Freescale Semiconductor MPC5604B, Быстрый старт

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Figure 114 : Arbitration process with the use of dominant/recessive signals
The advantage of using this king of dominant/recessive data is the simplification of arbitration.
As it can be seen on the figure above, the first frame is transferred by the device n°2 where
devices n°1 and n°3 have to wait and acknowledge using a dominant bit while device n°2 is
emitting recessive. Then devices n°1 and n°3 begin transmitting at the same time, but n°3 wins
over n°1 thanks to its address’ priority (thanks to dominance of lower addresses) and device n°1
has to wait the next cycle. It is clear how much the process of arbitration is automatized thanks
to these signals.
1.4. Error detection
There different kind or errors detectable by these networks, most common are:

Bit error: while a device is transmitting, it also reads back the bus to check the logic
value on the bus is consistent with what is being sent. If it reads dominant while sending
recessive, this error occurs. But the error is not raised during arbitration or acknowledge
fields, because it is expected to have different values for these phases.

Stuff error: CAN bus specifies that over 6 bits of the same polarity cannot be transmitted,
therefore CAN controllers automatically add a dummy bit of opposite polarity, if 6 bits of
same polarity happen to be transmitted. If the receiver sees over 6 bits of same polarity
therefore it means a problem has occurred.
 CRC error: If the CRC calculated at the receiver is different from the one in the frame, the
frame was altered and an error is raised.

Acknowledge error: This error is raised of none of the listening devices sends a dominant
bit while the emitter is sending a recessive one.
 Form error: If an illegal bit is detected, mismatching CAN protocol’s frame structure.
There are transmitter and receiver error counters that are incremented by a certain value,
depending on error’s gravity, and then decremented at each successful exchange. The current
value of the counter gives an idea of error frequency and can be used as an indicator to halt or
slow down the system if it gets too high.