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CHAPTER 21 CAN CONTROLLER
21.5 Transmission of CAN Controller
When 1 is written to TREQx of the transmission request register (TREQR), transmission
by the message buffer (x) starts. At this time, TREQx becomes 1 and TCx of the
transmission complete register (TCR) becomes 0.
■ Starting Transmission of CAN Controller
If RFWTx of the remote frame receiving wait register (RFWTR) is 0, transmission starts immediately. If
RFWTx is 1, transmission starts after waiting until a remote frame is received (RRTRx of the remote
request receiving register (RRTRR) becomes 1).
If a request for transmission is made to more than 1 message buffer (more than one TREQx is 1),
transmission is performed, starting with the lowest-numbered message buffer.
Message transmission to the CAN bus (by the transmit output pin TX) starts when the bus is idle.
If TRTRx of the transmission RTR register (TRTRR) is 0, a data frame is transmitted. If TRTRx is 1, a
remote frame is transmitted.
If the message buffer competes with other CAN controllers on the CAN bus for transmission and
arbitration fails, or if an error occurs during transmission, the message buffer waits until the bus is idle and
repeats retransmission until it is successful.
■ Canceling Transmission Request from CAN Controller
●
Canceling by transmission cancel register (TCANR)
A transmission request for message buffer (x) having not executed transmission during transmission
pending can be canceled by writing 1 to TCANx of the transmission cancel register (TCANR). At
completion of cancellation, TREQx becomes 0.
●
Canceling by storing received message
The message buffer (x) having not executed transmission despite transmission request also performs
reception.
If the message buffer (x) has not executed transmission despite a request for transmission of a data frame
(TRTRx = 0 or TREQx = 1), the transmission request is canceled after storing received data frames passing
through the acceptance filter (TREQx = 0).
Note:
A transmission request is not canceled by storing remote frames (TREQx = 1 remains unchanged).
If the message buffer (x) has not executed transmission despite a request for transmission of a remote frame
(TRTRx = 1 or TREQx = 1), the transmission request is canceled after storing received remote frames
passing through the acceptance filter (TREQx = 0).
Note:
The transmission request is canceled by storing either data frames or remote frames.