Introductiontothebus
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( memorias). Dic:a16-bitwideaddressbus (usu-sedin8-bitprocessorsinthe1970sandearly1980s) canaddresse memoria spatii 2tothe 16thpower=65536=64KBaddress, Anda32-bitaddressbus (usually in PCprocessorslikein2004)(canaddresstheadings.
Note: 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.
Workingprinciple
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.
Cubits technical
Thesystembusisacollectionofsignallinesandisacommonchannelfortransmittinginformationbetweenmodules.Throughit,variousdataandcommandscanbetransmittedbetweencomputercomponents.Inordertomaketheproductsofdifferentsuppliersinterchangeableandgiveusersmorechoices,thetechnicalspecificationsofthebusmustbestandardized.Thestandardformulationofthebusmustbecarefullyconsidered,andtheremustbestrictregulations.Systembusstandards(technicalspecifications)include:
(1) Mechanica structurae species: moduli dimensiones, busplugae, connexiones, institutiones dimensivarum regularum unificatarum habent.
(2) Functionalspecification: eachsignalline(nameofthepin), function and working processofeachbusmusthaveunifiedregulations.
(3) Electricalspecifications: theeffectivelevel, dynamicconversiontime, loadcapacity, etc. ofeachsignalline of thebus.
Technicalindicators
1.Thebandwidthofthesystembus (busdatatransferrate)
ThebandwidthofthesystembusreferstothedatatransmittedonthebusperunittimeVolume,thatis,themaximumsteady-statedatatransferrateofMBtransmittedpersecond.Twofactorscloselyrelatedtothebusarethebitwidthofthebusandtheworkingfrequencyofthebus.Therelationshipbetweenthem:thebandwidthofthebus=theworkingfrequencyofthebus*thebitwidthofthebus/8
2,thesystemThebitwidthofthebus
Thebitwidthofthesystembusreferstothenumberofbitsofbinarydatathatthebuscantransmitatthesametime,orthenumberofbitsofthedatabus,thatis,theconceptofbuswidthssuchas32bitsand64bits.Thewiderthebitwidthofthebus,thegreaterthedatatransferratepersecond,andthewiderthebandwidthofthebus.
3.Theworkingfrequencyofthesystembus
TheworkingclockfrequencyofthebusisinMHZ.Thehighertheworkingfrequency,thefasterthebusworkingspeedandthewiderthebusbandwidth.
Developmenthistory
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.