Abstract: A circuit arrangement is provided for digital telephone stations in a digital private branch exchange, whereby control information are constantly exchanged via a subscriber line. The telephone station is controlled by a constantly interrogating and controlling microprocessor. The microprocessor can, for example, be arrested by a disturbing pulse. The invention provides the creation of a simple possibility of providing a reset pulse in an out-of-order case of the microprocessor. This is achieved in that repeated actuation of the cradle switch contact in brief succession charges the capacitor, due to multiple charging surges, the reaches the threshold voltage at the base of the transistor that is needed for this transistor, whereby the transistor is activated and generates the reset pulse.

Abstract: For displaying switching states and/or operating states, control switch-luminescent diode combinations are connected at intersections of row drive lines and column drive lines so that application of appropriate potentials to the drive line cause selective energization of the luminescent diodes. A plurality of controllable semiconductor switches are connected to be driven by the column drive lines and are connected to shunt those control switch-luminescent diode combinations which are not to be activated. A current limiting circuit is connected between the luminescent diodes and a supply voltage and is operable from a low ohmic state to a high ohmic state in response to switch-through of all of the controllable semiconductor switches.