![](http://datasheet.mmic.net.cn/30000/MC9S12XF512J0VLHR_datasheet_2373534/MC9S12XF512J0VLHR_566.png)
Chapter 13 FlexRay Communication Controller (FLEXRAY)
MC9S12XF - Family Reference Manual, Rev.1.19
566
Freescale Semiconductor
Figure 13-120. Null Frame Transmission from Idle state with locking
13.6.6.2.7
Message Buffer Status Update
After the end of each slot, the PE generates the slot status vector. Depending on the this status, the
transmitted frame type, and the amount of transmitted data, the message buffer status is updated.
Message Buffer Status Update after Complete Message Transmission
The term complete message transmission refers to the fact that all payload data stored in the message
buffer were send to FlexRay bus. In this case, the FlexRay block updates the slot status eld of the message
buffer and triggers the status updated transition SU. With the SU transition, the FlexRay block sets the
message buffer interrupt ag MBCCSn.MBIF to indicate the successful message transmission.
Depending on the transmission mode ag MBCCFRn.MTM, the FlexRay block changes the commit ag
MBCCSRn.CMT and the valid ag MBCCSRn.DVAL. If the MBCCFRn.MTM ag is negated, the
message buffer is in the event transmission mode. In this case, each committed message is transmitted only
once. The commit ag MBCCSRn.CMT is cleared with the SU transition. If the MBCCFRn.MTM ag is
asserted, the message buffer is in the state transmission mode. In this case, each committed message is
transmitted as long as the application provides new data or locks the message buffers. The FlexRay block
will not clear the MBCCSRn.CMT ag at the end of transmission and will set the valid ag
MBCCSRn.DVAL to indicate that the message will be transmitted again.
Message Buffer Status Update after Incomplete Message Transmission
The term incomplete message transmission refers to the fact that not all payload data that should be
transmitted were send to FlexRay bus. This may be caused by the following regular conditions in the
dynamic segment:
1. The transmission slot starts in a minislot with a minislot number greater than pLatestTx.
2. The transmission slot did not exist in the dynamic segment at all.
Additionally, an incomplete message transmission can be caused by internal communication errors. If
those error occur, the Protocol Engine Communication Failure Interrupt Flag PECF_IF is set in the
In any of these two cases, the status of the message buffer is not changed at all with the SU transition. The
slot status eld is not updated, the status and control ags are not changed, and the interrupt ag is not set.
search[s+1]
MT
start
MT
start
SA
slot s
STS
SSS
slot s+1
Idle
MT
start
HLck
slot s+2
slot
start
slot
start
slot
start
null frame transmit
HL
CCSa
CCNf
HLckCCNf