CAN通讯协议介绍

会计学1CAN通讯协议介绍2Agenda

Part1:LearnthehighlevelCANfeatures

Part2:UnderstandtheCANmessage

Part3:UnderstandhowmessagesarecommunicatedbetweenCANnodes第1页/共62页3Part1:

TheBigPicture第2页/共62页4WhatisCAN?Standsfor:Controller–AreaNetwork

DevelopmentoftheCAN-busstartedoriginallyin1983atRobertBoschGmbH

Theprotocolwasofficiallyreleasedin1986attheSocietyofAutomotiveEngineers(SAE)congressinDetroit第3页/共62页5CANKeyFeaturesSpeedupto1MbpsNon-destructivemessagearbitrationAllnodesreceiveallmessagesNoguaranteedmessagelatency第4页/共62页6CostvsDataRateLINCANFlexRayMOST12510RelativecostpernodeDatarate[bps]20K1M10M25M第5页/共62页7CANvsLINCANismuchfaster:upto1MbpsLINoffersatimedeterministicmodelCANoffersamorepowerfulchecksumUsesLDFinsteadofDBCfilesfordatabases第6页/共62页8CANvsFlexRayFlexRaynetworkstartupmorecomplicatedFlexRayofferstimedeterministiccommunicationsFlexRayoffersfaulttoleranceusingvariousmechanismsFlexRayofferslargerdataframesUsesFIBEXinsteadofDBCfiles第7页/共62页9CANvsMOSTMOSTistargetedatinfotainmentapplicationsMOSToffersdedicatedtransfersinaringnetworkat25MbpsOptical,50MbCopper,and150Mbpsopticalphysicallayers第8页/共62页10CANHardwareFeaturesModeratecostsiliconimplementationRequireshardwareCANcontrollerandCANtransceiverRequireshardwareCANtransceiverMicroprocessorCAN

TransceiverCANControllerCANHighCANLowGround第9页/共62页11Quiz11.CANguaranteesmessagelatency.

(TrueorFalse)‏2.CANrequireshardwarecontrollers.

(TrueorFalse)‏3.CANissimilartoLIN:bothhaveverydefinedmessagestructure.

(TrueorFalse)‏4.Whatisthemaximumnumberofbytes

canbeinaCANmessage?第10页/共62页12CANPhysicalLayersHighSpeedCAN:upto1MbpsLowSpeedFaultTolerantCAN:

upto125kbpsSingleWireCAN:upto83.3kbps第11页/共62页132.53.5V1.5tCANHighCANLowRecessiveDominantCANDualWirePhysicalLayers

第12页/共62页14CANNode1CANNode2CANNode3120Ohm120OhmCANDualWireTermination第13页/共62页15SingleWirePlusGroundTwo120OhmterminationresistorsBuslengthto40meters@1Mbps,Slower=longer.SWPhysicalLayer第14页/共62页16DW/LSFTPhysicalLayerTwistedPair(CANH/CANL)plusGroundTwo120OhmterminationresistorsBuslengthto40meters@1Mbps,Slower=>longer.第15页/共62页17CANSupportMultipleversionsofCANaresupportedinValueCANandneoVIFIRE:HighSpeedCAN,LSFTCAN,SingleWireCANVehicleSpyprovidesfullCANsupport:

CANmessageandsignaldecoding,

logging,CANnodesimulation第16页/共62页18Lab1:ObjectivesGetfamiliarwithIntrepidCAN/LINboardFindUSBpowerconnectorFindCANandneoVIpowerconnectorLocateLINandCANtransceiverson

theboardConnectUSBandpowercablesConnectneoVItotheboard第17页/共62页19IntrepidCAN/LINBoardTwoidenticalconnectedCANnodesPowerissuppliedthroughUSBCANconnectorsforneoVIandValueCANPowerconnectorforneoVI第18页/共62页20IntrepidBoardTwoCANtransceiverswithtestpointsTworesetbuttons第19页/共62页21Quiz21.CANbusrequiresterminationof1200Ohm

(TrueorFalse)‏2.CANrequiresthreelines:CANlow,CANHighandground

(TrueorFalse)‏3.SinglewireCANisingeneraltheslowestCANtype.

(TrueorFalse)‏第20页/共62页22Part2:

TheCANmessage第21页/共62页23CANDataFrameTypicalCANmessageiscalleddataframeNumberofdatabytes:0-8CANDataFrameProtocolOverheadDataBytesProtocolOverhead第22页/共62页24CANFrameFieldsArbitrationfieldrepresentsframeIDControlfieldhasdefinesframelengthCRCstandsforCyclicRedundancyCheck:

thisisCANframechecksumACKisacknowledgefield:confirmsframereceptionCANDataFrameDataBytesArbitrationFieldControl

FieldCRCACK第23页/共62页25ArbitrationFieldIdentifierassigns11bitIDtoCANframesRemoteTransmitRequest(RTR)bitCANnodesendsCANframewithrecessiveRTRbit(logical1)whenthenoderequestsdatafrom

othernodesDataBytesControl

FieldIdentifierRTR111ArbitrationFieldCRCACK第24页/共62页26CANRemoteFrameIdenticaltotheDataFrame,except

thereisnodatabytesRTRbitisrecessive(logical1)‏Control

FieldCRCACKArbitrationField第25页/共62页27ControlFieldDLCspecifiesnumberofdatabytes:0-8RB0bitissettological0andreservedforthefutureprotocolsIDEbitdefinesdataframetype:standardIDorextendedIDdataframeIDEbits:dominantforstandardandrecessiveforextendeddataframeDataBytesIdentifierIDEControlField114RB0DLCCRCACK第26页/共62页28ExtendedDataFrameSimilartostandarddataframeIdentifieris29bitslongIdentifierissplitintotwoparts:ID1andID2Data

BytesSRR1111181IDEID1CRCACKID2RTRArbitrationFieldControl

Field第27页/共62页29StandardandExtendedFramesDataBytesControl

FieldIdentifierRTR111CRCACKData

BytesSRR1111181IDEID1CRCACKID2RTRArbitrationFieldControl

FieldArbitrationField第28页/共62页30CRCFieldCRC:CyclicRedundancyCheckCRCiscalculatedandputonthebusbytransmittingnodeCRCiscomputedagainbythereceivingnode:ifitdoesnotmatch,thenanerrorframeissentandthedataframeissentagainbythetransmitter.CRCfieldis15bitlongandhas1bitdelimiterDelimiteralwaysshouldbelogical1DataBytesArbitrationFieldControl

FieldCRCACKDel第29页/共62页31ACKFieldACK:AcknowledgefieldIfCANnodereceivedthemessagecorrectlyitshouldsetACKbitasdominantbit(logical0)AtleastonereceivershouldsetACKtodominantbit.Ifnot,anerrorframeifgeneratedand

thetransmitterresendstheframeACKdelimiter:1bitalwaysshouldbelogical1DataBytesArbitrationFieldControl

FieldCRCACKDelDel第30页/共62页32Lab2:ObjectivesGetfamiliarwithWaveBPSsoftwareConnectedWaveBPStoIntrepidboardusingtheoscilloscopeRunWaveBPSandmonitorCANwaveformscomingfromtheboardIdentifyCANhighandCANlowlinesMeasureonebitlengthintimeandcomputecorrespondingCANbaudrate第31页/共62页33Quiz3Whatisthemaindifferencebetweenaremoteframeandadataframe?ControlfieldcontainsthenumberofCANdatabytes(TrueorFalse)‏3.WhatisthemaindifferencebetweenastandardandextendedCANframes?4.IfanodereceivedaCANframecorrectly,howwouldthisaffectACKfieldoftheframe?第32页/共62页34Part3:

Messagesendingandreceiving第33页/共62页35CANArbitrationAnynodecantransmitwhenbusisfreeMultiplenodetransmissionisresolvedbybitwisearbitrationusingIDfieldNondestructiveframearbitration第34页/共62页36CANArbitrationHigherpriorityframeswinarbitrationDataframeswinarbitrationoverremoteframesNodesalwaysmonitorthebusIfthereisadominantbitonthebus,andanodewantstosendarecessivebit,thenodelosesarbitration第35页/共62页371011001101110110010011LSBMSBNodewantstosendCANframewiththisID:OthernodeID:CANArbitrationExample第36页/共62页38StartandEndofFrameAlldataandremoteframeshavestartand

endwaveformsStartofframeis1dominantbitEndofframe(EOF)is7recessivebitsIntermissionfieldis3recessivebits:overloadframecanbesentduringthefirstintermissionbitCANDataorRemoteFrameStartBitEOFINTIdle

Bus第37页/共62页39OverloadFrameOverloadframeissentwhenreceiverrequires

adelay,orDominantbitwasdetectedduringintermissonAtmosttwooverloadframescanbegeneratedtodelaynextdataorremoteframeOverloadflagfromnodesis6bitshighOverloadframeSuperpositionofoverloadflagsfromnodes(6bitsdom.)‏Delimiter6-12bits8bitsHighEOF第38页/共62页40ErrorFrameErrorframeissentwhenanodedetects

errorconditiononthebusActiveErrorflagfromnodesis6bitshighErrorframeSuperpositionofoverloadflagsfromnodes(6bitsdom.)‏Delimiter6-12bits8bitsHighEOF第39页/共62页41ChecksumErrorCRCiscomputedbytransmitterandputonthebusReceivingnodecalculatesCRCandcomparesit

withCRCfieldIfCRCdoesnotmatch,errorframeisgeneratedandtransmitterresendsthemessageCANDataFrameDataBytesArbitrationFieldControl

