CAN Bus

Commonly used in Automobiles

Archive:

• PICList post "CAN and uC"

See also:

• https://www.csselectronics.com/pages/can-bus-simple-intro-tutorial In physical terms, all ECUs are connected on a two-wire bus consisting of a twisted pair: CAN high and CAN low. The wires are often color coded: CAN high is yellow (like the sun), CAN low is green (like the grass). A transceiver connects the wires to the controller, often implemented in an uC aka MCU as part of an ECU (Electronic Control Unit). There are low and high speed variants, as well as FD and XL which further increase speed and payloads.

  There are 4 types of frames, data (set), remote (get), error, overload (rarely used delay). Each frame consists of:

  • SOF: The Start of Frame is a 'dominant 0' to tell the other nodes that a CAN node intends to talk
  • ID: The ID is the frame identifier - lower values have higher priority
  • RTR: The Remote Transmission Request indicates whether a node sends data or requests dedicated data from another node
  • Control: The Control contains the Identifier Extension Bit (IDE) which is a 'dominant 0' for 11-bit. It also contains the 4 bit Data Length Code (DLC) that specifies the length of the data bytes to be transmitted (0 to 8 bytes)
  • Data: The Data contains the data bytes aka payload, which includes CAN signals that can be decoded for information
  • CRC: The Cyclic Redundancy Check is used to ensure data integrity
  • ACK: The ACK slot indicates if the node has acknowledged and received the data correctly
  • EOF: The EOF marks the end of the CAN frame
  Data can be encoded Intel or Motorola. Higher layer protocols like ODBC, ISOBase, CANOpen, etc... provide more complex systems. A CAN DBC file (CAN database) is a text file that contains information for decoding raw CAN data.+
• http://www.llp.fu-berlin.de/pool/newproj/CAN/ can4linux is a driver supporting 82c200 and 82527 based CAN controllers,
• http://www.circuitcellar.com/pastissues/Index-frame.htm
• http://www.esacademy.com
• http://www.can-cia.org
• http://www.kvaser.se/can/protocol/index.htm

  .