PXR40RM Datasheet, PDF (820/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

FlexCAN Module
Table 24-5. Message Buffer Code for Rx buffers
Rx Code
BEFORE
Rx New Frame
Description
Rx Code
AFTER
Rx New Frame
Comment
0000
0100
0010
INACTIVE: MB is not active.
EMPTY: MB is active and
empty.
FULL: MB is full.
0110
OVERRUN: a frame was
overwritten into a full buffer.
0XY1¹
BUSY: Flexcan is updating the
contents of the MB. The CPU
must not access the MB.
–
0010
0010
0110
0010
0110
0010
0110
MB does not participate in the matching
process.
MB participates in the matching process. When
a frame is received successfully, the code is
automatically updated to FULL.
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.
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 24.4.5, Matching
Process, for details about overrun behavior.
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.
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 24.4.5,
Matching Process, for details about overrun
behavior.
An EMPTY buffer was written with a new frame
(XY was 01).
A FULL/OVERRUN buffer was overwritten (XY
was 11).
NOTES:
1 _{Note that for Tx MBs (see Table 24-6), the BUSY bit should be ignored upon read, except when AEN bit is set}
in the FLEXCAN_x_MCR register.
RTR
X
X
0
Initial Tx
code
1000
1001
1100
Table 24-6. Message Buffer Code for Tx buffers
Code after
successful
transmission
–
–
1000
Description
INACTIVE: MB does not participate in the arbitration process.
ABORT: MB was configured as Tx and CPU aborted the
transmission. This code is only valid when AEN bit in
FLEXCAN_x_MCR is asserted. MB does not participate in the
arbitration process.
Transmit data frame unconditionally once. After transmission, the
MB automatically returns to the INACTIVE state.
24-10
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor