GF54.00-P-0005-04A CAN Data Bus Applications

GF54.00-P-0005-04A CAN Data Bus Applications

Application areas for the CAN data bus
At this time different CAN data bus systems are used for the engine compartment and the passenger compartment. They differ from one another by the rate of transmission.

The CAN engine compartment (CAN C) has a transfer rate of 500 kbit/ sec, the CAN interior (CAN B) has only a transfer rate of 83 kbit/sec on account of less time-critical CAN messages.

Data is exchanged between the two data bus systems via so-called "Gateways", control units which are connected to both.

CAN C/CAN engine compartment
On the last control unit on each side there is a so-called data bus terminator, a resistor with 120 ohms, which is connected between the two lines.
The CAN engine compartment is only active when the ignition is turned on.

CAN B/CAN passenger compartment
Many of the control units that are found in the CAN passenger compartment are not dependent upon the activation of the ignition (for example, central locking).

In this case the CAN passenger compartment has to be accessible with out ignition. This means that it can transmit data telegrams without the ignition being activated.

To keep the resting energy consumption as low as possible the CAN data bus goes into a "sleeping mode" if no data telegrams are being transmitted and is activated again when the data bus is accessed. If when the Controller Area Network interior is "sleeping" a control unit (e.g. on model 202: overhead control panel control unit (N70)) transmits a CAN message, the CAN message is only received by the master (e.g. on model 202: EIS [EZS] control unit (N73)). The respective master control unit stores the CAN message, and transmits a wake-up message) to all control units on the CAN interior. For "wake-up" the control unit (N73) checks the presence of all participants on the CAN data bus and then sends the message stored previously.