英文资料与中文翻译Word格式文档下载.docx

英文资料与中文翻译Word格式文档下载.docx

《英文资料与中文翻译Word格式文档下载.docx》由会员分享，可在线阅读，更多相关《英文资料与中文翻译Word格式文档下载.docx（10页珍藏版）》请在冰豆网上搜索。

英文资料与中文翻译@#@英文资料与中文翻译@#@INTRODUCTION@#@ControllerAreaNetwork（CAN）wasinitiallycreatedbyGermanautomotivesystemsupplierRobertBoschinthemid-1980sforautomotiveapplicationsasamethodforenablingrobustserialcommunication.Thegoalwastomakeautomobilesmorereliable,safeandfuel-efficientwhiledecreasingwiringharnessweightandcomplexity.Sinceitsinception,theCANprotocolhasgainedwidespreadpopularityinindustrialautomationandautomotive/truckapplications.Othermarketswherenetworkedsolutionscanbringattractivebenefitslikemedicalequipment,testequipmentandmobilemachinesarealsostartingtoutilizethebenefitsofCAN.ThegoalofthisapplicationnoteistoexplainsomeofthebasicsofCANandshowthebenefitsofchoosingCANforembeddedsystemsnetworkedapplications.@#@CANOVERVIEW@#@Mostnetworkapplicationsfollowalayeredapproachtosystemimplementation.Thissystematicapproachenablesinteroperabilitybetweenproductfromdifferentmanufacturers.AstandardwascreatedbytheInternationalStandardsOrganization（ISO）asatemplatetofollowforthislayeredapproach.ItiscalledtheISOOpenSystemsInterconnection（OSI）NetworkLayeringReferenceModelandisshowninFigure1forreference.TheCANprotocolitselfimplementsmostofthelowertwolayersofthisreferencemodel.ThecommunicationmediumportionofthemodelwaspurposelyleftoutoftheBoschCANspecificationtoenablesystemdesignerstoadaptandoptimizethecommunicationprotocolonmultiplemediaformaximumflexibility（twistedpair,singlewire,opticallyisolated,RF,IR,etc.）.Withthisflexibility,however,comesthepossibilityofinteroperabilityconcerns.Toeasesomeoftheseconcerns,theInternationalStandardsOrganizationandSocietyofAutomotiveEngineers（SAE）havedefinedsomeprotocolsbasedonCANthatincludetheMediaDependantInterfacedefinitionsuchthatallofthelowertwolayersarespecified.@#@ISO11898isastandardforhigh-speedapplications,ISO11519isastandardforlow-speedapplications,andJ1939（fromSAE）istargetedfortruckandbusapplications.Allthreeoftheseprotocolsspecifya5Vdifferentialelectricalbusasthephysicalinterface.TherestofthelayersoftheISO/OSIprotocolstackarelefttobeimplementedbythesystemsoftwaredeveloper.HigherLayerProtocols（HLPs）aregenerallyusedtoimplementtheupperfivelayersoftheOSIReferenceModel.@#@HLPsareusedto:

@#@@#@1）standardizestartupproceduresincludingbitratesused,@#@2）distributeaddressesamongparticipatingnodesortypesofmessages,@#@3）determinethestructureofthemessages,and@#@4）providesystem-levelerrorhandlingroutines.ThisisbynomeansafulllistofthefunctionsHLPsperform,howeveritdoesdescribesomeoftheirbasicfunctionality.@#@CANPROTOCOLBASICS@#@CarrierSenseMultipleAccesswithCollision@#@Detection（CSMA/CD）@#@TheCANcommunicationprotocolisaCSMA/CDprotocol.TheCSMAstandsforCarrierSenseMultipleAccess.Whatthismeansisthateverynodeonthenetworkmustmonitorthebusforaperiodofnoactivitybeforetryingtosendamessageonthebus（CarrierSense）.Also,oncethisperiodofnoactivityoccurs,everynodeonthebushasanequalopportunitytotransmitamessage（MultipleAccess）.TheCDstandsforCollisionDetection.Iftwonodesonthenetworkstarttransmittingatthesametime,thenodeswilldetectthe‘collision’andtaketheappropriateaction.InCANprotocol,anondestructivebitwisearbitrationmethodisutilized.Thismeansthatmessagesremainintactafterarbitrationiscompletedevenifcollisionsaredetected.Allofthisarbitrationtakesplacewithoutcorruptionordelayofthehigherprioritymessage.@#@Thereareacoupleofthingsthatarerequiredtosupportnon-destructivebitwisearbitration.First,logicstatesneedtobedefinedasdominantorrecessive.Second,thetransmittingnodemustmonitorthestateofthebustoseeifthelogicstateitistryingtosendactuallyappearsonthebus.CANdefinesalogicbit0asadominantbitandalogicbit1asarecessivebit.@#@Adominantbitstatewillalwayswinarbitrationoverarecessivebitstate,thereforethelowerthevalueintheMessageIdentifier（thefieldusedinthemessagearbitrationprocess）,thehigherthepriorityofthemessage.Asanexample,supposetwonodesaretryingtotransmitamessageatthesametime.Eachnodewillmonitorthebustomakesurethebitthatitistryingtosendactuallyappearsonthebus.Thelowerprioritymessagewillatsomepointtrytosendarecessivebitandthemonitoredstateonthebuswillbeadominant.Atthatpointthisnodelosesarbitrationandimmediatelystopstransmitting.Thehigherprioritymessagewillcontinueuntilcompletionandthenodethatlostarbitrationwillwaitforthenextperiodofnoactivityonthebusandtrytotransmititsmessageagain.@#@Message-BasedCommunication@#@CANprotocolisamessage-basedprotocol,notanaddressbasedprotocol