FlexCAN RM0046
538/936 Doc ID 16912 Rev 5
PRIO
Local priority
This 3-bit field is only used when LPRIO_EN bit is set in MCR and it only makes sense for Tx
buffers. These bits are not transmitted. They are appended to the regular ID to define the
transmission priority. See Section 22.4.3, “Arbitration process.
ID
Frame Identifier
In Standard Frame format, only the 11 most significant bits (3 to 13) are used for frame
identification in both receive and transmit cases. The 18 least significant bits are ignored. In
Extended Frame format, all bits are used for frame identification in both receive and transmit
cases.
DATA
Data Field
As many as 8 bytes can be used for a data frame. For Rx frames, the data is stored as it is
received from the CAN bus. For Tx frames, the CPU prepares the data field to be transmitted
within the frame.
Table 267. Message Buffer structure field description (continued)
Field Description
Table 268. Message buffer code for Rx buffers
Rx Code
BEFORE
Rx New Frame
Description
Rx Code
AFTER
Rx New Frame
Comment
0000 INACTIVE: MB is not active. –
MB does not participate in the matching
process.
0100
EMPTY: MB is active and
empty.
0010
MB participates in the matching process.
When a frame is received successfully, the
code is automatically updated to FULL.
0010 FULL: MB is full.
0010
The act of reading the C/S word followed by
unlocking the MB does not make the code
return to EMPTY. It remains FULL. If a new
frame is written to the MB after the C/S word
was read and the MB was unlocked, the code
still remains FULL.
0110
If the MB is FULL and a new frame is
overwritten to this MB before the CPU had
time to read it, the code is automatically
updated to OVERRUN. Refer to
Section 22.4.5, “Matching process for details
about overrun behavior.
0110
OVERRUN: a frame was
overwritten into a full buffer.
0010
If the code indicates OVERRUN but the CPU
reads the C/S word and then unlocks the MB,
when a new frame is written to the MB the
code returns to FULL.
0110
If the code already indicates OVERRUN, and
yet another new frame must be written, the
MB will be overwritten again, and the code will
remain OVERRUN. Refer to Section 22.4.5,
“Matching process for details about overrun
behavior.
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