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F28075 CAN controller - updating a transmit object

John Szybist
Intellectual 310 points

Must bits [23:16] of the IF1/IF2 command register be written PRIOR to writing the message object number, bits [7:0] of the same register or can one write all 32 bits of the command register at once? Writing all 32 bits at once seems to make more sense because of 32 bit nature of the CAN controller's registers but the f28075 TRM (SPRUHM9) on page 1987 states:

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.

which seems to imply sequencing to the register 16 bits at a time.

Also, does a user's guide exist for this CAN controller?

  • 0
    TI__Expert 8950 points

    John,


    You can write all of the IF1 and IF2 command register bits at once. In fact, you have to, since only 32-bit accesses to the CAN registers are allowed. The reason for the statement in the TRM is that writing to bits [7:0] is what actually starts the message object transfer. On our Concerto devices, you could write to the different parts of the register separately. I don't think this was particularly common since there's no reason to do so.

    Unfortunately, we do not have a CAN user's guide beyond what's in the TRM.