PXN20RM Datasheet, PDF (720/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

FlexRay Communication Controller (FlexRAY)
SA
HLck
HLckCCSa
MT ^start
MT ^start
search[s+1]
slot s
STS
HLckCCNf
null frame transmit
slot s+1
SSS
HLck
MT ^start
slot s+2
Figure 26-124. Null Frame Transmission from HLck state
If a transmit message buffer is in the CCSa or HLckCCSa state at the start of the transmission slot, a null
frame is transmitted in any case, even if the message buffer is unlocked or committed before the
transmission slot starts. A transmit message buffer timing and state change diagram for null frame
transmission for this case is given in Figure 26-125.
SA
HU
HLck
HLckCCSa
MT ^start
MT ^start
search[s+1]
slot s
CCSa
STS
CCNf
null frame transmit
slot s+1
SSS
Idle
MT ^start
slot s+2
Figure 26-125. Null Frame Transmission from HLck state with unlock
Since the null frame transmission will not use the message buffer data, the application can lock/unlock the
message buffer during null frame transmission. A transmit message buffer timing and state change
diagram for null frame transmission for this case is given in Figure 26-126.
Idle
SA
MT ^start
MT ^start
search[s+1]
CCSa
slot s
STS
HL
CCNf
HLckCCNf
null frame transmit
slot s+1
SSS
HLck
MT ^start
slot s+2
Figure 26-126. Null Frame Transmission from Idle state with locking
26.6.6.2.7 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 controller updates the slot status field of the message
26-106
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor