Extended Vehicle Network (Evn [Gvn])

Networking
Almost all the control modules of the vehicle are networked over bus systems (CAN, D2B).


This means that:
- There is no direct electrical connection between a sending unit (e.g. a light switch or a temperature sensor) and an executing unit (e.g. a lamp or a fan).
- The wires of the sending units are connected to the nearest control module.
- Input signals are interpreted here to generate a corresponding message which is delivered to the bus system.
- This message is picked up by one or more other control modules.
- These then actuate the respective devices (e.g. lamp or fan). In certain cases. various received messages are also combined in a control module to form a new message. The new message is then also available for other control modules over the bus system.

Essentially three bus systems form the network:
- Engine compartment CAN (CAN C)
- Interior CAN (CAN B)
- Digital databus (D2B)

CAN
CAN stands for "Controller Area Network". It is an electric bus system for carrying data over two wires.

There are two CANs:
- The Interior CAN serving the vehicle's interior systems (power windows, rear window defroster. etc.) and
- The Engine Compartment CAN for the drive and chassis systems.

Higher demands are made on the engine compartment CAN in terms of transmission rate and immunity to interference.

D2B
The D2B (digital databus) is an optical bus system. Data is carried to the network's control modules via fiber optic cables. The following are some of the control modules connected to the D2B:
- The COMMAND operating, display and control module or the radio
- The sound amplifier
- The CD player with changer

Data transfer between bus Systems
- Data are transferred between the engine compartment CAN and the interior CAN via the EIS [EZS] control module (N73) acting as the interface (gateway).
The EIS [EZS] control module (N73) also acts as the interface between the control modules on the interior CAN and the cable to the datalink connector for the STAR Diagnosis tool.
- Data are transferred between the interior CAN and the DZB via the radio or the COMMAND operating, display and control module.


NOTE: Although the instrument cluster (A1) is connected both to the interior CAN as well as to the engine compartment CAN and exchanges data with both systems, it does not ad as an interface (gateway) between the two bus systems!


NOTE: This is the first vehicle in which the restraint systems control module (N217) is also linked to the interior CAN.


NOTE: The internationally standardized network management "OSEK" (open systems and their interfaces for electronics in vehicles) is used for all the control modules on the interior CAN.