Transmit circuit for PBX subscriber - has both universal and selective transfer of signalling data to subscribers

摘要

The transmit circuit has a transmit unit connected to one line in each pair of signalling lines in order to transmit data simultaneously to all subscribers. A selection circuit is connected into each second line in each pair of signalling lines in order to select any one subscriber and to send data solely to that subscriber and no others. The selection circuits add a character to the data block at a given place. This character is evaluated solely at the evaluator at the receive-end of the line concerned. The selection circuit consists of a zener diode shunted by transistor switch. The advantage lies in the few components needed to send signalling data between subscribers.