Specifications

Message Objects
10-14
case, the stored message is overwritten with the new data if the overwrite
protection control (OPC) bit is cleared. Otherwise, the next mailboxes are
checked.
Note:
For the mailbox interrupt flag (MIFn) bits in the CAN_IFR register to be set,
the corresponding bits in the CAN_IMR register must be enabled. If “polling”
is desired to complete transmission or reception of messages (as opposed
to interrupts), the following bits must be used:
- For transmission: TAn bits in the TCR register
- For reception: RMPn bits in the RCR register
10.3.6 Handling of Remote Frames
Remote frame handling can only be done with mailboxes 0 to 3; mailboxes 4
and 5 cannot handle remote frames.
Receiving a Remote Request
If a remote request is received (the incoming message has the remote trans-
mission request bit [RTR] = 1), the CAN module compares the identifier to all
identifiers of the mailboxes using the appropriate masks in descending order
starting with the highest mailbox number.
In case of a matching identifier with the message object configured as a trans-
mit mailbox and the auto-answer mode bit (AAM) in the message set, the mes-
sage object is marked to be sent (TRS bit is set). See Figure 10–8 (A).
In case of a matching identifier with the message object configured as a trans-
mit mailbox and the AAM bit not set, the message is not received. See
Figure 10–8 (B).
After finding a matching identifier in a send mailbox, no further compare is
done.
In case of a matching identifier with the message object configured as a re-
ceive mailbox, the message is handled like a data frame and the RMP bit in
the receive control register (RCR) is set. The CPU then has to decide how to
handle the situation. See Figure 10–8 (E).
If the CPU wants to change the data in a message object that is configured as
a remote frame mailbox (AAM bit set), it has to set the mailbox number (MBNR)
in the master control register and the CDR in the master control register first.