NXP Semiconductors MWCT101 S Series, Reference Manual

Page: 1665 / 1761

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
Rx SMB are 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 are 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 the
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 Rx SMB has the same structure as 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.
Table 49-23. Matching architecture
Structure SMB[RTR] CTRL2[RRS] CTRL2[EAC
EN]
MB[IDE] MB[RTR] MB[ID
1
] MB[CODE]
Mailbox 0 — 0 cmp
2
no_cmp
3
cmp_msk
4
EMPTY or
FULL or
OVERRUN
Mailbox 0 — 1 cmp_msk cmp_msk cmp_msk EMPTY or
FULL or
OVERRUN
Mailbox 1 0 — cmp no_cmp cmp RANSWER
Mailbox 1 1 0 cmp no_cmp cmp_msk EMPTY or
FULL or
OVERRUN
Mailbox 1 1 1 cmp_msk cmp_msk cmp_msk EMPTY or
FULL or
OVERRUN
FIFO
5
— — — cmp_msk cmp_msk cmp_msk —
1. For mailbox structure, If SMB[IDE] is asserted, the ID is 29 bits (ID St ID Extended). If SMB[IDE] is negated, the
ID is only 11 bits (ID Standard). For FIFO structure, the ID depends on IDAM.
2. cmp: Compares the Rx SMB contents with the MB contents regardless the masks.
Chapter 49 FlexCAN
MWCT101xS Series Reference Manual, Rev. 3, 07/2019
NXP Semiconductors 1665