Abstract: A PABX cordless telephone system comprising a base station (10) and a plurality of handset (HS1 to HS5). The base station is connected to the public switching network and communicates with each handset by way of a respective duplex radio link. The operation of the PABX system is controlled by a micro-controller (16) in the base station. Micro-controllers are also present in each of the handsets. Security in the radio communication via the duplex radio links is provided by assigning an n-bit security address code, where n for example comprises 16 bits, to each handset. The signalling protocols in setting-up calls require the transmission of the full n-bit security code. In the interim periods the base station (10) carries out a security check on the handsets forming its system.

Abstract: A digital device for controlling a three-phase motor comprises a circuit arrangement for generating three pulse-width modulated carrier waves which are 120.degree. phase-shifted relative to each other, whose modulation depth as a function of time represents a sinewave. A first clock signal periodically starts an up/down counter which counts the second clock signal. The carrier wave is generated by switching a flip-flop each time that the maximum count of the up/down counter is reached and the various modulation pulses which are required are generated symmetrically relative to this maximum count. A sequential network modulates the carrier wave sequentially with the correct modulation pulses.