英文资料与中文翻译.docx
- 文档编号:2421975
- 上传时间:2022-10-29
- 格式:DOCX
- 页数:10
- 大小:27.97KB
英文资料与中文翻译.docx
《英文资料与中文翻译.docx》由会员分享,可在线阅读,更多相关《英文资料与中文翻译.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
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 英文 资料 中文翻译
![提示](https://static.bdocx.com/images/bang_tan.gif)