CAN Data Bus Applications

Currently different bus systems are used for the engine compartment and interior. They differ mainly in transmission rates.

The engine bus has a transmission rate of 125 kbit/sec, the interior bus only has a transmission rate of 83 kbit/sec due to the less time-critical messages.

Data is exchanged between the two bus systems via gateways, control modules which are connected to the two bus systems.

Engine bus
A bus termination, a 120 CE resistance, which is connected between the two cables, is located on each side of the final control module.

The engine bus is only active when the ignition is switched on.

Interior bus
Some control modules on the interior bus are independent of the ignition (e.g. central locking).

Therefore the interior bus must also be available without the ignition, which means it must be possible to transmit data telegrams without the ignition.

However, in order to minimize the quiescent current consumption the bus goes into a "sleep mode" when no data telegrams are transmitted and is only reactivated in the event of a bus access. If a control module (e.g. central locking control module) transmits a message when the CAN bus is in sleep mode, the message is only received by the master (electronic ignition/starter switch). The electronic ignition/starter switch stores the message and transmits a wake-up message to all the control modules on the CAN bus. The electronic ignition/starter switch checks the presence of all participants on the CAN data bus and then transmits the message stored previously.