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Chapter 25 FlexCAN
MPC5606BK Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor
553
25.4.2
Message Buffer Structure
The Message Buffer structure used by the FlexCAN module is represented in
. Both Extended
and Standard Frames (29-bit Identifier and 11-bit Identifier, respectively) used in the CAN specification
(Version 2.0 Part B) are represented.
0x84
Identifier Field
0x88–0x8F
Data Field 0 – Data Field 7 (1 byte each)
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0x0
CODE
SRR
ID
E
RT
R
LENGTH
TIME STAMP
0x4
PRIO
ID (Standard/Extended)
ID (Extended)
0x8
Data Byte 0
Data Byte 1
Data Byte 2
Data Byte 3
0xC
Data Byte 4
Data Byte 5
Data Byte 6
Data Byte 7
= Unimplemented or Reserved
Figure 25-2. Message Buffer Structure
Table 25-4. Message Buffer Structure field description
Field
Description
CODE
Message Buffer Code
This 4-bit field can be accessed (read or write) by the CPU and by the FlexCAN module itself, as part
of the message buffer matching and arbitration process. The encoding is shown in
and
. See
Section 25.5, Functional description
, for additional information.
SRR
Substitute Remote Request
Fixed recessive bit, used only in extended format. It must be set to 1 by the user for transmission (Tx
Buffers) and will be stored with the value received on the CAN bus for Rx receiving buffers. It can be
received as either recessive or dominant. If FlexCAN receives this bit as dominant, then it is
interpreted as arbitration loss.
0 Dominant is not a valid value for transmission in Extended Format frames.
1 Recessive value is compulsory for transmission in Extended Format frames.
IDE
ID Extended Bit
This bit identifies whether the frame format is standard or extended.
0 Frame format is standard.
1 Frame format is extended.
RTR
Remote Transmission Request
This bit is used for requesting transmissions of a data frame. If FlexCAN transmits this bit as 1
(recessive) and receives it as 0 (dominant), it is interpreted as arbitration loss. If this bit is transmitted
as 0 (dominant), then if it is received as 1 (recessive), the FlexCAN module treats it as bit error. If the
value received matches the value transmitted, it is considered as a successful bit transmission.
0 Indicates the current MB has a Data Frame to be transmitted.
1 Indicates the current MB has a Remote Frame to be transmitted.
Note:
Do not configure the last Message Buffer to be the RTR frame.
Table 25-3. Message Buffer MB0 memory mapping
Summary of Contents for MPC5605BK
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