RH850 Series CAN Transmit Procedure (CAN FD Mode)
R01AN6029EJ0100 Rev.1.0 Page
of 42
May 10, 2017
2.5 Transmit Buffer Merge Mode (Only in CAN FD Mode)
Transmit buffers can transmit messages with a payload length of 20 bytes, but can transmit messages with a payload
length of up to 64 bytes by merging three transmit buffers in transmit buffer merge mode.
Setting the TMME bit to 1 in the CmFDCFG register enables transmit buffer merge mode. In this mode,six buffers
per channel become a merge area and two sets of transmit buffers (16 × m) + 0 to (16 × m) + 2 and transmit buffers (16
× m) + 3 to (16 × m) + 5 are merged. A transmission request is made by the first transmit buffer, and subsequent two
buffers are used as a payload storage area.
Set the control register (TMCp register) of the transmit buffer corresponding to the transmit buffer allocated as the
payload storage area to “00H”. Also, set the enable bit of the corresponding interrupt enable register (TMIECy register)
to "0" (interrupt disabled).
While transmit buffer merge mode is enabled, do not link the transmit/receive FIFO buffer to six merged buffers or
allocate it to the transmit queue.
Table 2-1 shows an example of data storage when transmitting 64 bytes in transmit buffer merge mode using transmit
buffer 0.
Table 2-1 Example of Data Storage Using Transmit Buffer 0
Transmit buffer 0 ID data, transmit history data store
enable bit, RTR bit, and IDE bit
Transmit buffer 0 label data and DLC data
Transmit buffer 0 ESI bit, BRS bit, and FDF bit
Transmit buffer 0 data bytes 0, 1, 2, and 3 to transmit
buffer 0 data bytes 16, 17, 18, and 19
Transmit buffer 0 data bytes 20, 21, 22, and 23
Transmit buffer 0 data bytes 24, 25, 26, and 27
Transmit buffer 0 data bytes 28, 29, 30, and 31
Transmit buffer 0 data bytes 32, 33, 34, and 35 to transmit
buffer 0 data bytes 48, 49, 50, and 51
Transmit buffer 0 data bytes 52, 53, 54, and 55
Transmit buffer 0 data bytes 56, 57, 58, and 59
Transmit buffer 0 data bytes 60, 61, 62, and 63
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