DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

Error, CRC Error, Acknowledge Error, and Stuff Error. A summary of these error checking
methods is provided in Table 3.3.
Bit ErrorEvery transmitting node monitors its own messages as it transmits them
across the bus, checking the bits in each frame for errors. A transmitting node always
reads back the message as it is sending [21 – 22]. The node will detect a Bit Error if it
sends out a dominant bit when it was supposed to transmit a recessive bit, or a recessive
bit when the message called for a dominant bit. Also, if the bit is not part of the
Arbitration Field or Acknowledge Slot, a Bit Error has been detected. At this point, an
Error Frame is generated and the original message is then resent after a proper
intermission time.
Form ErrorThe first bit in every frame must always be a dominant bit. If any node in
the network detects a dominant bit in one of the following four segments of the message:
End-Of-Frame, Interframe Space, Acknowledge Delimiter, or CRC Delimiter, a Form
Error has occurred. An Error Frame is then generated and the original message is then
resent later after a proper intermission time.
CRC ErrorCyclic redundancy checking is a very effective method of looking for errors
in a network by applying a polynomial equation to a block of transmitted data. The
transmitting node calculates a 15-bit CRC value according to the polynomial Gxin Equation 3.1. The CAN bus applies a CRC-15 with a hamming distance of D 6 for
8 byte information data packets. All nodes on the network receive this message, calculate
their own CRC and verify that the CRC values match. If the values do not match, a CRC
59