170
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
19.7.4
Stamping message
The capture of the timer value is done in the MOb which receives or sends the frame. All managed MOb are
stamped, the stamping of a received (sent) frame occurs on RxOk (TXOK).
19.8
Error management
19.8.1
Fault confinement
The CAN channel may be in one of the three following states:
Error active (default):
The CAN channel takes part in bus communication and can send an active error frame when the CAN macro
detects an error
Error passive:
The CAN channel cannot send an active error frame. It takes part in bus communication, but when an error is
detected, a passive error frame is sent. Also, after a transmission, an error passive unit will wait before initiating
further transmission
Bus off:
The CAN channel is not allowed to have any influence on the bus
For fault confinement, a transmit error counter (TEC) and a receive error counter (REC) are implemented. BOFF
and ERRP bits give the information of the state of the CAN channel. Setting BOFF to one may generate an
interrupt.
Figure 19-12. Line Error mode.
Note:
More than one REC/TEC change may apply during a given message transfer.
19.8.2
Error types
BERR: Bit error. The bit value which is monitored is different from the bit value sent
Note:
Exceptions:
- Recessive bit sent monitored as dominant bit during the arbitration field and the acknowledge slot
- Detecting a dominant bit during the sending of an error frame
SERR: Stuff error. Detection of more than five consecutive bit with the same polarity
CERR: CRC error (Rx only). The receiver performs a CRC check on every destuffed received message from the
start of frame up to the data field. If this checking does not match with the destuffed CRC field, an CRC error is
set
FERR: Form error. The form error results from one (or more) violations of the fixed form of the following bit
fields:
ERRP = 1
BOFF = 0
Error
active
Error
passive
Bus
off
TEC > 127 or
REC > 127
128 occurrences
of 11 consecutive
recessive bit
Reset
interrupt - BOFFIT
TEC > 255
TEC < 127 and
REC < 127
ERRP = 0
BOFF = 0
ERRP = 0
BOFF = 1