Freescale Semiconductor MCF52277 Reference Manual page 530

FlexCAN
Rx Code
BEFORE
Rx New Frame
0000
0100
0010
0110 was overwritten into a
updating the contents
1
0XY1
The CPU should not try
1
For transmit message buffers (see
Initial Tx
MBn[RTR]
Code
X 1000
0 1100
1 1100
23-20
Table 23-12. Message Buffer Code for Rx Buffers
Description
Rx New Frame
INACTIVE: MB is not
active.
EMPTY: MB is active
and empty.
FULL: MB is full.
OVERRUN: A frame
full buffer.
BUSY: Flexcan is
of the MB with a new
receive frame.
to access the MB.
Table 23-13), the BUSY bit should be ignored upon read.
Table 23-13. Message Buffer Code for Tx Buffers
Code After
Successful
Transmission
—
1000
0100
MCF52277 Reference Manual, Rev. 1
Rx Code
AFTER
MB does not participate in the matching process.
—
MB participates in the matching process. When a
0010 frame is received successfully, the code is
automatically updated to FULL.
The act of reading the control & status (C/S) word
followed by unlocking the MB does not make the
code return to EMPTY. It remains FULL. If a new
0010
frame is written to the MB after the C/S word was
read and the MB was unlocked, the code remains
FULL.
If the MB is FULL and a new frame should be written
into this MB before the CPU had time to read it, the
0110
MB is overwritten, and the code is automatically
updated to OVERRUN.
If the code indicates OVERRUN but the CPU reads
0010 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
0110 another new frame must be written, the MB is
overwritten again, and the code remains OVERRUN.
An EMPTY buffer was written with a new frame (XY
0010
was 01).
A FULL/OVERRUN buffer was overwritten (XY was
11).
0110
INACTIVE: Message buffer not ready for transmit and
participates in the arbitration process.
Data frame to be transmitted once, unconditionally. After
transmission, the MB automatically returns to the INACTIVE
state.
Remote frame to be transmitted unconditionally once, and
message buffer becomes an Rx message buffer with the same
ID for data frames.
Comment
Description
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