CAN2.0B-协议规范

BOSCHCANSpecificationVersion2.01991,RobertBoschGmbH,Postfach300240,D-70442StuttgartBOSCHROBERTBOSCHGmbH,Postfach300240,D-70442StuttgartSep.1991page1RecitalTheacceptanceandintroductionofserialcommunicationtomoreandmoreapplicationshasledtorequirementsthattheassignmentofmessageidentifierstocommunicationfunctionsbestandardizedforcertainapplications.TheseapplicationscanberealizedwithCANmorecomfortably,iftheaddressrangethatoriginallyhasbeendefinedby11identifierbitsisenlargedThereforeasecondmessageformat(’extendedformat’)isintroducedthatprovidesalargeraddressrangedefinedby29bits.Thiswillrelievethesystemdesignerfromcompromiseswithrespecttodefiningwell-structurednamingschemes.UsersofCANwhodonotneedtheidentifierrangeofferedbytheextendedformat,canrelyontheconventional11bitidentifierrange(’standardformat’)furtheron.InthiscasetheycanmakeuseoftheCANimplementationsthatarealreadyavailableonthemarket,orofnewcontrollersthatimplementbothformats.InordertodistinguishstandardandextendedformatthefirstreservedbitoftheCANmessageformat,asitisdefinedinCANSpecification1.2,isused.ThisisdoneinsuchawaythatthemessageformatinCANSpecification1.2isequivalenttothestandardformatandthereforeisstillvalid.Furthermore,theextendedformathasbeendefinedsothatmessagesinstandardformatandextendedformatcancoexistwithinthesamenetwork.ThisCANSpecificationconsistsoftwoparts,with•PartAdescribingtheCANmessageformatasitisdefinedinCANSpecification1.2;•PartBdescribingbothstandardandextendedmessageformats.InordertobecompatiblewiththisCANSpecification2.0itisrequiredthataCANimplementationbecompatiblewitheitherPartAorPartB.NoteCANimplementationsthataredesignedaccordingtopartAofthisoraccordingtopreviousCANSpecifications,andCANimplementationsthataredesignedaccordingtopartBofthisspecificationcancommunicatewitheachotheraslongasitisnotmadeuseoftheextendedformat.CANSpecification2.0PARTABOSCHROBERTBOSCHGmbH,Postfach300240,D-70442StuttgartSep.1991PartA-page31INTRODUCTION................................................................................42BASICCONCEPTS............................................................................53MESSAGETRANSFER.....................................................................103.1FrameTypes......................................................................................103.1.1DATAFRAME....................................................................................103.1.2REMOTEFRAME..............................................................................153.1.3ERRORFRAME.................................................................................163.1.4OVERLOADFRAME..........................................................................173.1.5INTERFRAMESPACING...................................................................183.2DefinitionofTRANSMITTER/RECEIVER..........................................204MESSAGEVALIDATION...................................................................215CODING.............................................................................................226ERRORHANDLING...........................................................................236.1ErrorDetection...................................................................................236.2ErrorSignalling...................................................................................237FAULTCONFINEMENT.....................................................................248BITTIMINGREQUIREMENTS..........................................................279INCREASINGCANOSCILLATORTOLERANCE..............................319.1ProtocolModifications........................................................................31ContentsBOSCHROBERTBOSCHGmbH,Postfach300240,D-70442StuttgartSep.1991PartA-page41INTRODUCTIONTheControllerAreaNetwork(CAN)isaserialcommunicationsprotocolwhichefficientlysupportsdistributedrealtimecontrolwithaveryhighlevelofsecurity.Itsdomainofapplicationrangesfromhighspeednetworkstolowcostmultiplexwiring.Inautomotiveelectronics,enginecontrolunits,sensors,anti-skid-systems,etc.areconnectedusingCANwithbitratesupto1Mbit/s.Atthesametimeitiscosteffectivetobuildintovehiclebodyelectronics,e.g.lampclusters,electricwindowsetc.toreplacethewiringharnessotherwiserequired.TheintentionofthisspecificationistoachievecompatibilitybetweenanytwoCANimplementations.Compatibility,however,hasdifferentaspectsregardinge.g.electricalfeaturesandtheinterpretationofdatatobetransferred.ToachievedesigntransparencyandimplementationflexibilityCANhasbeensubdividedintodifferentlayers.•the(CAN-)objectlayer•the(CAN-)transferlayer•thephysicallayerTheobjectlayerandthetransferlayercompriseallservicesandfunctionsofthedatalinklayerdefinedbytheISO/OSImodel.Thescopeoftheobjectlayerincludes•findingwhichmessagesaretobetransmitted•decidingwhichmessagesreceivedbythetransferlayerareactuallytobeused,•providinganinterfacetotheapplicationlayerrelatedhardware.Thereismuchfreedomindefiningobjecthandling.Thescopeofthetransferlayermainlyisthetransferprotocol,i.e.c