basics of CAN

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Mercedes-Benz Research andDevelopment India
Controller Area Network (CAN)
SUKRUTHRAMESH BABU,EE, MBRDI EmbassyCrest, Banglaore,14-August-2015

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Contents
1. Motivation
2. Introduction
3. CAN communication
4. CAN framing
5. CAN busaccess
6. CAN dataprotection
9/10/2015CAN Presentation| Sukruth Ramesh Babu

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Motivation….
 Intensive electronics
 Creatingcommunicationbetweenelectronic unitswouldenhanceautomobilefeaturescompletely.
Engine
Chassis
Music System
Brakes
Lighting System
Battery
Sensors
oors
Windows
Gauges
Climate Control
eters
Engine
Body
Chassis
Music System
Brakes
Lighting System
Battery
Sensors
Doors
Windows
Gauges
Climate Control
Meters
9/10/2015CAN Presentation| Sukruth Ramesh Babu

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9/10/2015CAN Presentation| Sukruth Ramesh Babu

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Introduction
 CAN (Controller Area Network) is a serial communication technology used especially for reliable data exchange between electronic
controlunits(ECUs) in theautomobile.
 OriginallyintroducedbyBoschin 1983.
 PointtoPointwiringisbeing replaced byoneserial busconnecting all controlsystems.
 StandardizedbyISOandSAE.
9/10/2015CAN Presentation| Sukruth Ramesh Babu

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CAN communication
Basicconcepts
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CAN network
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CAN BUS COMMUNICATION PRINCIPLE
DatathataretransmittedfromanyNode,containsMESSAGElabelledwithIDENTIFIER,which isuniquethroughoutthenetwork
 All other nodes receive the message and each performs an acceptance test on the identifier to determine if the message, and thus its
content,isrelevant tothatparticularnode.
Ifthemessage isrelevant, itwill beprocessed;otherwiseitisignored
 Allows integrationof additionalCANnodeswithoutrequiringmodificationof the CANnetwork.
 Themaximumnumberofnodesisnotspecified. Networksarelimited byelectricalloading,upto64 nodesisnormal
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9/10/2015CAN Presentation| Sukruth Ramesh Babu

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CAN bus logic
9/10/2015CAN Presentation| Sukruth Ramesh Babu

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Vehicle Bus Protocol
Protocol Abbreviation Nature
CAN ControlledAreaNetwork
an inexpensivelow-speedserialbus forinterconnectingautomotive components
automotivecomponents
D2B DomesticDigitalBus a high-speedmultimedia interface
FlexRay -
a generalpurposehigh-speedprotocolwithsafety-criticalfeatures
features
I²C Inter-IntegratedCircuit forattachinglow-speedperipherals
KWP2000 KeywordProtocol2000
–a protocolfor automotivediagnosticdevices(runseitheronaseriallineoroverCAN)
seriallineoroverCAN)
LIN
LocalInterconnectNetwork
a verylowcostin-vehiclesub-network
MOST Media OrientedSystemsTransport a high-speedmultimedia interface
SPI SerialPeripheralInterface
forcommunicationwithslowperipheraldevices,whichareaccessedinfrequently

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CAN Bus characteristics
Buslength / Bitratetradeoff
1Mbit/sec 40meters(131 feet)
500Kbit/sec 100meters(328 feet)
250K bit/sec 200meters(656 feet)
125K bit/sec 500meters(1640 feet)
CAN Presentation| Sukruth Ramesh Babu 9/10/2015

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CAN FRAMES
Data Frame–Fortransmitting userdata
Remote Frame–Used forrequesting 'data frame' from any other CAN node
Error Frame–To indicate errors detected during communication
Overload Frame-To introduce delay in the transmission
CANFRAMETYPES
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DATA FRAME
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DATA FRAME (Standard format and Extended Format)
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CAN Presentation| Sukruth Ramesh Babu
• TheDLC(DataLengthCode)communicatesthenumberof payloadbytesto thereceivers
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REMOTE FRAME
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Error Frame
Types oferror: Therearefivetypesoferroraretherein CANandarelistedbelow.And in caseanyone oftheseerroris observed theerror
frameis transmitted.
 Bit error
 Stufferror
 CRCerror
 Form error
 Acknowledgementerror
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BUS ACCESS IN CAN NETWORK
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PRIORITIZATION OF CAN MESSAGES
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CAN data protection
 Reliabledatatransmission.
 BecauseCANis alsousedin verytime andsafetycritical applicationswithinthe motorvehicle, requirementsfordataintegrity are
extremelyhigh.
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NRZ Coding
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BIT STUFFING
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Error detection:
 Bit monitoring : Compares the bit and the bus level
 ACK Check : Checks for the dominant bit
 Stuff Check : Detection of sixth consecutive bit
 Form Check : Compares the bit stream with message format
 Cyclic Redundancy Check: Compares the bit stream with the generator polynomial
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Error Confinement and Error states:
 Active
 Passive
 Bus OFF REC/TEC > 127
REC/TEC < 128
TEC > 255
Reset or Configuration of
128x11 recessive bits
REC: Receiver Error Counter
TEC: Transmit Error Counter
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Thankyou!!
CAN Presentation| Sukruth Ramesh Babu 9/10/2015