Theres some discussion in the C class forum about the fibre optic bus for the CD etc, theres a good description of the D2B optical bus there at

http://forums.mbworld.org/forums/sho...&threadid=3061

It's worth noting that the D2B bus is used to connect
Head-unit->Phone->VCS->CD-player->Digital-BOSE-Amp

The other interesting bus in the car is CAN, I was going to post about this on that thread, but its better in a central place like the General discussion rather than hidden in an odd thread in the C class forum :-

Basically, CAN bus is a twisted pair bus (one pair, and power/ground), all control systems connected listen, and anyone can transmit. As its twisted pair and the signals are oposite polarity, its very noise immune and if one cable is shorted or broken it still works.

There are two main CAN bus's in the MB, the engine one and the interior one. The engine one runs at a faster speed than the interior one as theres more real-time stuff happening in the engine. The electronic ignition switch (EIS) relays some information between the two busses.

The various switches in the car just send a signal on the can bus, such as "open boot" or "driver window fully down". The appropriate controller (in this case the door control module in the drivers door) picks up the message and does what it is told.

This (a) saves huges amounts of cables (b) means that diagnosis is easier as the control units can log fauls etc etc

Other uses of the CAN bus are things like
When reverse is selected, the gear selector electronics transmits a "reverse selected" message.
The overhead-control-panel picks it up and tells the auto-dimming mirror not to dim
The passenger side door control module picks it up and puts the mirror downward to face the curb if appropriate
A module in the rear of the car turns on the reverse lights
The COMAND picks up the signal and knows the car is in reverse so it can work out where the car is going better

CAN is also used to connect the instrument cluster to the audio stuff so that it can put messages on the cluster display and so the cluster can tell the audio when the steering wheel buttons are pressed.

In the latest SL, theres an additional module that watches the CANbus and logs interesting faults and oddities for the diagnosis machine to see later.

CAN is a defined standard. The meanings of the messages sent on it are up to the user of the CAN, ie the Mercedes designers ...

 

It's worth noting that the D2B bus is used to connect
Head-unit->Phone->VCS->CD-player->Digital-BOSE-Amp

the correct wiring is:

Head-unit->AMP->(CD-player->TEL->VR->ECALL)

never connect the AMP somewhere else, it always should be after the HU.