SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
If the shift register of the CAN core is ready for loading and if there is no data transfer between the IFx registers and message RAM, the MSGVAL bits in the Message Valid register (DCAN_MSGVAL12 to DCAN_MSGVAL78) and the TXRQST bits in the transmission request register (DCAN_TXRQ12 to DCAN_TXRQ78) are evaluated. The valid message object with the highest priority pending transmission request is loaded into the shift register by the message handler and the transmission is started. The message object’s NewDat bit is reset.
After a successful transmission and if no new data was written to the message object (NewDat = ‘0’) since the start of the transmission, the TxRqst bit will be reset. If TxIE is set, IntPnd will be set after a successful transmission. If the DCAN has lost the arbitration or if an error occurred during the transmission, the message will be retransmitted as soon as the CAN bus is free again. If meanwhile the transmission of a message with higher priority has been requested, the messages will be transmitted in the order of their priority.
If automatic retransmission mode is disabled by setting the DCAN_CTL[5] DAR bit, the behavior of bits TXRQST and NEWDAT in the DCAN_IF1CMD/DCAN_IF2CMD register of the interface register set is as follows:
When a transmission failed (lost arbitration or error), bit NewDat remains set. To restart the transmission, the application has to set TxRqst again.
Received remote frames do not require a receive object. They will automatically trigger the transmission of a data frame, if in the matching transmit object the RmtEn bit is set.