K60P100M100SF2RM Datasheet, PDF (1362/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
5. Clear the Frames Available in Rx FIFO interrupt by writing 1 to IFLAG[BUF5I] bit
(mandatory – releases the MB and allows the CPU to read the next Rx FIFO entry)
48.4.4 Matching Process
The matching process scans the MB memory looking for Rx MBs programmed with the
same ID as the one received from the CAN bus. If the FIFO is enabled, the priority of
scanning can be selected between Mailboxes and FIFO filters. In any case, the matching
starts from the lowest number Message Buffer toward the higher ones. If no match is
found within the first structure then the other is scanned subsequently. In the event that
the FIFO is full, the matching algorithm will always look for a matching MB outside the
FIFO region.
As the frame is being received, it is stored in a hidden auxiliary MB called Rx Serial
Message Buffer (Rx SMB).
The matching process start point depends on the following conditions:
• if the received frame is a remote frame, the start point is the CRC field of the frame;
• if the received frame is a data frame with DLC field equal to zero, the start point is
the CRC field of the frame;
• if the received frame is a data frame with DLC field different than zero, the start
point is the DATA field of the frame;
If a matching ID is found in the FIFO table or in one of the Mailboxes, the contents of the
SMB will be transferred to the FIFO or to the matched Mailbox by the move-in process.
If any CAN protocol error is detected then no match results will be transferred to the
FIFO or to the matched Mailbox at the end of reception.
The matching process scans all matching elements of both Rx FIFO (if enabled) and
active Rx Mailboxes (CODE is EMPTY, FULL, OVERRUN or RANSWER) in search of
a successful comparison with the matching elements of the Rx SMB that is receiving the
frame on the CAN bus. The SMB has the same structure of a Mailbox. The reception
structures (Rx FIFO or Mailboxes) associated with the matching elements that had a
successful comparison are the matched structures. The matching winner is selected at the
end of the scan among those matched structures and depends on conditions described
ahead. See the following table.
1362
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.