the past ten years or so, electronic systems have proliferated in all
aspects of vehicle design, including mechanical systems (engines,
automatic gearboxes, suspension, ABS, etc.), safety systems (airbags,
transponders, etc.) and passenger comfort systems (air conditioning,
radio, etc.). At the same time, a need has developed for on-board
systems to be able to communicate with each other. This has made the
use of multiplex electrics essential.
on a trial basis with the XM in 1994, multiplex electrics were first
applied on the Xsara Picasso. The C5 takes the concept one stage
further with four separate and interdependent networks in which twenty
modules and the built-in systems interface (BSI) are linked by
harnesses referred to as “buses”.
Multiplexing brings the following major advantages :
reliability and simplification of the electrical system, through the
reduction in the number of connecting wires (-30 % compared with an
individually wired system).
Greater user functionality, through permanent dialogue between all the units concerned and the BSI.
built-in systems interface (BSI) controls the entire system through
software running on a microprocessor. This unit centralises incoming
data, decodes it and executes the corresponding orders by sending out
messages in binary format. These messages are coded so that they can
only be read by the unit to which they are addressed. The unit also
provides a bridge between the various networks and transmits diagnostic
information from other units.
addition, the built-in systems interface reduces energy consumption by
running all the multiplexed controller units in low-power mode whenever
possible. The bus carries data between the built-in systems interface
and the other modules in both directions over a single communication
The twenty modules (electronic control units) are interconnected by the following four networks :
Controller Area Network (CAN) carries short messages at high speed
(e.g. engine speed and vehicle speed data for engine, automatic
gearbox, suspension and ABS / ASR modules).
passenger comfort Vehicle Area Network (VAN) transmits long messages at
medium speed for the instrument cluster, display, radio, CD
autochanger, air conditioning system, navigation system and parking
bodywork VAN (consisting of two distinct networks) controls reliable
operation of eight modules : the steering column controls, lighting and
signalling indicators, airbags, left and right electric windows, alarm,
sunroof and particle filter.