GF82.00-P-2000R Data Transfer, Function

GF82.00-P-2000R Data Transfer, Function

Data transmission in the D2B
The Digital Data Bus (D2B) contains the master unit (radio (A2) or COMAND operating, display and control unit (A40/3)) that can actuate all the components of the D2B system. It acts as an interface (gateway) to the CAN data bus. Signals arriving at the master unit are converted so that they can be transmitted from the D2B to the CAN and vice-versa. Moreover, the master unit serves as a timing circuit which provides the clock pulse with which the information frames are transferred on the bus system. A frame consists of two subframes. A sequence of many data frames then contains the complete information for proper operation of the components in the D2B ring (sound amplifier (A2/13), CD player with changer (A2/6), etc.)

The light pulses are converted into electrical signals and vice- versa by the optical transmit and receive diodes that are integrated into every component.
The electrical signals are then received or transmitted by the D2B chip as D2B protocol in the component.
Source data (music from CD player with changer (A2/6)) and control data ("Play" command with CD player with changer (A2/6)) are transmitted.
Source data are transmitted synchronously in the subframes in 32-bit blocks, like the information on an audio CD.

By contrast, the control data is transferred asynchronously. It is distributed over several subframes (2 bits per subframe).
The control data are provided with the addresses of the components on the D2B ring for which the information is intended. After reception by the component, the individual data packages are recompiled in the component and can then be processed. A data frame can therefore contain many different kinds of information (source data and control data for all the components on the D2B).

The transmit and receive diodes and the D2B chip are switched off if they are not needed in order to reduce the quiescent current (sleep mode). Switch-off is accomplished immediately when the master unit or ignition is switched off. When the system is started up again for optical information transmission, the bus system (transmit and receive diodes, D2B chip) can either be activated by the components or the master unit using an electrical signal on the wake-up line.
Irrespective of whether any information is intended for the component, it puts a prepared optical signal back onto the bus with full intensity (repeater function).