIbusthatcanonlyachieveone-waytransmissioninasingletimeperiod,thedual-simplexconnectionofPCIExpresscanprovideahighertransmissionrateandquality.Thedifferencebetweenthemissimilartohalf-duplexandfull-duplex.
Технически спецификации
Thesystembusisacollectionofsignallinesandisacommonchannelfortransmittinginformationbetweenmodules.Throughit,variousdataandcommandscanbetransmittedbetweencomputercomponents.Inordertomaketheproductsofdifferentsuppliersinterchangeableandgiveusersmorechoices,thetechnicalspecificationsofthebusmustbestandardized.Thestandardformulationofthebusmustbecarefullyconsidered,andtheremustbestrictregulations.Systembusstandards(technicalspecifications)include:
(1) Спецификации на механичната структура: размерите на модула, щепселите за шини, съединителите за шини и размерите за инсталиране имат унифицирани разпоредби.
(2) Функционална спецификация: всяка сигнална линия (име на щифта), функция и работен процес на всяка шина трябва да има унифицирани разпоредби.
(3) Електрически спецификации: ефективно ниво, време за динамично преобразуване, капацитет на натоварване и т.н. на всеки сигнал от линията на шината.
Технически показатели
1.Ширината на честотната лента на системната шина (трансфер на данни по шина)
ThebandwidthofthesystembusreferstothedatatransmittedonthebusperunittimeVolume,thatis,themaximumsteady-statedatatransferrateofMBtransmittedpersecond.Twofactorscloselyrelatedtothebusarethebitwidthofthebusandtheworkingfrequencyofthebus.Therelationshipbetweenthem:thebandwidthofthebus=theworkingfrequencyofthebus*thebitwidthofthebus/8
2,систематаБитовата ширина нашината
Thebitwidthofthesystembusreferstothenumberofbitsofbinarydatathatthebuscantransmitatthesametime,orthenumberofbitsofthedatabus,thatis,theconceptofbuswidthssuchas32bitsand64bits.Thewiderthebitwidthofthebus,thegreaterthedatatransferratepersecond,andthewiderthebandwidthofthebus.
3. Работната честота на системната шина
TheworkingclockfrequencyofthebusisinMHZ.Thehighertheworkingfrequency,thefasterthebusworkingspeedandthewiderthebusbandwidth.
История на развитието
Thedetaileddevelopmenthistoryofthecomputersystembus,includingtheearlyPCbusandISAbus,PCI/AGPbus,PCI-XbusandthemainstreamPCIExpress,HyperTransporthigh-speedstringLinebus.FromPCbustoISA,PCIbus,andthenfromPCItoPCIExpressandHyperTransportsystem,thecomputerhasalsocompletedthreeleap-typeupgradesduringthesethreemajortransitions.Correspondingtothisprocess,thecomputer'sprocessingspeed,realizedfunctions,andsoftwareplatformareallundergoingthesameevolution.Obviously,withouttheadvancementofbustechnologyasafoundation,therapiddevelopmentofcomputersisimpossibletotalkabout.Theindustrystandsatanewstartingpoint:PCIExpressandHyperTransporthavecreatedanearlyperfectbusarchitecture.Theindustry'sdesireforhigh-speedbusesisendless.PCIExpress4.0andHyperTransport4.0havebeenputontheagenda,andtheywillonceagainbringperformanceimprovements.Inacomputersystem,variousfunctionalcomponentsexchangedatathroughthesystembus,andthespeedofthebushasagreatimpactonsystemperformance.Andbecauseofthis,thebusisknownasthenervecenterofthecomputersystem.ButcomparedtofunctionalcomponentssuchasCPU,graphicscard,memory,harddisk,etc.,thepaceofimprovementofbustechnologyismuchslower.InthehistoryofPCdevelopmentformorethan20years,thebushasonlybeenupdatedthreetimes,buteachchangeofithasbroughtanewlooktothecomputer.