Control circuit for key telephone system

摘要

A key telephone system control circuit includes completely solid-state circuitry for performing all internal logical operations of the circuit and a pair of high current relays for performing the output functions of the control circuit. The solid-state circuitry produces one or more of three different control signals in response to various conditions on a telephone line pair to which a key telephone system is connected and in response to various conditions of the key telephone system. The three control signals control the operation of the two relays to generate all output functions required for the key telephone system. The control circuit includes holding circuitry having a latching device for producing one of the control signals indicative of the holding status of the line pair.