SPRUHM9H October 2014 – May 2024 TMS320F28075 , TMS320F28075-Q1 , TMS320F28076
The CPU can update the data bytes of a transmit object any time using the IF1 and IF2 interface registers; neither MsgVal nor TxRqst need 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 or IF1/IF2 Data B register must be valid before the content of that register is transferred to the message object. Either the CPU 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 CPU writes the new data bytes.
When only the data bytes are updated, first 0x87 can be written to bits [23:16] of the Command register and then the number of the message object is written to bits [7:0] 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 can 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 21.10.3.
When NewDat is set together with TxRqst, NewDat is reset as soon as the new transmission has started.