Introduction to the Controller Area Network (CAN) (Rev. B)

1 1 SLOA101B August2002 RevisedMay 2016 SubmitDocumentationFeedbackCopyright 2002 2016,TexasInstrumentsIncorporatedIntrodu ctionto the ControllerAreaNetwork (CAN) CANopenis a trademarkof CANin a trademarkof OpenDeviceNetVendorAssociation, August2002 RevisedMay 2016 Introductionto the ControllerAreaNetwork(CAN) controllerareanetwork (CAN) is ideallysuitedto the manyhigh-levelindustrialprotocolsembraci ngCANand ISO-11898:2003as cost,performance,and upgradeabilityprovidefortremendousflexib ilityin introductionto the CANfundamentals,operatingprinciples.

2 And the implementationof a basicCANbus with TI's CANtransceiversand electricallayerrequirementsof a CANbus are discussedalongwith the importanceof thedifferentfeaturesof a TI Bit Fieldsof StandardCANand of Figures1 The LayeredISO InvertedLogicof a a a RecessiveBus of TablesDSPor ControllerApplication LayerData-LinkLayerLogic Link ControlMedium AccessControlPhysicalLayerPhysical SignalingPhysical Medium AttachmentMedium-Dependant InterfaceEmbeddedCANC ontrollerCANT ransceiverCAN Bus-LineElectricalSpecifications:Transce ivers,Connectors,CableCAN Controller ,Embedded August2002 RevisedMay 2016 SubmitDocumentationFeedbackCopyright 2002 2016,TexasInstrumentsIncorporatedIntrodu ctionto the ControllerAreaNetwork(CAN)(1)RobertBosch GmbH, CANbus was developedby BOSCH(1)as a multi-master,messagebroadcastsystemthat specifiesamaximumsignalingrate of 1 megabitper second(bps).

3 Unlikea traditionalnetworksuchas USBorEthernet,CANdoesnot sendlargeblocksof datapoint-to-pointfromnodeA to nodeB underthesupervisionof a centralbus a CANnetwork,manyshortmessageslike temperatureor RPMare broadcastto the entirenetwork,whichprovidesfor dataconsistencyin everynodeof the messageformat,messageidentifiers,and bit-wisearbitration-- a majorbenefitof the CANsignalingschemeare explained,a CANbus implementationis examined,typicalwaveformspresented,and CANS tandardCANis an InternationalStandardizationOrganization (ISO)definedserialcommunicationsbus originallydevelopedfor the automotiveindustryto replacethe complexwiringharnesswith a two-wirebus.

4 Thespecificationcallsfor high immunityto electricalinterferenceand the abilityto self-diagnoseand to CAN s popularityin a varietyof industriesincludingbuildingautomation,me dical,and CANcommunicationsprotocol,ISO-11898:2003 ,describeshow informationis passedbetweendeviceson a networkand conformsto the OpenSystemsInterconnection(OSI)modelthat is definedintermsof the physicalmediumis definedbythe physicallayerof the ISO 11898architecturedefinesthe lowesttwo layersof the sevenlayerOSI/ISOmodelas the data-linklayerand physicallayerin The LayeredISO 11898 StandardArchitectureIn Figure1, the applicationlayerestablishesthe communicationlink to an upper-levelapplicationspecificprotocolsu chas the vendor-independentCANopen protocolis supportedby theinternationalusersand manufacturersgroup,CANin Automation(CiA).

5 AdditionalCANinformationislocatedat the CiA Website, Manyprotocolsare dedicatedto particularapplicationslikeindustrialauto mation,dieselengines,or industry-standard,CAN-basedprotocolsare KVASER'sCANK ingdomand RockwellAutomation'sDeviceNet . Bytes DataCCRRCCACKEOFEOFEOFFISIIDDEErr00 DDLLCC1 1- b itId e n tifie ExtendedCAN3 SLOA101B August2002 RevisedMay 2016 SubmitDocumentationFeedbackCopyright 2002 2016,TexasInstrumentsIncorporatedIntrodu ctionto the ControllerAreaNetwork (CAN) 3 StandardCANor ExtendedCANThe CANcommunicationprotocolis a carrier-sense,multiple-accessprotocolwit h collisiondetectionandarbitrationon messagepriority(CSMA/CD+AMP).

