NXP Semiconductors PXN2020, Reference Manual, Page: 711 / 1376

FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 26-97
26.6.5.3.1 Message Buffer Data Field Read Access
For transmit message buffers, the controller will not modify the content of the Message Buffer Data Field.
Thus the application can read back the data at any time without any impact on data consistency.
For receive message buffers the application must lock the related receive message buffer and retrieve the
message buffer header index from the
Message Buffer Index Registers (MBIDXRn) . While the message
buffer is locked, the controller will not update the Message Buffer Data Field.
For receive FIFOs, the application can read the message buffer indicated by the Receive FIFO A Read
Index Register (RFARIR) or the Receive FIFO B Read Index Register (RFBRIR) when the related fill
levels in the Receive FIFO Fill Level and POP Count Register (RFFLPCR) indicate an non-empty FIFO.
26.6.5.3.2 Message Buffer Data Field Write Access
For receive message buffers, receive shadow buffers, and receive FIFOs, the application must not write to
the message buffer data field.
For transmit message buffers, the application must follow the write access restrictions given in
Table 26-92 .
26.6.6 Individual Message Buffer Functional Description
The controller provides three basic types of individual message buffers:
1. Single Transmit Message Buffers
2. Double Transmit Message Buffers
3. Receive Message Buffers
Table 26-92. Frame Data Write Access Constraints
Field single buffered
double buffered
commit side transmit side
DATA, MID, NMV POC:config or MB_DIS
or MB_LCK
POC:config or MB_DIS
or MB_LCK
POC:config or MB_DIS
Table 26-93. Frame Data Field Descriptions
Field Description
DATA 0,
DATA 1,
...
DATA N-1
Message Data — Provides the message data received or to be transmitted.
For receive message buffer and receive FIFOs, this field provides the message data received for this message
buffer.
For transmit message buffers, the field provides the message data to be transmitted.
MID 0,
MID 1
Message Identifier — If the payload preamble bit PPI is set in the message buffer frame header, the MID field
holds the message ID of a dynamic frame located in the message buffer. The receive FIFO filter uses the received
message ID for message ID filtering.
NMV 0,
NMV 1,
...
NMV 11
Network Management Vector — If the payload preamble bit PPI is set in the message buffer frame header, the
network management vector field holds the network management vector of a static frame located in the message
buffer.
Note: The MID and NMV bytes replace the corresponding DATA bytes.