CAN data bus, function - GF54.00-P-0005PE
MODEL 203 with ENGINE 271.921 /940 /946 /948
MODEL 209 with ENGINE 271.940 /955
CAN stands for "C ontroller A rea N etwork". This is an electrical bus system for carrying data over two wires.
The tasks are:
- Data transfer between individual control units
- Readying sensor signals for several systems
- Reducing the number of electric cables
- Improving the electromagnetic compatibility (EMC)
The CAN data bus consists of a special twisted two-core data line that connects all CAN users (control units) in parallel.
The two lines of the data line must not be mixed up (low level/high level). The ME-SFI [ME] control unit always represents a terminal with regard to bus adaptation.
A 120 Ω terminating resistor is therefore installed in the ME-SFI [ME] control unit.
The data is transmitted digitally over the CAN databus at various intervals. The individual data blocks are defined in a data protocol and it is specified which data is received or transmitted by a control unit.
Each connected control unit is able to transmit or receive data (bidirectional bus).
The sum of the data blocks, the short break between two transmission intervals and additional properties of the CAN data bus are checked constantly. Detected faults are stored and placed in the fault memory.
In the vehicle a distinction is made between a fast (500 kbit/s) engine CAN data bus (CAN-C) for the drive and chassis systems and the slower (83.3 kbit/s) body CAN data bus (CAN-B) for the vehicle interior.
There is also a diagnosis CAN data bus (CAN-D) with a speed of 500 kbit/s for external vehicle diagnosis using STAR DIAGNOSIS.
The interface between the three CAN data buses (gateway) is located in the EIS [EZS] control unit or with model 203 from 04/04 to 11/04 in the central gateway control unit.
The instrument cluster and steering column module are connected both to the body CAN data bus and the engine CAN data bus and exchange data with both data bus systems. But they do not act as an interface (gateway) between both data bus systems.
When a control unit is replaced, the new control unit must be coded again. This control unit coding is possible via a STAR DIAGNOSIS menu.
The international standardized network management "OSEK" (open systems and their interfaces for electronics in motor vehicles) is used for all control units of the CAN data bus.
| ME-SFI [ME] control unit, component description | N3/10 | GF07.61-P-6000KE |