FlexCAN
30-19
Freescale Semiconductor
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Table 30-12. 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 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.
0110
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.
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 is
overwritten again, and the code remains OVERRUN.
0XY1
1
1
For transmit message buffers (see
), the BUSY bit should be ignored upon read.
BUSY: Flexcan is
updating the contents
of the MB with a new
receive frame.
The CPU should not try
to access the MB.
0010
An EMPTY buffer was written with a new frame (XY
was 01).
0110
A FULL/OVERRUN buffer was overwritten (XY was
11).
Table 30-13. Message Buffer Code for Tx Buffers
MBn[RTR]
Initial Tx
Code
Code After
Successful
Transmission
Description
X
1000
—
INACTIVE: Message buffer not ready for transmit and
participates in the arbitration process.
0
1100
1000
Data frame to be transmitted once, unconditionally. After
transmission, the MB automatically returns to the INACTIVE
state.
1
1100
0100
Remote frame to be transmitted unconditionally once, and
message buffer becomes an Rx message buffer with the same
ID for data frames.
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
