AP29000
Connecting C166 and C500 Microcontroller to CAN
The Controller Area Network (CAN)
Application Note 20 V 1.0, 2004-02
Form Error
If a transmitter detects a dominant bit in one of the four segments End of Frame,
Interframe Space, Acknowledge Delimiter or CRC Delimiter then a Form Error has
occured and an Error Frame is generated. The message is repeated.
Bit Error
A Bit Error occurs if a) a transmitter sends a dominant bit and detects a recessive bit
or b) if it sends a recessive bit and detects a dominant bit when monitoring the actual
bus level and comparing it to the just transmitted bit. In case b) no error occurs during
the Arbitration Field and the Acknowledge Slot.
Stuff Error
If between Start of Frame and CRC Delimiter 6 consecutive bits with the same polarity
are detected, the bit stuffing rule has been violated. A stuff error occurs and an Error
Frame is generated. The message is repeated.
Detected errors are made public to all other nodes via Error Frames. The transmission
of the erroneous message is aborted and the frame is repeated as soon as possible.
Furthermore, each CAN node is in one of the three error states "error active", "error
passive" oder "bus off" according to the value of the internal error counters. The error-
active state is the usual state where the bus node can transmit messages and active
Error Frames (made of dominant bits) without any restrictions. In the error-passive
state, messages and passive Error Frames (made of recessive bits) may be
transmitted. The bus-off state makes it temporarily impossible for the station to
participate in the bus communication. During this state, messages can neither be
received nor transmitted.
3.6 Different CAN Implementations
3.6.1 Standard CAN, Extended CAN
Those Data Frames and Remote Frames, which only contain the 11-bit identifier, are
called Standard Frames according to CAN specification V2.0 part A. With these
frames, 2
11
(=2048) different messages can be identified (identifiers 0-2047). However,
the 16 messages with the lowest priority (2032-2047) are reserved. Extended Frames
according to CAN specification V2.0 part B own a 29-bit identifier. As already
mentioned, this 29-bit identifier is made up of the 11-bit identifier ("Base ID") and the
18-bit Extended Identifier ("ID Extension"). So 2
29
different identifiers are possible.
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