英语I2C总线规范21部分Word下载.docx

英语I2C总线规范21部分Word下载.docx

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JANUARY2000

11EXTENSIONSTOTHESTANDARD-MODEI2C-BUSSPECIFICATION

TheStandard-modeI2C-busspecification,withitsdatatransferrateofupto100kbit/sand7-bitaddressing,hasbeeninexistencesincethebeginningofthe1980’s.ThisconceptrapidlygrewinpopularityandistodayacceptedworldwideasadefactostandardwithseveralhundreddifferentcompatibleICsonofferfromPhilipsSemiconductorsandothersuppliers.Tomeetthedemandsforhigherspeeds,aswellasmakeavailablemoreslaveaddressforthegrowingnumberofnewdevices,theStandard-modeI2C-busspecificationwasupgradedovertheyearsandtodayisavailablewiththefollowingextensions:

Fast-mode,withabitrateupto400kbit/s.

High-speedmode（Hs-mode）,withabitrateupto3.4Mbit/s.

10-bitaddressing,whichallowstheuseofupto1024additionalslaveaddresses.

TherearetwomainreasonsforextendingtheregularI2C-busspecification:

Manyoftoday’sapplicationsneedtotransferlargeamountsofserialdataandrequirebitratesfarinexcessof100kbit/s（Standard-mode）,oreven400kbit/s（Fast-mode）.Asaresultofcontinuingimprovementsinsemiconductortechnologies,I2C-busdevicesarenowavailablewithbitratesofupto3.4Mbit/s（Hs-mode）withoutanynoticeableincreasesinthemanufacturing

costoftheinterfacecircuitry.

Asmostofthe112addressesavailablewiththe7-bitaddressingschemeweresoonallocated,itbecameapparentthatmoreaddresscombinationswererequiredtopreventproblemswiththeallocationofslaveaddressesfornewdevices.Thisproblemwasresolvedwiththenew10-bitaddressingscheme,whichallowedaboutatenfoldincreaseinavailableaddresses.

NewslavedeviceswithaFast-orHs-modeI2C-businterfacecanhavea7-ora10-bitslaveaddress.Ifpossible,a7-bitaddressispreferredasitisthecheapesthardwaresolutionandresultsintheshortestmessagelength.Deviceswith7-and10-bitaddressescanbemixedinthesameI2C-bussystemregardlessofwhetheritisanF/S-orHs-modesystem.Bothexistingandfuturemasterscangenerateeither7-or10-bitaddresses.

12FAST-MODE

WiththeFast-modeI2C-busspecification,theprotocol,format,logiclevelsandmaximumcapacitiveloadfortheSDAandSCLlinesquotedintheStandard-modeI2C-busspecificationareunchanged.NewdeviceswithanI2C-businterfacemustmeetatleasttheminimumrequirementsoftheFast-orHs-modespecification（seeSection13）.

Fast-modedevicescanreceiveandtransmitatupto400kbit/s.Theminimumrequirementisthattheycansynchronizewitha400kbit/stransfer;

theycanthenprolongtheLOWperiodoftheSCLsignaltoslowdownthetransfer.Fast-modedevicesaredownward-compatibleandcancommunicatewithStandard-modedevicesina0to100kbit/sI2C-bussystem.AsStandard-modedevices,however,arenotupwardcompatible,theyshouldnotbeincorporatedinaFast-modeI2C-bussystemastheycannotfollowthehighertransferrateand

unpredictablestateswouldoccur.

TheFast-modeI2C-busspecificationhasthefollowingadditionalfeaturescomparedwiththeStandard-mode:

Themaximumbitrateisincreasedto400kbit/s.

Timingoftheserialdata（SDA）andserialclock（SCL）signalshasbeenadapted.ThereisnoneedforcompatibilitywithotherbussystemssuchasCBUSbecausetheycannotoperateattheincreasedbitrate.

TheinputsofFast-modedevicesincorporatespikesuppressionandaSchmitttriggerattheSDAandSCLinputs.

TheoutputbuffersofFast-modedevicesincorporateslopecontrolofthefallingedgesoftheSDAandSCLsignals.

IfthepowersupplytoaFast-modedeviceisswitchedoff,theSDAandSCLI/Opinsmustbefloatingsothattheydon’tobstructthebuslines.

Theexternalpull-updevicesconnectedtothebuslinesmustbeadaptedtoaccommodatetheshortermaximumpermissiblerisetimefortheFast-modeI2C-bus.Forbusloadsupto200pF,thepull-updeviceforeachbuslinecanbearesistor;

forbusloadsbetween200pFand400pF,thepull-updevicecanbeacurrentsource（3mAmax.）oraswitchedresistorcircuit（seeFig.43）.

13Hs-MODE

High-speedmode（Hs-mode）devicesofferaquantumleapinI2C-bustransferspeeds.Hs-modedevicescantransferinformationatbitratesofupto3.4Mbit/s,yettheyremainfullydownwardcompatiblewithFast-orStandard-mode（F/S-mode）devicesforbi-directionalcommunicationinamixed-speedbussystem.WiththeexceptionthatarbitrationandclocksynchronizationisnotperformedduringtheHs-modetransfer,thesameserialbusprotocolanddataformatismaintainedaswiththeF/S-modesystem.Dependingontheapplication,newdevicesmayhaveaFastorHs-modeI2C-businterface,althoughHs-modedevicesarepreferredastheycanbedesigned-intoagreaternumberofapplications.

13.1Highspeedtra