Abstract: An interface arrangement (2) comprising interface circuits (5,7) and processor (14) allows a personal computer (10) to operate in conjunction with a telephone subset (1) associated with a main switch system (9) in which the signalling systems used by the telephone subset and the computer differ. The interface arrangement allows the subset and the computer to be connected to the subsets switching system to permit at least some of the subsets signalling functions to be performed by the computer.

Abstract: A protection device is provided for a telephone having a two wire subscriber line and an earth line. The protection device comprises a single surge protection device connected between a bridge rectifier polarity guard and the remainder of the telephone circuitry, which is connected to the output of the polarity guard. Three diodes are used to interconnect the earth line and the pair of output lines from the polarity guard to the surge protection device in such a way as to prevent surges from being fed to the remainder of the telephone circuitry. The surge paths including one or two arms of the polarity guard.