Specifications

Message Objects
10-15 CAN Controller Module
The CPU may then perform the access and clear the CDR to tell the CAN mod-
ule that the access is finished. Until the CDR is cleared, the transmission of this
mailbox is not performed. Since the TRS bit is not affected by the CDR, a pend-
ing transmission is stacked after the CDR is cleared. Thus, the newest data
will be sent.
In order to change the identifier in the mailbox, the message object must be
disabled first (ME bit in the MDER = 0).
Sending a Remote Request
If the CPU wants to request data from another node, it may configure the mes-
sage object as a receive mailbox (only mailboxes 2 and 3) and set the TRS bit.
See Figure 10–8 (F). In this case, the module sends a remote frame request
and receives the data frame in the same mailbox that sent the request. There-
fore, only one mailbox is necessary to do a remote request.
To summarize: A mailbox can be configured in four different ways:
- Transmit mailbox (mailboxes 4 and 5 or 2 and 3 configured as transmit)
can only transmit messages.
- Receive mailbox (mailboxes 0 and 1) can only receive messages.
- Mailboxes 2 and 3 configured as receive mailboxes can transmit a remote
request frame and wait for the corresponding data frame if the TRS bit is
set.
- Mailboxes 2 and 3 configured as transmit mailboxes can transmit a data
frame wherever a remote request frame is received for the corresponding
identifier, if the AAM bit is set.
Note:
After successful transmission of a remote frame, the TRS bit is reset but no
transmit acknowledge (TA) or mailbox interrupt flag is set.