Process for digital, bidirectional data transmission

The invention relates to a process for digital, bidirectional data transmission between a processing unit and a position encoder, as based on the transmission of frames of a predetermined bit length, such that each frame is provided with at least an initial bit length for the transmission of data from the processing unit to the position encoder and at least a second bit length for the transmission of data from the position encoder to the processing unit; and such that the frame is provided with a time slot in which data is neither transmitted from the processing unit to the position encoder nor from the position encoder to the processing unit. In the time slot a triggering signal (external sync signal) is transmitted from the processing unit to the position encoder and this triggers the acquisition of position data. In the first bit length, a clock signal for synchronizing the processing unit and the position encoder is transmitted from the processing unit to the position encoder, and after the acquisition of position data triggered by the external sync signal, the acquired position data is transmitted from the position encoder to the processing unit. Between the transmission of two successive external sync signals at least one additional position-data request signal (internal sync signal) is transmitted from the processing unit to the position encoder, and this signal triggers another acquisition of position data, which is followed by the transmission of the acquired position data from the position encoder to the processing unit.