Body Control Module: Description and Operation

CCD BUS

The Chrysler Collision Detection multiplex system (CCD Bus) is a twisted pair of wires which travel from module to module receiving and delivering coded information. The code is designed to identify the message it represents as well as the importance of the message. When there are multiple messages attempting to access the CCD bus at one time, the code is used to determine which one has higher priority and is allowed access to the bus first.

The two wires (MX1 and MX2) used by the CCD system are generally called bus + and bus -. Both bus wires have a measurable voltage level of roughly 2.5 volts. In order to maintain the 2.5 volts on each line and provide a means of transportation for the coded messages there must be a voltage divider network consisting of modules with Bias and others with termination. Bias is the part of the voltage divider network which places both bus + and bus - at 2.5 volts. Termination is the circuitry required to complete the voltage divider network and also provide some electromagnetic protection for the bus.