FlexCAN
MPC5606S Microcontroller Reference Manual, Rev. 7
674 Freescale Semiconductor
The FlexCAN module stores CAN messages for transmission and reception using a Message Buffer
structure. Each individual MB is formed by 16 bytes mapped on memory as described in Table 18-3.
Table 18-3 shows a Standard/Extended Message Buffer (MB0) memory map, using 16 bytes total space
(0x80–0x8F).
18.3.2 Message Buffer structure
The Message Buffer structure used by the FlexCAN module is represented in Figure 18-2. 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.
Table 18-3. Message Buffer MB0 memory mapping
Address offset MB field
0x80 Control and Status (C/S)
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
S
R
R
ID
E
R
T
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
Figure 18-2. Message Buffer Structure
Table 18-4. Message Buffer Structure field descriptions
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
Tabl e 18-5 and
Tabl e 18-6. See Section 18.4, 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
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