Circuit arrangement for telecommunications especially telephone installations that switch through digitally by time division

Claim 1

In a digital telephone exchange with time division multiplex switching having a plurality of terminal units for the connection of subscriber lines and external lines wherein each terminal unit is individually connected with external lines and with a codec, said codec comprising a coder and decoder for the analog to digital and digital to analog conversion of the subscriber signals and wherein the digital switching is performed via a connection coupling network, said coupling network comprising a sending and receiving bus, whereby the coder of each codec has access to said sending bus and the decoder of each codec has access to said receiving bus and the switching within the connection coupling network is performed by switching units controlled by a peripheral and by a central information processing unit, the improvement comprising: a second special coupling network which consists of a sending and a receiving bus; a plurality of receivers such as dialling receivers and tone receivers which are connected via decoders with the sending bus of said second special coupling network; a plurality of senders such as tone senders and announcement senders which are connected via coders with the receiving bus of said second special coupling network; and means for selectively switching the terminal units to the coupling network or to the second special coupling network.