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Chapter 13 FlexRay Communication Controller (FLEXRAY)
MC9S12XF - Family Reference Manual, Rev.1.19
540
Freescale Semiconductor
13.6
Functional Description
This section provides a detailed description of the functionality implemented in the FlexRay block.
13.6.1
Message Buffer Concept
The FlexRay block uses a data structure called message buffer to store frame data, conguration, control,
and status data. Each message buffer consists of two parts, the message buffer control data and the physical
message buffer.
The message buffer control data are located in dedicated registers. The structure of the
message buffer control data depends on the message buffer type and is described in
Section 13.6.3,13.6.2
Physical Message Buffer
All FlexRay messages and related frame and slot status information of received frames and of frames to
be transmitted to the FlexRay bus are stored in data structures called physical message buffers. The
physical message buffers are located in the FRM.The structure of a physical message buffer is depicted in
A physical message buffer consists of two elds, the message buffer header eld and the message buffer
data eld
. The message buffer header eld contains the frame header, the data eld offset, and the slot
status
.The message buffer data eld contains the frame data.
The connection between the two elds is established by the data eld offset.
Figure 13-100. Physical Message Buffer Structure
13.6.2.1
Message Buffer Header Field
The message buffer header eld is a contiguous region in the FRM and occupies ten bytes. It contains the
frame header, the data eld offset, and the slot status. Its structure is shown in
Figure 13-100. The physical
start address SADR_MBHF of the message buffer header eld must be 16-bit aligned.
13.6.2.1.1
Frame Header
The frame header occupies the rst six bytes in the message buffer header eld. It contains all FlexRay
Data Field Offset
Frame Data
Message Buffer Header Field
Message Buffer Data Field
Slot Status
Frame Header
SADR_MBDF
SADR_MBHF
System
Memor
y