FieldCRCACK第40页/共62页42AcknowledgeErrorAtleastonereceivermustsetACKbitdominantIfnot,anerrorframeisgeneratedandthetransmitterresendsthemessageDataBytesArbitrationFieldControl

FieldCRCDelACK第41页/共62页43FormErrorCondition:fixedformfieldshaveillegalbits:dominantbit(logical0)isdetectedinthedelimiters,EndofFrame(EOF)orinter-framespaceTransmitterthensenderrorframeandresendsthemessageCANDataorRemoteFrameEOFINTIdle

BusDelDel第42页/共62页44StuffErrorCondition:6consecutivebitsofthesamestateinnon-fixedformfieldsCANbitstuffingalgorithminsertsadditionalbitsintoCANframetomakesurethereisnomorethan5consecutivebitsofthesamelevelThetransmitterresendsthemessageCANDataFrameDataBytesArbitrationFieldControl

FieldCRCACK第43页/共62页45BitErrorCondition:transmittermonitorswhatitsendsanddetectsabitstateoppositetowhatitputonthebusExcludeArbitrationandACKfieldCANDataFrameDataBytesArbitrationFieldControl

FieldCRCACK第44页/共62页46FaultConfinement

Whathappenswhentransmitterdetectsanerrorandkeepssendingerrorframes?Endlessloopproblem:transmittersendsbadframeandthereceivererrorframesitSolution:nodefaultconfinement.ItmaintainsCANTXandRXerrorcounters,andisolatenodesfromthecommunicationaftercertainnumbersoferrors第45页/共62页47FaultConfinementStatesThreestatesErroractivenodes:takepartinthecommunicationandsenderroractiveflagswhenerrorsaredetectedErrorpassivenodes:takepartinthecommunicationbutcanonlysenderrorpassiveflagsAftertransmission,errorpassivenodessendadditional8recessivebitsafterintermissionfield–itiscalled“SuspendTransmission”fieldBusoffnodes:noinfluenceonthebus第46页/共62页FaultConfinementErrorCountersTEC:000REC:000ErrorActiveErrorActiveREC:001TEC:000REC:002TEC:001REC:003TEC:002REC:004TEC:004REC:010TEC:011REC:018TEC:026REC:029TEC:052REC:029TEC:097REC:031TEC:129REC:033TEC:185REC:042TEC:211REC:047TEC:233REC:051TEC:256ErrorCountersTEC:000REC:000REC:000TEC:000ErrorCountersTEC:000REC:000REC:001TEC:000REC:000TEC:000REC:001TEC:000REC:002TEC:000REC:001TEC:000REC:002TEC:0003ErrorStates:ErrorActive,ErrorPassive,BusOffCANNode1CANNode2CANNode3ErrorActiveErrorPassiveBUSOFF第47页/共62页49ReceiveErrorCounterIfreceiversendsanerrorframe:REC+1

Ifreceiverwasfirsttostartanerrorframe:

REC+8

IfreceivermonitorsaBITERRORwhilesendinganerrorframe:

REC+8

Aftersuccessfullyreceivingamessage:

REC-1

第48页/共62页50TransmitErrorCounterIftransmittersendsanerrorframe:TEC+8

IftransmittermonitorsaBITERRORwhilesendinganerrorframe:

TEC+8

Aftersuccessfullytransmittingamessage:

TEC-1

IfTECreaches127:

CannotsendErrorFrames,butcanTx/Rx第49页/共62页51Lab3:ObjectivesGetfamiliarwithVehicleSpysoftwareCreateamessagethatissentperiodicallyPutthatmessageintothe2ndnodeontheEVBFindourmessageamongstallthemessages第50页/共62页52Quiz4Overloadframeissentwhenreceiverrequiresadelay.

(TrueorFalse)‏2.Underwhatconditionsdoesaformerroroccur?3.Stuffbitsareinsertedonlyifthereare5consecutivebitsofthesamestateonthebus.

(TrueorFalse)‏第51页/共62页53CANArbitrationAnynodecantransmitwhenbusisfreeMultiplenodetransmissionisresolvedbybitwisearbitrationusingIDfieldNondestructiveframearbitration第52页/共62页54CANArbitrationHigherpriorityframeswinarbitrationDataframeswinarbitrationoverremoteframesNodesalwaysmonitorthebusIfthereisadominantbitonthebus,andanodewantstosendarecessivebit,thenodelosesarbitration第53页/共62页551011001101110110010011LSBMSBNodewantstosendCANframewiththisID:OthernodeID:CANArbitrationExampl