Abstract: A circuit for a central control TDM PCM telecommunications exchange with groups of terminals connected to a switching network is disclosed in which the terminal groups which are each connected to the duplicated switching network over TDM lines and which each include a subsidiary switching network and a decentral control unit are assigned to one another in pairs. In preparation for the stand-by substitution of the central switching network and associated central processor, in the two terminal groups, assigned to one another in pairs, the subscriber lines and/or connection lines connected to the first of said terminal groups can be switched-over from the subsidiary switching network of the first terminal group to the subsidiary switching network of the partner terminal group, whereupon the decentral control unit additionally undertakes all the control functions for the decentral control unit of the first terminal group.