SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The software may update the data bytes of a transmit object any time via the IF1/IF2 interface registers, neither MSGVAL, nor TXRQST have to be reset before the update.
Even if only a part of the data bytes are to be updated, all four bytes in the corresponding IF1/IF2 Data A register (DCAN_IF1DATA/DCAN_IF2DATA) or IF1/IF2 Data B register (DCAN_IF1DATB/DCAN_IF2DATB) have to be valid before the content of that register is transferred to the message object. Either the software has to write all four bytes into the IF1/IF2 data register or the message object is transferred to the IF1/IF2 data register before the software writes the new data bytes.
When only the data bytes are updated, first 0x87 can be written to bits [23:16] of the IF1/IF2 Command register (DCAN_IF1CMD/DCAN_IF2CMD) and then the number of the message object is written to bits [7:0] MESSAGE_NUMBER of the command register, concurrently updating the data bytes and setting TXRQST with NEWDAT.
To prevent the reset of TxRqst at the end of a transmission that may already be in progress while the data is updated, NewDat has to be set together with TxRqst in event driven CAN communication. For details, see Section 24.10.4.8.3, Transmission of Messages in Event Driven CAN Communication.
When NewDat is set together with TxRqst, NewDat will be reset as soon as the new transmission has started.