For messages to be transmitted dedicated Tx Buffers and/or a Tx FIFO or a Tx Queue can
be initialized or updated. Automated transmission on reception of remote frames is not
implemented.
3.5.1.3 CAN FD Operation
There are two variants in the CAN FD frame transmission, first the CAN FD frame
without bit rate switching. The second variant is the CAN FD frame where control field,
data field, and CRC field are transmitted with a higher bit rate than the beginning and the
end of the frame.
The CAN operation mode is enabled by programming CCCR[CME]. In case
CCCR[CME] = 01 transmission of long CAN FD frames and reception of long and fast
CAN FD frames is enabled. With CCCR[CME] = 10/11 transmission and reception of
long and fast CAN FD frames is enabled. CCCR[CME] can only be changed while
CCCR[INIT] and CCCR[CCE] are both set.
When initialization is left (CCCR[INIT] set to 0), the CAN FD protocol option is
inactive, it has to be requested by writing to CCCR[CMR].
A mode change requested by writing to CCCR[CMR] will be executed next time the
CAN protocol controller FSM reaches idle phase between CAN frames. Upon this event
CCCR[CMR] is reset to 00 and the status flags CCCR[FDBS] and CCCR[FDO] are set
accordingly. In case the requested CAN operation mode is not enabled, the value written
to CCCR[CMR] is retained until it is overwritten by the next mode change request.
Default is CAN operation according to ISO11898-1.
It is not necessary to change the CAN operation mode after system startup. A mode
change during CAN operation is only recommended under the following conditions:
• The failure rate in the CAN FD data phase is significant higher than in the CAN FD
arbitration phase. In this case disable the CAN FD bit rate switching option for
transmissions.
• During system startup all nodes are transmitting according to ISO11898-1 until it is
verified that they are able to communicate in CAN FD format. If this is true, all
nodes switch to CAN FD operation.
• End-of-line programming in case not all nodes are CAN FD capable. Non CAN FD
nodes are held in silent mode until programming has completed. Then all nodes
switch back to CAN communication according ISO11898-1.
When CCCR[CME] is not 00, received CAN FD frames are interpreted according to the
CAN FD Protocol Specification. The reserved bit in CAN frames with 11-bit identifiers
and the first reserved bit in CAN frames with 29-bit identifiers will be decoded as EDL
Chapter 3 Modular CAN (M_CAN)
MPC5777C Reference Manual Addendum, Rev. 1, 12/2015
Freescale Semiconductor, Inc. 89
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