Data Transfer, Function

Data Transfer, Function

Data transfer in the D2B bus
The digital data bus (D2B) has a master unit (radio or COMAND) which can control all components in the D2B system. It also serves as an interface (gateway) to the CAN data bus. For this purpose, signals arriving at the master unit are converted so that they can be transferred from the D2B to the CAN bus and vice versa. Moreover, the master unit serves as a pulsing unit which provides the pulse rate with which the information sections (data frames) are transferred in the bus system. A data frame consists of two subframes. The sequence of many data frames then contains the complete information for malfunction-free operation of the components in the D2B ring (telephone, CD player,...).

Conversion of the light pulses into electrical signals and vice versa is accomplished by the optical transmission and receiving diodes integrated into each 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) and control data ("Play" command for CD player) are transferred.

Source data is transferred synchronously, in the form present on a music CD, for example, as 32-bit blocks in the subframes.

By contrast, control data is transferred asynchronously. It is divided up (2 bits per subframe) and distributed in a number of subframes.

The control data is assigned an address indicating the component in the D2B ring for which the information is intended.

When received by the component, the individual data packages are put back together in the component so that they can be processed. A data frame can therefore contain highly differing information (source and control data for all components present in the D2B ring).

The transmission and receiving diodes as well as the D2B chip are switched off when not required in order to reduce the quiescent current (sleep mode). Switch off if accomplished immediately after the master unit is switched off or after switching off the ignition.

When switched back on, the bus system (transmission and receiving diodes, D2B chip) can be activated either by the components or by the master unit by means of an electrical signal via the wake-up line for transferring information optically.

An edited light signal is fed back into the bus at full intensity regardless of whether the information is intended for the component (repeater function).