38.5.2 Loading Messages into Transmit FIFO

Before loading a message into the FIFO, the application must ensure that the FIFO is not full. There is space in the FIFO if TFNRFNIF (CxFIFOSTAy[0]) is set. Loading a message into a full FIFO can corrupt a message that is being transmitted.

The FIFO user address (CxFIFOUAy) points to the RAM of the next transmit message object where the application needs to store the message. T0 of the transmit message object is loaded first, followed by T1, T2 and so on. The maximum number of data bytes is limited by the configured payload. Only the number of data bytes specified by the DLC have to be loaded.

After the message object is loaded into RAM, the FIFO needs to be incremented by setting the UINC (CxFIFOCONy[8]) bit. Doing so will cause the CAN FD Protocol module to increment the head of the FIFO and update CxFIFOUAy.

Now the message is ready for transmission and the next message can be loaded at the new address.