BMW F48 - FlexRay Topology and Termination

F48�General�Vehicle�Electronics
1.�Vehicle�Electrical�System
10
Index Explanation
1 Digital�Motor�Electronics�(DME)
2 Electronic�Power�Steering�(electromechanical�power�steering)�(EPS)
3 Dynamic�Stability�Control�(DSC)
4 Body�Domain�Controller�(BDC)
5 Optional�equipment�system�(SAS)
6 Crash�Safety�Module�(ACSM)
FlexRay�data�bus�topology
The�FlexRay�is�shown�in�a�simplified�form�in�the�data�bus�overview.�The�actual�topology�(star-shaped
data�bus�topology)�is�shown�in�the�graphic�at�the�top.
The�star�coupler�with�four�drivers�is�located�in�the�Body�Domain�Controller�(BDC).�The�FlexRay�control
units�are�connected�to�these�bus�drivers�independent�of�their�termination�type.
Bus�termination
As�with�most�bus�systems,�resistors�are�also�used�for�termination�for�the�FlexRay�to�avoid�reflections
on�the�data�lines�at�both�ends�of�the�data�lines.�The�value�of�these�terminating�resistors�is�calculated
from�the�data�transfer�speed�and�the�cable�lengths.�The�terminating�resistors�are�located�in�the�control
units.�In�the�F48�the�terminating�resistors�have�a�value�of�90ohm�(total�resistance�45ohm).
Use�the�vehicle�wiring�diagram�for�measuring�the�(de-energized)�FlexRay�data�bus�for�the
determination�of�the�line�or�terminating�resistor.
Signal�properties
Electrical�faults,�which�arise�from�incorrect�cable�routing,�contact�resistances,�etc.�may�cause�faulty
data�transfer.