GF54.00-P-0005F CAN Data Bus, Function

GF54.00-P-0005F CAN Data Bus, Function







Task
- Data exchange between individual control units
- Readying sensor signals for several systems
- Reducing the number of electrical lines
- Improving electromagnetic compatibility

Design
The data bus consists of a twisted, two-core data line which connects all the participants together in a parallel circuit. The lines of the data line must not be mixed up (low level or high level). The ME-SFI [ME] control unit (N3/10) (except model 124 and model 140), the DAS [FBS] control unit (N73/1) (model 163), the DAS [FBS] radio frequency/infrared control unit (N54/4) (model 129) and the DAS [FBS] radio frequency control unit (N54/3) (model 170) apply as a terminal with regard to bus adaptation. In each case a terminating resistor of 120 Ohms is installed for this. Exception:ME control unit (N3/10) with engine 120 (each 240 Ohms).

In the case of a resistance measurement of the data line (terminal 15 OFF) the various terminating resistors are connected in parallel in the terminals.

Function
The data are transmitted digitally on the data bus at various intervals. The individual data blocks are defined in a 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.

The sum of the data blocks, the short break between 2 transfer intervals and other properties of the data bus are checked constantly. Any faults detected are stored.

Vehicles with electronic ignition switch control unit (N73)
In the vehicle a distinction is made between a high-speed Controller Area Network bus class C (engine compartment) (CAN-C) and the 6 times slower Controller Area Network bus class B (interior) (CAN-B). The electronic ignition switch control unit (N73) forms the interface (Gateway) for this. This does not apply to vehicles with a central gateway control unit (N93) (except model 203).

Vehicles with central gateway control unit (N93)
The central gateway control unit forms the interface (Gateway) between the two data buses (N93) (except model 203). The central gateway control unit (N93) serves as the interface for STAR DIAGNOSIS for all model series.

The new control unit must be coded again when exchanging a control unit. The control unit can be coded via a menu in the handheld tester (up to 07/99) or via STAR DIAGNOSIS.