C.Anudeep (200601020) A.Ajay (200601205) Team - G
Introduction to CAN How CAN works How Arbitration works on CAN bus Frame Format Time Synchronization and Errors CAN Controller Chips CAN Application Layers References
Serial Network Technology for Embedded Solutions. Originally designed by Bosch Gmbh for automotive industry Network technology established among micro- controllers Well suited for high speed/real time applications. Replaces expensive Dual-port RAM technology CAN chips manufactured by Motorola, Philips, Intel, Infineon, and more 600 million CAN nodes used in 2007
High-integrity serial data communications bus for real-time applications Designed for max. performance & reliability Operates at data rates up to 1 Mbit/sec Uses short messages – 8 bytes per message Excellent error detection and fault confinement capabilities ISO 11898 International standard
1983 Start of Bosch internal project to develop in-vehicle network 1986 Official introduction of the CAN protocol 1987 First CAN controller chips by Intel & Philips 1991 Bosch publishes CAN specification 2.0 1992 CAN in Automation (CiA) established 1992 CAN Application Layer (CAL) protocol by CiA 1992 First automobiles equipped with CAN (Mercedes Benz) 1993 ISO 11898 standard published 1994 First International CAN Conference (iCC) 1994 Allen Bradley introduces DeviceNet 1995 ISO 11898 amendment (extended frame format) 1995 CANopen protocol introduced 2000 Development of time-triggered CAN
CAN is used wherever ver two or more micropr oproces ocessor or units need d to communicat unicate e with each h other. r. Passenger Cars (multiple separate CAN networks) • Trucks & Buses, Construction Vehicles, Agricultural Vehicles • Semiconductor Industry (Wafer Handlers, etc.) • Robotics, Motion Control Applications • Passenger/Cargo Trains (Brake Control, Wagon Communication) • Aircrafts (AC, Seat Adjustment) • Building Technologies (Light & Door Control Systems, Sensors, • etc.) Medical Equipment (X-Ray, CAT scanners, etc.) • Household Utilities (Coffee Machine, Washer, etc.) •
• Multi-Master Bus Access • Message Broadcasting • Message Priority (No Node IDs) • Limited Data Length (0…8 bytes) • 1 Mbit/sec Data Rate • Excellent Error Detection & Fault Confinement
Physical and Data Link Layer implemented in Silicon SW Development Engineer is not involved with writing protocol features Low Cost Implementation Worldwide acceptance (ISO 11898 Standard)
Data a messag sages es transm smitted itted from any node e on a CAN bus do not ot con ontain ain addres esses ses of either her the transmit smittin ing g node, de, or of any y intended ended receiv ivin ing g node de Bit enco codin ding CAN uses Non Return to Zero (NRZ) encoding (with bit- stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.
Main Rules of Bus Arbitration • Bit wise arbitration across the arbitration field. • Dominant Bus Level = 0 • Recessive Bus Level = 1 • Uses Carrier Sense, Multiple Access with Collision Detection (CSMA/CD)
Both formats, Standard and Extended, may co-exist on the same CAN bus. The distinction between both formats is managed by “Identifier Extension Bit (IDE) “
• Node A transmits a message • Nodes B,C and D receive the message • Nodes B and D accept the message, Node C declines
• Node A sends a remote frame (request) • Node B,C and D receive message • Node D accepts, Nodes B,C declines the request
• Node D sends requested message • Nodes A,B,C receive the message • Nodes A,B accept the requested message, Node C declines
Bit Monitoring Partitioning of CAN Bit Time into Four Segments Sync_Seg: Signal edge is expected here. Any deviation will affect Phase Buffer lengths. Prop_Seg: Compensates for signal propagation times within the network. Phase_Seg1/2: Compensate for signal edge phase errors by adjusting their length.
Phase Errors Positive Phase Error if the receiving bit starts after Sync_Seg then it’s a Positive Phase Error Negative Phase Error if the receiving bit starts before Sync_Seg then it’s a Negative Phase Error Compensation of Phase Errors Compensation of Positive Phase Error - Phase_Seg1 time increases Compensation of Negative Phase Error - Phase_Seg2 time decreases
Bit Monitoring every transmitter automatically monitors and compares the actual bit level on the bus with the level that it transmitted. Stuff Error More than 5 Bits of same polarity outside of “bit - stuffed” segment CRC Error The 16-bit CRC contains the checksum of the preceding application data for error detection with a 15-bit checksum and 1- bit delimiter.
Acknowledgement Error The ACK field is two bits long and consists of the acknowledge bit and an acknowledge delimiter bit. Form Error Violation of fixed format Bit fields. If a dominant bit is detected, an error is generated. The bits checked are the SOF, EOF, ACK delimiter, and the CRC delimiter bits. Error Probability In conjunction with all the error checking mechanisms, error probability is 10 to the power -11.
Guarantees proper network operation even in cases where malfunctioning nodes produce continuous error condition CAN error detection can pinpoint to “perpetrator” Distinction between temporary and permanent node failures Identification and removal (self-retirement) of malfunctioning nodes from the bus
CAN Node Error States
Transmit Error A transmitting node sends a faulty message ALL receiving nodes in the network respond with an error frame Through “majority vote” the transmitting node is being flagged as the “perpetrator” Receive Error A transmitting node send a perfectly good message Only ONE node in the network responds with an error frame Through “majority vote” the error reporting node is being flagged as the “perpetrator”
Basic CAN One receive, one transmit message FIFO buffer Low cost solution Requires good CPU performance or low CAN data traffic Full CAN Several programmable receive and/or transmit message buffers Most designs also provide Basic CAN features Allows low CPU performance or high CAN data traffic
CAN N and the OSI Model del The CAN specification (ISO11898) discusses only the Physical and Data-Link layers for a CAN network The Data-Link Layer It recognises and understands the format of messages. This layer constructs the messages to be sent to the Physical Layer, and decodes messages received from the Physical Layer . Many applications of CAN require services that are beyond the basic functionality specified by the Data-Link Layer but which may be implemented at the Application Layer. For example, the transmission of data units longer than eight bytes. To meet this need several organisations have developed their own Application Layers.
www.can-cia.org www.softing.com/home/en/industrial- automation/products/can-bus http://en.wikipedia.org/wiki/Controller_Area _Network
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