![](http://datasheet.mmic.net.cn/30000/MC9S12XF512J0VLHR_datasheet_2373534/MC9S12XF512J0VLHR_564.png)
Chapter 13 FlexRay Communication Controller (FLEXRAY)
MC9S12XF - Family Reference Manual, Rev.1.19
564
Freescale Semiconductor
Figure 13-115. Message Transmission Timing
Figure 13-116. Message Transmission from HLck state with unlock
The amount of message data read from the FRM and transferred to the FlexRay bus is determined by the
following three items
1. the message buffer segment that the message buffer is assigned to, as dened by the
Message3. the value of the PLDLEN eld in the message buffer header eld, as described in
If a message buffer is assigned to message buffer segment 1, and PLDLEN > MBSEG1DS, then
2 * MBSEG1DS bytes will be read from the message buffer data eld and zero padding is used for the
remaining bytes for the FlexRay bus transfer. If PLDLEN <= MBSEG1DS, the FlexRay block reads and
transfers 2*PLDLEN bytes. The same holds for segment 2 and MBSEG2DS.
13.6.6.2.6
Null Frame Transmission
A static slot with slot number S is assigned to the FlexRay block for channel A, if at least one transmit
message buffer is congured with the MBFIDRn.FID set to S and MBCCFRn.CHA set to 1. A Null Frame
is transmitted in the static slot S on channel A, if this slot is assigned to the FlexRay block for channel A,
and all transmit message buffers with MBFIDRn.FID = s and MBCCFRn.CHA = 1 are either not
committed, i.e MBCCSRn.CMT = 0, or locked by the application, i.e. MBCCSRn.LCKS = 1, or the cycle
counter lter is enabled and does not match.
Additionally, the application can clear the commit bit of a message buffer that is in the CCMa state, which
is called uncommit or transmit abort. This message buffer will be used for null frame transmission.
the FlexRay block triggers the slot assigned transition SA for up to two transmit message buffers if at least
search[s+1]
MT
start
MA
slot s
TX
SU
CCMa
CCTx
slot s+1
Idle
MT
start
Idle
slot s+2
slot
start
slot
start
slot
start
MT
start
message transmit
SSS
CCSu
search[s+1]
MT
start
MT
start
MA
slot s
TX
SSS
HLckCCMa
CCTx
slot s+1
HLck
MT
start
Idle
slot s+2
slot
start
slot
start
slot
start
HU
CCMa
message transmit