Information Bus: Description and Operation

GF54.00-P-0005CY CAN Data Bus, Function
MODEL 204.0 with ENGINE 272.911 up to Model Year 8
MODEL 204.0 /2 with ENGINE 272.921 up to Model Year 8
MODEL 204.0 /2 with ENGINE 272.947 up to Model Year 8
MODEL 204.0 with ENGINE 272.948 up to Model Year 8
MODEL 204.0 /2 with ENGINE 272.961 up to Model Year 8
MODEL 204.0 with ENGINE 272.971 up to Model Year 8

CAN stands for "Controller Area Network". This is an electrical bus system for carrying data over two wires.
The tasks are:
^ Data exchange between individual control units
^ Readying sensor signals for several systems
^ Reducing the number of electrical lines
^ Improving the electromagnetic compatibility (EMC)
The CAN data bus consists of a special twisted two-core data line that connects all CAN subscribers (control units) in parallel.
The two lines of the data line must not be swapped (low level/high level). The motor electronics (N3/10) control unit is always a consumer with regard to bus adaptation.
A 120 ohms terminating resistor is therefore installed in the motor electronics control unit.
The data are transmitted digitally over the CAN data bus at various intervals. The individual data blocks are defined in a data protocol and it is specified which data are 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 can be made between the fast (500 kbit/s) drive train CAN (CAN C) and chassis CAN (CAN E) and the slower (83.3 kbit/s) interior CAN (CAN B).
In addition there is a diagnosis CAN (CAN D) with a speed of 500 kbit/s for external vehicle diagnosis.
The ME-SFI [ME] control unit serves as an interface (Gateway) between the drive CAN and chassis CAN. The front SAM control unit with fuse and relay module (N10/1) serves as an interface between the interior CAN, chassis CAN and Diagnostic CAN.
The instrument cluster (A1) and the electronic ignition lock control unit (N73) are connected by two CAN data buses and exchange data with both data bus systems. However they do not serve as an interface between both data bus systems
When a control unit is changed the new control unit has to be coded again. This control unit coding is possible via a menu item in the DAS.
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.