Preface
MPC5565 Microcontroller Reference Manual, Rev. 1.0
21-8
Freescale Semiconductor
c
Table 21-5. Message Buffer Code for RX Buffers
RX Code before
RX New Frame
Description
RX Code after
RX New Frame
Comment
0000
NOT ACTIVE: 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
Section 21.4.3.1, “Matching Process
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.
0XY1
1
1
Note that for TX MBs (refer to
), the BUSY bit should be ignored upon read.
BUSY: FlexCAN is updating the
contents of the MB. The CPU
must not 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 21-6. Message Buffer Code for TX Buffers
RTR
Initial TX
Code
Code after
Successful
Transmission
Description
X
1000
—
INACTIVE: MB does not participate in the arbitration process.
0
1100
1000
Transmit data frame unconditionally once. After transmission, the MB
automatically returns to the INACTIVE state.
1
1100
0100
Transmit remote frame unconditionally once. After transmission, the
MB automatically becomes and RX MB with the same ID.
Summary of Contents for MPC5565
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