Information Bus

The following block diagram illustrates the parallel connection by which the EKM is linked to the multi-information display (MID), the [1][2]lamp control module (LKM II), and the general module (GM II). A separate instrument cluster data line links the EKM and the instrument cluster.
The I-Bus consists of a single wire, over which information is exchanged. This communication is bidirectional (two-way) and the data are transmitted serially (one after the other), not simultaneously. The process of transmitting organized packages of information in this fashion is known as multiplexing.

Because the I-Bus connects in parallel to the EKM, MID, GM II, and LKM II, if any one of these control units sends a message, the message is received by all of the others. All messages are therefore "addressed" to a particular component, for which the information is intended. All other components will ignore the message, and only the component addressed will respond with the appropriate output.
The use of multiplexing (transmitting several messages on the same wire) has many advantages. The number of wiring connections is reduced. This, in turn, leads to increased reliability of the systems. Further, the expansion of the systems at a later date is facilitated, as only one wire is needed to link additional controlled units.

Note that the diagnostic lines (TxD and RxD) are connected to the EKM. Diagnosis of the general module, [1][2]lamp control module, and multi-information display is via the EKM and the I-Bus. Diagnosis of the instrument cluster is via the EKM and the instrument cluster data line. Diagnostic module software is therefore specific to the E31.