LIN Protocol and Physical Layer Requirements

1 1 SLLA383 February2018 SubmitDocumentationFeedbackCopyright 2018,TexasInstrumentsIncorporatedLIN Protocoland PhysicalLayerRequirementsApplicationRepo rtSLLA383 February2018 LIN Protocoland PhysicalLayerRequirementsEricHackettABST RACTTheLocalInterconnectNetwork(LIN ), ISO17897,is a multipoint,low-cost,easily-implementedco mmunicationbus in automobiles,workingas a sub-busfor theControllerAreaNetworkin integralpartsof LIN technology,with a focuson the LIN transceiveritself,informationon the Protocol ,and the physicallayerrequirementsfor real LIN ,DistanceLimitations,Nodeson of Figures1 LIN Transceiverin SignalThresholdsfor SignalThresholdsfor masternodeMulti CAN bus interfacesMOST bus interfaceDiagnostic Bus InterfaceGateway ModuleLIN Bus#The gateway includes the interfaces with all the buses which typically comprise theVehicle network.

2 The LIN master nose here is configured as part of the different localized control modules connect to the LIN bus are the slave February2018 SubmitDocumentationFeedbackCopyright 2018,TexasInstrumentsIncorporatedLIN Protocoland PhysicalLayerRequirements11 Bus Bus With220 pF, 20 Bus With10 nF, 20 Bus With220 nF, 20 is a registeredtrademarkof LIN othertrademarksare the propertyof automobilescontinueto becomemoreintelligent,safe,and comfortable,the amountof electricalsystemsand componentscontinuesto additionof thesecomponentsand systemscomesaneedfor communicationtransceiversto facilitatetheirinteractionin the mostadvantageousway possiblefor was developedfor this very reason:so car makerscouldmanagecommunicationbetweenthe secomponentsand systemsin an efficient,straightforwardfashion,whereth e bandwidthandversatilityof CANwas not needed;thoughin mostinstances,it is a sub-busto the SpecificationProgressionThe mostup-to-dateLIN standardwas definedin 2010(LIN ,the LIN Consortium).

3 It was thentranscribedto theInternationalOrganizationfor Standardization(ISO)to be acceptedas ISO 17897andofficiallyreleasedin 2010,LIN wentthrougha seriesof revisions,beingfully definedfirst inLIN (1999),wherethe LIN ProtocolSpecification,LIN ConfigurationLanguageSpecification,and LINA pplicationInterfaceSpecificationwereesta blishedby a boardcalledthe LIN theseare necessarypartsin creatingthe full LIN clusterin a way that is consistentacrossthe market,allowingany car manufacturerto use the LIN protocolspecificationdescribesthephysica land datalink layers,and the LIN ConfigurationLanguageenablesthe LIN clusterto be describedin a file that is straightforwardfor any LIN transceiverand its implementationare the focusof this paper.

4 However,it is importantto haveahigh-levelunderstandingof the wholeLIN networkto understandthe placeof the transceiverin LIN becamedefined,it was not only specifiedfor the actual1 s and 0 s datadelivery,butfor a higher-levelnetworkimplementation:The LIN LIN workflowsupportsan easy-to-use,dependableimplementationsche mefor thoseworkingwith the configurationof the entirenetworkclusteris definedand standardized,whichis wheretheLIN DescriptionFile(LDF)comesin. TheSlaveMasterMicrocontrollerSCIM icrocontrollerSCIS laveMicrocontrollerSCIT ransceiverTransceiverTransceiverLIN BusLIN SlaveLIN SlaveLIN SlaveLIN SlaveLIN Slave 2II WKH VKHOI LIN SlaveLIN MasterBusanalyzerEmulatorLIN DescriptionFile (LDF)LIN SlaveLIN SlaveNode CapabilityFiles (NCF)System Defining ToolSystem GeneratorLIN ClusterLIN February2018 SubmitDocumentationFeedbackCopyright 2018,TexasInstrumentsIncorporatedLIN Protocoland PhysicalLayerRequirementsLDF is whatdifferentiatesthe LIN clustersfromeachother,definingthe specificuse and propertiesforthat cluster(nodeamount,amountand the descriptionof messageframes,messagerate,and so forth).

5 This allowsthe generationof softwarefiles by developersto establishwhattask eachnodein the LDF can be usedto automaticallygeneratethe softwareinvolvedin communication,as wellas supplyinformationfor measurementand test toolsinvolvedin the LIN LIN WorkflowThe LDF is writtenusingsyntaxdefinedby theLIN ConfigurationLanguageSpecification. This syntaxisusedin combinationwith theSystemDefiningToolto createthe LDF,and thus definethe thesetools,thereis theLIN NodeCapabilityLanguage, whichallowsthe developerto defineand describethe implementationofOff-the-ShelfNodes, whichare easily-implementable,general-purposeLIN nodesdesignedfor typicalapplicationsthat can be boughtin the LIN BusA LIN clusteris definedas a numberof LIN nodesconnectedthrougha twotypesof nodesin everycluster.

