Digital data bus (D2B), function - GF82.00-P-0001A

MODEL 129 as of 1.6.98, 163, 168 as of 1.9.98, 170, 202 as of 1.6.98, 203, 208, 210 as of 1.6.98, 215, 220

Component sequence, exemplified on model 220 with code (819) 6-disc CD changer, with code (810) sound system, with code (813) voice control system (VCS) and with code (855) TELE AID

Fig 1: Identifying Digital Data Bus (D2B), Function

Digital Data Bus (D2B)

The Digital Data Bus (D2B) is a data transmission system for the communication and information components, which utilizes the optical data transfer options. Data transfer is conducted by means of optical pulses, which are transferred over fiber optical cables to the connected communication and information components. Audio and command signals are converted in the source components into optical pulses and transmitted via fiber optical cables. The optical signal is converted back to an electronic signal in the target component. Because of the high transfer rate, the Digital Data Bus (D2B) can transfer audio and command signals simultaneously. Simultaneous transfer of source data and command data over the Digital Data Bus (D2B) significantly reduces the amount of cabling. The connected components require 2 lines for the voltage supply (electrical) and 2 lines (input/output) for the fiber optical cable of the Digital Data Bus (D2B) and one line for the wake-up signal (electrical).

In addition to this the fiber optical cable can transfer several pieces of source data simultaneously (e.g. music and voice from 2 components), without compromising the data content.

Functional sequence on example of "Play CD" on model 220

Pressing "Play" on the radio (A2) sends a command signal over the Digital Data Bus (D2B) to the CD player with changer (in trunk) (A2/6), for vehicles with code (819) 6-disc CD changer. The audio signals from the CD player with changer (in the trunk) (A2/6), for vehicles with code (819) 6-disc CD changer, are then sent over the Digital Data Bus(D2B) as source data to the Sound amplifier (A2/13), or for vehicles with code (810) to the sound system. The target components, the Sound amplifier (A2/13), or for vehicles with code (810) the sound system, the source data are then converted back to electrical signals and reproduced as sound.

Data transfer using fiber optic cables has the following advantages:

Extremely high data transmission rate
Prevents tapping and cross talk
Insensitive to electromagnetic radiation
Short-circuit resistance
Zero potential connection of components
No oxidation
Low weight of fiber optical cable
Minimum diameter of wiring harness

The digital data bus (D2B) has a closed ring structure. The communication and data components are arranged here in a distributor line (in-series circuit). This arrangement is type specific and is illustrated by way of an example on model 220 as follows:

Radio (A2)
CD player with changer (in trunk) (A2/6), with code (819) 6-disc CD changer
Sound amplifier (A2/13), with code (810) Sound System
Voice control system control unit (A35/11), with code (813) voice control system (VCS)
Telephone and TELE AID transmitter/receiver, D2B (A35/17), with code (855) TELE AID

Data transfer is conducted here in one direction only, i.e. the optical pulses for the voice control system control unit (A35/11), for vehicles with code (813) voice control system (VCS), on model 220 pass through all components connected to the ring, before arriving at the target components.

When the system is first put into operation, a system test is performed. In doing so the individual components and their sequence in the ring structure of the Digital Data Bus (D2B) are registered by the component with the master function.

A type-specific sequence is stored ex-factory. In turn, the storing of a sequence ex-factory means: if the radio (A2) is taken from one model series and installed into another one, then during a system test the different sequence of the components and an error message are filed in the diagnostic trouble code memory.

An error message is also filed if the radio (A2) is exchanged within a model series with different equipment components. The system goes to the operational state regardless of the error message. STAR DIAGNOSIS enables the sequence of the components to be subsequently altered in the Digital Data Bus (D2B).

The Digital Data Bus (D2B) is diagnosis capable via the data link connector (X11/4), except for models 129 and 202.

The operating principle of the Digital Data Bus (D2B) is the same for all model series; all that changes is the sequence of components depending on the national version and equipment specification.

Data transfer, function

GF82.00-P-2000A