Freescale Semiconductor MCF5329 Reference Manual page 583

Rx Code
BEFORE
Rx New Frame
INACTIVE: MB is not
0000
EMPTY: MB is active
0100
0010
OVERRUN: A frame
0110 was overwritten into a
BUSY: Flexcan is
updating the contents
of the MB with a new
1
0XY1
The CPU should not try
to access the MB.
1
For transmit message buffers (see
Initial Tx
MBn[RTR]
Code
X 1000
0 1100
1 1100
Freescale Semiconductor
Table 23-12. Message Buffer Code for Rx Buffers
Rx Code
Description AFTER
Rx New Frame
—
active.
0010
and empty.
0010
FULL: MB is full.
0110
0010
full buffer.
0110
0010
receive frame.
0110
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
MCF5329 Reference Manual, Rev 3
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 control & status (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 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
MB is overwritten, and the code is automatically
updated to OVERRUN.
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 is
overwritten again, and the code remains OVERRUN.
An EMPTY buffer was written with a new frame (XY
was 01).
A FULL/OVERRUN buffer was overwritten (XY was
11).
Description
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.
FlexCAN
Comment
23-19