SMI传感器AN05-001应用笔记

SILICONMICROSTRUCTURESINCORPORATEDAN05-001NotesforDigitalCommunicationwithSM5800SeriesPartsAPPLICATIONNOTE2005SMISiliconMicrostructures,Inc.♦1701McCarthyBlvd.♦Milpitas,CA95035♦USATel:408-577-0100♦Fax:[phone]♦[e-mail]♦(I2C)Businterfaceforalldigitalcommunication.UsingtheI2Cbusthecorrecteddigitalpressureanddigitaltemperaturevaluesareaccessedfromonboardmemoryregisters.DIGITALCOMMUNICATIONBASICSTheI2Cbusinterfaceutilizesatwo-wiremethodforcarryinginformationbackandforthbetweenintegratedcircuitdevicesconnectedtothebus.Thetwo-wiremethodiscomprisedofabi-directional,8-bitserialdata(SDA)lineprovidingthepathfordatatransfersandaserialclock(SCL)lineforsynchronizingthedatatransfers.AMasterdeviceintheformofapersonalcomputerormicrocontrollerinitiatesandterminatesdatatransfersontheSDAlineandgeneratestheclocksignalontheSCLline.ASlavedevice(whichrepresentstheSM5800seriesproduct)receivesrequestsfromtheMasterandtransmitsdataaccordingtotherequest.WhenmultipleSlavedevicesareconnectedtothebus,eachSlavemusthaveauniqueaddressandtheMastermustusethisuniqueaddresswhenperformingdatatransferswithaparticularSlave.AdiagramoftheI2CbuswithaMasterandmultipleSlaves(orSM5800parts)isshowninFigure1.MasterSlave1Slave2Slave3Figure1.MultipleSM5800seriesdevicesconnectedtotheI2CbusDATATRANSFERThedatatransferprocessbeginswiththeMasterissuingaSTART(S)command,whichalertsallSlavedevicesofthependingtransferrequest.TheMasterthenspecifieswhichSlavedevicetocommunicatewithandhowthedatawillflowbetweentheMasterandSlave.Next,theMasterwaitsfortheaddressedSlavetorespond.WhenthedesiredSlaveresponds,theMasterandSlavebegintheprocessoftransmittingdatabackandforth.ThetransferprocessendswiththeMasterissuingaSTOP(P)command.Figure2providesadiagramshowingasimpledatatransfersequence.START&STOPCONDITIONSInitiatedbytheMaster,aSTARTconditionedisidentifiedbyaHIGHtoLOWtransitionoftheSDAlinewhilemaintainingastableHIGHconditionontheSCLline.AlldatatransfermustbeginwithaSTARTconditionandthebuslinesareconsideredbusyafteraSTARTconditionisissued.ToendthetransferofdatatheMasterinitiatesaSTOPcondition,whichisidentifiedbyaLOWtoHIGHtransitionoftheSDAlinewhilemaintainingastableHIGHconditionontheSCLline.AN05-001NotesforDigitalCommunicationwithSM5800SeriesPartsAPPLICATIONNOTE2005SMISiliconMicrostructures,Inc.♦1701McCarthyBlvd.♦Milpitas,CA95035♦USATel:408-577-0100♦Fax:[phone]♦[e-mail]♦(LSB)8SLAVEADDRESS(BEGINSWTHMSB)ACKDATA(BEGINSWTHMSB)PACKSCLSDAHIGHLOWHIGHLOWSTARTCONDITIONSTOPCONDITIONBITSBYTECOMPLETE,CLOCKHELDLOWUNITLRECEIVINGDEVICEISREADYFORNEXTOPERATIONFigure2.DiagramofasimpledatatransfersequenceDATAFORMAT&VALIDITYTheSDAlineisan8-bitdigitallineandthisdefinesthesizeofeachbytetransferred.AnacknowledgebitstartswiththeTransmitterreleasingtheSDAlineHIGHatthestartoftheclockcycleimmediatelyfollowingabytetransfer.TheReceivermustthenpulltheSDAlineLOWduringtheHIGHperiodofthesameclockcycle.Theset-upandholdtimesfortheSDAandSCLlinesareprovidedinAPPENDIXA.EverybytetransferredfromTransmittertoReceiverstartswiththemostsignificantbit(MSB).ValiddatatransfersonlyoccurduringtheHIGHperiodoftheSCLclock.IfaReceiverneedstimetocarryoutarequestbeforereceivinganotherbyte,itcanholdtheSCLlineLOW.TodothistheReceiverperformsaninternalinterrupttoholdtheSCLLOW,whichforcestheTransmittertowaitbeforesendingthenextbyte.Whenready,theReceiverreleasestheSCLlineanddatatransfercontinues.ADDRESSINGASLAVEDEVICEAllSlavedevicesmusthaveauniqueidentificationoraddress.ASlaveaddresscannotexceedalengthofsevenbits.TheSlaveaddresssharesspaceintheaddressbytewitharead/writebitandthemaximumlengthoftheaddressbyteiseightbits.Toconstructtheaddressbyte,placetheSlaveaddressattheMSBoftheaddressbyteandplacetheread/writebitattheleastsignificantbit(LSB).TheaddressbytealwaysfollowsaSTARTcondition.WhenanaddressbyteissentovertheSDAline,eachSlavecomparestheMSBofthisbytewithitsownuniqueaddress.TheSlavewiththematchingaddressbecomesactiveandrespondsbysendinganacknowledgebitalongtheSDAlinetotheMaster.HowtheSlaverespondstothenextbytetransmittedbytheMasterfollowingtheacknowledgementdependsontheread/writebit.WhentheLSBoftheaddressbyteis“1”theSlavetransmitsdatafortheMastertoread.WhentheLSBoftheaddressbyteis”0”theSlavewaitsfortheMastertowritedatatotheSlave.SILICONMICROSTRUCTURESINCORPORATEDAN05-001NotesforDigitalCommunicationwithSM5800SeriesPartsAPPLICATIONNOTE2005SMISiliconMicrostructures,Inc.