Digital Data Bus (D2B), function

P82.00-2251-11

Sequence of components, shown here as an example on model 220 with code (819) 6-disk CD changer, with code (810) Sound system, with code (813) Voice control system (VCS [SBS]) and with code (855) TELE AID

1 Wake-up

A2 Radio

A2/6 CD player with changer (in trunk)

A2/13 Sound amplifier

A35/11 Voice control system control unit

A35/17 D2B telephone and TELE AID transmitter/receiver

X11/4 Data link connector

Digital data bus (D2B)

The digital data bus (D2B) is a data transfer system for communication and information components that makes use of optical information transmission. The data transfer is conducted using light pulses, which are sent over fiber optic cables to the connected communication and information components. Audio and command signals are converted to light pulses in the source component and transmitted through the fiber optic cable. In the destination component, the light pulse is converted back into an electrical signal. Because of the high transfer rate involved, the digital data bus (D2B) can transmit audio and command signals simultaneously. The simultaneous transfer of source data and command data over the digital data bus (D2B) enables the amount of wiring required to be reduced. The connected components require 2 lines for the power supply (electrical) and
2 lines (input/output) for the fiber optic cable of the digital data bus (D2B) and one line for the wake-up signal (electrical).

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The fiber optic cables can also be used to simultaneously transfer source data (e.g. music and voice from 2 components), without impairing the information content.

Function sequence using "Play CD" on model 220 as an example

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-disk CD changer. The audio signals from the CD player with changer (in trunk) (A2/6), for vehicles with code (819) 6-disk CD changer, are then sent over the digital data bus (D2B) as source data to the sound amplifier (A2/13), for vehicles with code (810) Sound system. In the destination component, the sound amplifier (A2/13), for vehicles with code (810) Sound system, the source data are then converted to electrical signals and played back as audio.

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Data transfer using fiber optic cables has the following advantages:

 Extremely high data transfer rate

 Prevents tapping and crosstalk

 Low sensitivity to electromagnetic radiation

 Short-circuit resistance

 Potential-free connection of connected components

 No oxidation

 Low weight of fiber optic cable

 Small wiring harness diameter

The digital data bus (D2B) is equipped with an enclosed ring structure. The communication and information components are arranged there within a distributor line (series connection). This arrangement is model-specific and shown as follows in the
model 220 by way of an example:

 Radio (A2)

 CD player with changer (in trunk) (A2/6), with code (819) 6-disk CD changer

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 Sound amplifier (A2/13), with code (810) sound system

 Voice control system control unit (A35/11), with code (813) Voice control system (VCS [SBS])

 D2B telephone and TELE AID transmitter/receiver (A35/17) (with code (855) TELE AID)

The information transfer takes place in one direction only, i.e. the light pulses for the voice control system control unit (A35/11), for vehicles with code (813) Voice control system (SBS), on model 220 pass through all components connected to the ring before arriving at the destination component.

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 recorded by the component with the master function.

A model-specific sequence is stored ex factory. In turn, the storage of the sequence ex factory means: if the radio (A2) from one model series is installed in another model series, then the system test recognizes the different sequence of the components and files an error message in the fault memory.

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An error message is also filed if the radio (A2) in a model series is replaced with various equipment components. Irrespective of the error message, the system goes into an operational status. STAR DIAGNOSIS can be used to subsequently adjust the sequence of the components in the digital data bus (D2B).

 The digital data bus (D2B) can be diagnosed through the data link connector (X11/4), except model 129 and
model 202.

 The digital data bus (D2B) is identical in terms of function in all model series, only the sequence of the connected components is altered depending on the national version and equipment.