Instrumentation bus (I-bus)

The instrument bus (I-bus) in the E39 is, in thesame 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 informationvia the I-bus, e.g. sensor values orlamp status.

Design and function of the I-bus

The following control units can be connected to the I-bus:

• BM: On-board monitor (with video module)
  
• BMB: On-board monitor operating unit
  
• CDC: Compact disc changer
  
• DSP: Digital sound processor amplifier
  
• IKE: Instrument cluster electronics
  
• IRIS: Integrated radio information system
  
• LCM: Light check-control module, installed as of 9/95
  In the light check-control module, the functions of the light module and of the check control module are combined in one control unit.
  
• MID: Multi-information display
  
• MFL: Multifunction steering wheel
  
• NAV: 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 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 recognised by radio or telephone operation on the steering wheel.

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

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.