Instrumentation Bus

Instrumentation bus (I-bus)

The instrumentation bus (I-bus) in the E38 is, in the same way as the diagnosis bus (D-bus), the body bus (K-bus) and the peripheral bus (P-bus), a serial data link between control units.

The connected control units exchange information via the I-bus, e.g. sensor values or lamp status.

Design and function of the I-bus
The following control units can be connected to the I-bus:

VID: On-board monitor (with video module)

BMB: On-board monitor operating unit

CCM: Check-control module (CCM)
installed as separate control unit only up to 9/95.

DSP: Digital sound processor amplifier and control panel

IKE: Instrument cluster electronics

LM: Light module
installed as separate control unit only up to 9/95.

LCM: Light check-control module, installed as of 9/95
The light check-control module features the functions of the light module and of the check-control module in one control unit.

MID: Multi-information display

FID: Multi-information display, rear compartment

MFL: Multifunction steering wheel

NAJ: Navigation, Japan
Distinction:
The Japan navigation system is connected to the I-bus and is therefore included in the I-bus test. However, the Japan navigation system is only installed in Japan vehicles.
The Philips navigation system (NAV) is not connected directly to the I-bus and is addressed via the video module. It is therefore not included in the I-bus test.

PDC: Park distance control

RAD: Radio

TEL: In-car cellular telephone (with eject box)

Identification features of some I-bus control units
The multifunction steering wheel is recognized by radio or telephone operation on the steering wheel.

The park distance control can be identified bythe ultrasonic distance sensors in the bumpers.

The check-control module (CCM) and the light module (LM) are installed as 2 separate control units only up to 9/95. As of 9/95, both control units are combined in the light check-control module (LCM).

Function of the I-bus
The functional principle of the I-bus is comparable to that of a telephone conference circuit. All participants are interconnected via the I-bus. Every participant can both receive as well as transmit messages via the I-bus.

The I-bus is designed as a single-wire bus system, i.e. the I-bus is a wire system which is used to transmit and receive messages.

The high data transfer rate on the I-bus (approx. 10,000 bit/sec) enables distribution of messages between the control units virtually without delay.

Diagnosis with I-bus control units
DIS diagnosis telegrams are sent to the electronic instrument cluster via the diagnosis bus (D-bus). From the electronic instrument cluster (IKE) the diagnosis telegrams are routed to I-bus control units. The response telegrams of the I-bus control units are sent back also via the IKE to the DIS.