Dedicated Tx Buffers are intended for message transmission under complete control of the processor. Each dedicated Tx Buffer is configured with a specific Message ID. In case that multiple Tx Buffers are configured with the same Message ID, the Tx Buffer with the lowest buffer number is transmitted first.
If the data section has been updated, a transmission is requested by an Add Request via MCAN_TXBAR.ARn. The requested messages arbitrate internally with messages from an optional Tx FIFO or Tx Queue and externally with messages on the CAN bus, and are sent out according to their Message ID.
A dedicated Tx Buffer allocates Element Size 32-bit words in the Message RAM (see the table below). Therefore the start address of a dedicated Tx Buffer in the Message RAM is calculated by adding transmit buffer index (0…31) × Element Size to the Tx Buffer Start Address TXBC.TBSA.
| TXESC.TBDS[2:0] | Data Field [bytes] |
Element Size [RAM words] |
|---|---|---|
| 0 | 8 | 4 |
| 1 | 12 | 5 |
| 2 | 16 | 6 |
| 3 | 20 | 7 |
| 4 | 24 | 8 |
| 5 | 32 | 10 |
| 6 | 48 | 14 |
| 7 | 64 | 18 |