Information

• 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.
Table 45-77. 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 Standard + 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 SMB contents with the MB contents regardless the masks.
3. no_cmp: The SMB contents are not compared with the MB contents
4. cmp_msk: Compares the SMB contents with MB contents taking into account the masks.
5. SMB[IDE] and SMB[RTR] are not taken into account when IDAM is type C.
A reception structure is free-to-receive when any of the following conditions is satisfied:
• The CODE field of the Mailbox is EMPTY
Functional description
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
1156
Preliminary
Freescale Semiconductor, Inc.
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