Abstract: A cellular telephone apparatus in which several functions such as decoding and encoding data signals, detecting the busy/idle bit and transponding the SAT signal, are carried out by a CMOS data processor (20) which is separate from a CMOS micro-controller (34). The data processor (20) can be operated at a lower clock frequency (1.2 MHz) than the micro-controller (34) which enables current to be saved compared to processing these functions in software using the micro-controller.

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.