Motorola ColdFire MCF5281 User Manual
Page 476
FlexCAN
25-6
Freescale Semiconductor
Table 25-2. Common Extended/Standard Format Frames
Field
Description
Time Stamp
Contains a copy of the high byte of the free running timer, which is captured at the beginning of the
identifier field of the frame on the CAN bus.
Code
Refer to
.
Rx Length
Length (in bytes) of the Rx data stored in offset 0x6 through 0xD of the buffer. This field is written by
the FlexCAN module, copied from the data length code (DLC) field of the received frame.
Tx Length
Length (in bytes) of the data to be transmitted, located in offset 0x6 through 0xD of the buffer. This
field is written by the CPU, and is used as the DLC field value. If remote transmission request (RTR))
= 1, the frame is a remote frame and will be transmitted without the data field, regardless of the value
in Tx length.
Data
This field can store up to eight data bytes for a frame. For Rx frames, the data is stored as it is
received from the bus. For Tx frames, the CPU provides the data to be transmitted within the frame.
Reserved
This word entry field (16 bits) should not be accessed by the CPU.
Table 25-3. Message Buffer Codes for Receive Buffers
Rx Code
Before Rx
New Frame
Description
Rx Code
After Rx
New Frame
Comment
0000
NOT ACTIVE — message buffer is not active.
—
—
0100
EMPTY — message buffer is active and empty.
0010
—
0010
FULL — message buffer is full.
0110
If a CPU read occurs before
the new frame, new receive
code is 0010.
0110
OVERRUN — second frame was received into a full
buffer before the CPU read the first one.
0101
1
1
For transmit message buffers, upon read, the BUSY bit should be ignored.
BUSY — message buffer is now being filled with a new
receive frame. This condition will be cleared within 20
cycles.
0010
An empty buffer was filled.
0011
1
0110
A full buffer was filled.
0111
1
0110
An overrun buffer was filled.
Table 25-4. Message Buffer Codes for Transmit Buffers
RTR
Initial Tx Code
Description
Code After
Successful
Transmission
X
1000
Message buffer not ready for transmit.
—
0
1100
Data frame to be transmitted once, unconditionally.
1000
1
1100
Remote frame to be transmitted once, and message buffer
becomes an Rx message buffer for data frames.
0100
0
1010
1
1
When a matching remote request frame is detected, the code for such a message buffer is changed to be 1110.
Data frame to be transmitted only as a response to a remote
frame.
1010
0
1110
Data frame to be transmitted only once, unconditionally, and
then only as a response to remote frame.
1010
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3