Information Bus: Description and Operation

In addition to the Body Computer Module (BCM), an Electronic Control Module (ECM) is used to provide microprocessor control of various engine and emissions related functions. A communications circuit, called the serial data line, has been incorporated to allow the BCM and the ECM to share information to provide additional control capability.

The internal circuitry of each module rapidly switches a circuit between zero and 5 volts, converting information into a series of digitally encoded pulses that represent data. The different control modules read and transmit data on this circuit so that encoded data on the line is simultaneously available to all control modules.