Chapter 22 FlexCAN
MPC5602P Microcontroller Reference Manual, Rev. 4
540
Freescale Semiconductor
TIME STAMP
Free-Running Counter Time Stamp
This 16-bit field is a copy of the Free-Running Timer, captured for Tx and Rx frames at the time when
the beginning of the Identifier field appears on the CAN bus.
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 22-6. 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
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
for details about overrun
behavior.
Table 22-5. Message Buffer structure field description (continued)
Field
Description