Abstract: In an attachment apparatus for a key telephone system of the type which permits a plurality of intercom substations to access a trunk telephone line via a common communication circuit, a novel subset operable switching circuit is disclosed that permits each subset access to said common communication circuit only on an individual one-at-a-time basis. Transistor circuitry is provided to lock out other stations when more than one subset tries to gain access at the same time.

Abstract: An attachment to key telephone system apparatus is disclosed which permits an intercom substation to access a trunk telephone line. This includes an intercom-to-trunk line access unit for coupling telephonic communications between its input and a selected one of a plurality of trunk lines connected to its output. The unit contains a selector, an advancing means and means responsive to at least one dial digit selection type signal at an input for advancing the selector to a trunk line directly or by means of a nonbusy trunk hunting mode of operation. Relay means are provided at a key service unit, responsive to operation of push button switch means at the selected intercom substation, for interrupting the communications circuits between the intercom substation and the intercom circuit in the key service unit and establishing the communication circuits between the intercom substation and the input of the intercom-to-trunk access unit.

Abstract: An attachment to key telephone system apparatus is disclosed which permits an intercom substation to access a trunk telephone line. This includes an intercom-to-trunk line access unit for coupling telephonic communications between its input and a selected one of a plurality of trunk lines connected to its output. The unit contains a selector, an advancing means and means responsive to at least one dial digit selection type signal at an input for advancing the selector to a trunk line directly or by means of a nonbusy trunk hunting mode of operation. Relay means are provided at a key service unit, responsive to operation of push button switch means at the selected intercom substation, for interrupting the communications circuits between the intercom substation and the intercom circuit in the key service unit and establishing the communication circuits between the intercom substation and the input of the intercom-to-trunk access unit.

Abstract: A touch type dial digit selector to rotary type dial digit sender converts touch type dial input information to a rotary type dial output and includes a touch type selector pad having the ten digit selecting push buttons arranged in four rows and three columns and associated row and column switches, an encoder for converting the information represented by the operation of the row and column switches into a four-bit binary code, a storage and pulsing circuit for receiving the digit information, and providing at an output the series of pulses representative of the dialed number. The storage and pulsing circuit includes a strobe input for initiating the registration of the input information by the storage and pulsing circuit. Means responsive to the concurrent operation of at least one row switch and at least one column switch of said touch type selector provide a strobe pulse to said strobe input at the end of a predetermined time interval greater than N seconds.