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Wednesday, November 14, 2007

Monday, November 5, 2007

Control Area Networks

CAN Benefits

CAN is low cost:

  • Fast serial bus with two wires: good price/performance ratio
  • Low cost protocol devices (controllers,transceivers) available mainly driven by high volume production in the automotive market.
CAN is reliable:

  • Sophisticated error detection and error handling mechanisms results in high reliability transmission ex: 500 kbits/s,25% bus load, 2000 hours per year. One undetected error every 1000 years.
  • Erroneous messages are detected and repeated.
  • System-wide data consistency (every bus node is informed about an error)
  • Faulty nodes automatically withdraw from bus communication
  • High immunity to Electromagnetic Interference.
CAN is real-time:
  • maximum data rate is 1 MBit/s @ 40m bus length (still about 40 kbit/s @ 1000m bus length)
  • Short message length (0 to 8 data bytes / message)(Larger data can be split up into several messages).
  • Low latency between transmission request and actual start of transmission.
  • Bus access handled via CSMA/CD w/ AMP method (message with the highest priority wins arbitration without losing any time).
CAN is Flexible:
  • CAN allows Multi-Master Operation(every CAN node is able to access the bus individually).
  • CAN Nodes can easily be connected / disconnected (i.e. plug & play).
  • Number of nodes not limited by the protocol.
CAN means Multicast / Broadcast Capability:
  • CAN is not node-oriented but message-oriented.
  • Message identifier specifies contents & priority of the message.
  • Messages can be easily sent to multiple / all nodes simultaneously.
  • All nodes simultaneously receive and work on common data.
CAN is standardized:
  • ISO-11898 (high speed applications).
  • ISO-11519-2 (low speed applications).
How it all began...



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