6 One Masternodeand up to 16 masternode,as can be assumedby the name,is whatmanagesthe communicationalongthe bus to theMaster-Slaveprincipleis discussedin High-LevelLIN Transceiverin February2018 SubmitDocumentationFeedbackCopyright 2018,TexasInstrumentsIncorporatedLIN Protocoland PhysicalLayerRequirementsBecausethe wholeidea of LIN is to be a simple,cost-effectivecommunicationinterf ace,a dedicatedcommunicationcontrolleris not microcontrolleris programmedwith the LINprotocol,and usedto drivethe communicationto the transceivervia the interfaceiscalledSerialCommunicationInte rface(SCI)and took the placeof UARTin mostLIN typicalof mostmicrocontrollers,whichallowsfor less workon the backend to LIN bus transmissiononly requiresone wire,and a slowercommunicationspeedis usedin ordertoproperlyhandleany nodesare passivelyconnectedto the bus, and a pullupresistoris usedto ensurethe bus is at the supplyvoltagelevelwhenthe nodesare in the previously-mentionedSCI is the dominantinterfaceusedbetweenLIN transceiversand themicrocontrollersthat communicatewith usedoriginally,but fault-freeinterfacevia UARTis knownto be difficultto microcontrollertransmitsbit frames,startingwith the dominantstartbit.

7 This synchronizesallreceiverson the bus, followedby the leastsignificantbit to mostsignificantbit, thena stop bit. Thisconstitutesone SCI frame,and a LIN messageis composedof multipleSCI everycluster,thereis one masternode,and up to 16 masternodecontrolsallcommunicationon the bus, and containsthe mastertask and the slavetask to be slavenodesare unableto communicatewith eachother,containonly the slavetask,and are only capableofrespondingto the masterif the messageis directedat mastersendsout a requestto adesignatedslaveas a header(beginningof the frame),and the slaverespondsto the masteras also a casewherethe mastersendsthe slavethe headerand responseframe,and the slaveonly listenswith no ,definedbus traffic,disallowingcollisionsalmostalway sbecausethe masteris alwaysinitiatingthe schedulingof the developerof the LIN clusterdoesa properjob planningmessagesand calculatingtheirlengths,aschedulecan be developed,and no collisionswill scheduleis the organizationof messagesframesinto slots,and is whatsets the sendtime of all the messagesto be sent at any (alsoreferredto as requests)

8 Are sent by the masterat thesegiventimesset by the sent to slaves,and the slavecan ignore,respond,or just receivethe tokenand the data(headerand response)are whatmakeup the LIN messages,and up to 64 messagescan bedefinedper problemwith the master-slavesystemis becausethe mastercontrolsall communication,if the masterfails,the schemeswhereall nodescan act as a masterand slave,this doesnothappen,and this qualityis ultimatelywhatkeepsLIN frombeingusedin safety-relatedapplications(that,and the slowmessagerate).The LIN clusteris also not inherentlycapableof event-drivencommunication,becausethe LIN slavescan only communicatewith the bus if they are requestedto do so (speakwhenspokento!)

9 Messagehas a specificstructure:the first part beingthe tokenand the secondpart data(theHeaderand the Response).The tokenis alwaystransmittedby the mastertask,and is dividedup into thesyncbreak,the syncfield,and the protectedidentifier(PID).The syncbreakand syncfield are usedtohaveall the slaveson the LIN bus synchronizedto the mastertiming(withoutthe needof any crystaloroscillator),and the PID is whatdefineswhichslavesrespond,receive,or ignorethe headerin total consistsof at least13 bits for the SYNC break,1 delimiterbit, 10 SYNC field bits (1 startbit, 8 bits for synchronization,and 1 stop bit), and 10 identifierbits (1 startbit, 6 bits forthe identifier,2 bits for parity,and 1 stop bit).

10 SCI FrameSCI FrameFrame HeaderFrame ResponseFrameSCI FrameData Byte 1 Data Byte nChecksumData Field (max. 8 Bytes)SYNC Break FieldSYNC FieldPID FieldSYNC Break:at least 13 bitsSCI Frame : 0x55 SCI FrameFrame HeaderFrame ResponseFrameDELSYNC Break : Synchronization BreakDEL : SYNC Break DelimiterPID : Protected IdentifierSCI : Serial Communication February2018 SubmitDocumentationFeedbackCopyright 2018,TexasInstrumentsIncorporatedLIN Protocoland PhysicalLayerRequirementsFigure5. LIN FrameHeaderExplanationThe Data(response)portionof the messageis sent by the slavetask,whichcan be sent by the masterorthe slavenode,dependingon the PID instruction . The Responseis brokenup into databytes(up to 8),and a checksumis a protectionschemefor the databytes,to verifythat the messagesentis whatwas intended,and no nodecan receivethe frameresponse,whichnodeactuallydoesuse it is dependenton the responsein total consistsof 10bits for eachbyte of data(1 startbit, 8 bits for data,1 stop bit), for up to 8 databytes,and 10 bits forchecksum(1 startbit, 8 bits for checksumsolution,1 stop bit).