Bus connection

Modern automobiles feature numerous control units for the most diverse purposes (e.g. for ABS, central locking systems, engine management, etc.). As was already described in Chapter 1, development is demanding a continuously increaseing number of networked control units. Initially the control units were connected to each other by numerous individual data lines. However, this type of networking quickly proved to be uneconomical and ineffective, so that the use of bus systems, especially the CAN bus, was necessary.

In this way one control unit can communicate as needed with every other connected control unit using only one bus with two lines.

Every control unit has a bus connection available for this purpose. This consists of a bus controller and a transceiver. The bus controller co-ordinates the transmitting and receiving of data through the bus, so that the CPU is freed from this job and consequently is not additionally loaded. To ensure that the data exchange using one common bus line does not end up in uncontrollable chaos, adherence to certain rules of communication is essential. These rules are established in a protocol. The bus controller makes sure that this protocol is followed. Similar to the signal converter and the output stage, the transceiver sees to it that the signals in the bus are translated into readable signals for the bus controller; and conversely, that only signals that conform to the protocol are sent to the bus. Bus controller and transceiver are normally attached to one part.