6 CSMA meansthat eachnodeon a bus mustwait for aprescribedperiodof inactivitybeforeattemptingto senda +AMPmeansthat collisionsareresolvedthrougha bit-wisearbitration,basedon a preprogrammedpriorityof eachmessagein theidentifierfield of a higherpriorityidentifieralwayswinsbus , the last logic-high in the identifierkeepson transmittingbecauseit is the a bustakespart in writingeverybit "as it is beingwritten,"an arbitratingnodeknowsif it placedthe logic-highbiton the ISO-11898:2003 Standard,with the standard11-bitidentifier,providesfor signalingratesfrom125kbpsto 1 standardwas lateramendedwith the extended standard11-bitidentifierfield in Figure2 providesfor 211, or 2048differentmessageidentifiers,whereast he extended29-bit identifierin Figure3 providesfor 229, or 537 Bit Fieldsof StandardCANand StandardCAN:11-BitIdentifierThe meaningof the bit fieldsof Figure2 are.

7 SOF The singledominantstartof frame(SOF)bit marksthe startof a message,and is usedtosynchronizethe nodeson a bus afterbeingidle. Identifier-TheStandardCAN11-bitidentifie restablishesthe priorityof the lowerthebinaryvalue,the higherits priority. RTR The singleremotetransmissionrequest(RTR)bit is dominantwheninformationis nodesreceivethe request,but the identifierdeterminesthe also receivedby all nodesand usedby any this way,all databeingusedin a systemis uniform. IDE A dominantsingleidentifierextension(IDE)bi t meansthat a standardCANidentifierwith noextensionis beingtransmitted.

8 R0 Reservedbit (for possibleuse by futurestandardamendment). DLC The 4-bitdatalengthcode(DLC)containsthe numberof bytesof databeingtransmitted. Data Up to 64 bits of applicationdatamay be transmitted. CRC The 16-bit(15 bits plus delimiter)cyclicredundancycheck(CRC)cont ainsthe checksum(numberof bits transmitted)of the precedingapplicationdatafor errordetection. ACK Everynodereceivingan accuratemessageoverwritesthis recessivebit in the originalmessagewith a dominatebit, indicatingan error-freemessagehas receivingnodedetectanerrorand leavethis bit recessive,it discardsthe messageand the sendingnoderepeatsthe this way,eachnodeacknowledges(ACK)the integrityof its 2 bits,one is the acknowledgmentbit and the secondis a delimiter.

9 EOF This end-of-frame(EOF),7-bitfield marksthe end of a CANframe(message)and disablesbit-stuffing,indicatinga bits of the samelogicleveloccurinsuccessionduringnor maloperation,a bit of the oppositelogiclevelisstuffedinto the data. IFS This 7-bitinterframespace(IFS)containsthe time requiredby the controllerto movea correctlyreceivedframeto its properpositionin a = 1 0 1R = 1 0 1 RecessiveRecessiveDominant110 VCANHVCANL1 1- bi tIde nti fi erRTRIDEr 0D L C0 ..8C R CA C Kr 11 8 -bi tIde n tif ierSRRSOFB ytes DataEOFEOFEOFFISA August2002 RevisedMay 2016 SubmitDocumentationFeedbackCopyright 2002 2016,TexasInstrumentsIncorporatedIntrodu ctionto the ControllerAreaNetwork(CAN) ExtendedCAN:29-BitIdentifierAs shownin Figure3, the ExtendedCANmessageis the sameas the Standardmessagewith theadditionof: SRR The substituteremoterequest(SRR)bit replacesthe RTRbit in the standardmessagelocationas a placeholderin the extendedformat.

10 IDE A recessivebit in the identifierextension(IDE)indicatesthat moreidentifierbits 18-bitextensionfollowsIDE. r1 Followingthe RTRand r0 bits, an additionalreservebit has beenincludedaheadof the fundamentalCANcharacteristicshownin Figure4 is the oppositelogicstatebetweenthe bus, and thedriverinputand ,a logic-highis associatedwith a one,and a logic-lowisassociatedwith a zero- but not so on a CANbus. This is why TI CANtransceivershavethe driverinputand receiveroutputpins passivelypulledhigh internally,so that in the absenceof any input,the deviceautomaticallydefaultsto a recessivebus stateon all inputand The InvertedLogicof a CANBusBus accessis event-drivenand two nodestry to occupythe bus simultaneously,accessis implementedwith a nondestructive, the nodewinningarbi