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Chapter 13 FlexRay Communication Controller (FLEXRAY)
MC9S12XF - Family Reference Manual, Rev.1.19
Freescale Semiconductor
549
Figure 13-105. Frame Header Structure
Frame Header Section Access
The frame header is located in the FRM. To ensure data consistency, the application must follow the write
access scheme described below.
For receive message buffers, receive shadow buffers, and receive FIFOs, the application must not write to
the frame header eld.
For transmit message buffers, the application must follow the write access restrictions given in
Table 13-83. This table shows the condition under which the application can write to the frame header entries. In
general, the application can modify all frame header entries when the protocol is in the POC:cong state
or when the message buffer is disabled. For message buffers assigned to the dynamic segment, the
application can modify all frame header entries except the frame ID when the message buffer is locked.
The frame header entries NUF, SYF, SUF, and CYCCNT are not used for frame transmission. These values
are generated internally before frame transmission depending on the current transmission state and
conguration.
For transmit message buffers assigned to the static segment, the PLDLEN value must be equal to the value
message buffer is under transmission. The PE generates a syntactically and semantically correct frame
with payload_length_static payload words and the payload length eld in the frame header set to
payload_length_static.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0x0
R*
PPI
NUF
SYF
SUF
FID
0x2
CYCCNT
PLDLEN
0x4
HDCRC
= not used for TX message buffers, not updated for RX message buffers
Table 13-83. Frame Header Write Access Constraints
Field
TX
Single Buffered
Double Buffered
Static
Segment
Dynamic
Segment
Static Segment
Dynamic Segment
Commit Side
Transmit Side
Commit Side
Transmit Side
FID
POC:cong or MB_DIS
R*, PPI
NUF, SYF
SUF
CYCCNT
PLDLEN
HDCRD
POC:cong
or
MB_DIS
POC:cong
or
MB_DIS
or
MB_LCK
POC:cong
or
MB_DIS
POC:cong
or
MB_DIS
or
MB_LCK
POC:cong
or
MB_DIS