CAN Bus Tx/Rx Error Confinement Rules

25. March 2016 04:41 by Christian in
Normal 0 false false false EN-CA X-NONE X-NONE

TEC = Transmitter Error Counter
REC = Receiver Error Counter

  • When a receiver detects an error, the REC will be increased by 1, except when the detected error was a Bit Error during the sending of an Active error Flag or an Overload Flag.
  • When a receiver detects a dominant bit as the first bit after sending an Error Flag, the REC will be increased by 8.
  • When a transmitter sends an Error Flag, the TEC is increased by 8. Exception 1: If the transmitter is Error Passive and detects an ACK Error because of not detecting a dominant ACK and does not detect a dominant bit while sending its Passive Error Flag. Exception 2: If the transmitter sends an Error Flag because a Stuff Error occurred during arbitration, and should have been recessive, and has been sent as recessive but monitored as dominant.
  • If the transmitter detects a Bit Error while sending an Active Error Flag or an Overload Frame, the TEC is increased by 8.
  • If a receiver detects a Bit Error while sending an Active Error Flag or an Overload Flag, the REC is increased by 8.
  • Any node tolerates up to 7 consecutive dominant bits after sending an Active Error Flag, Passive Error Flag or Overload Flag. After detecting the fourteenth consecutive dominant bit (in case of an Active Error Flag or an Overload Flag) or after detecting the eighth consecutive dominant bit following a Passive Error Flag, and after each sequence of additional eight consecutive dominant bits, ever y transmitter increases its TEC by 8 and every receiver increases its REC by 8.
  • After successful transmission of a frame (getting ACK and no error until EOF is finished), the TEC is decreased by 1 unless it was already 0.
  • After the successful reception of a frame (reception without error up to the ACK Slot and the successful sending of the ACK bit), the REC is decreased by 1, if it was between 1 and 127. If the REC was 0, it stays 0, and if it was greater than 127, then it will be set to a value between 119 and 127.
  • A node is Error Passive when the TEC equals or exceeds 128, or when the REC equals or exceeds 128. An error condition letting a node become Error Passive causes the node to send an Active Error Flag.
  • A node is Bus Off when the TEC is greater than or equal to 256.
  • An Error Passive node becomes Error Active again when both the TEC and the REC are less than or equal to 127.
  • A node which is Bus Off is permitted to become Error Active (no longer Bus Off) with its error counters both set to 0 after 128 occurrence of 11 consecutive recessive bits have been monitored on the bus.
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