Key telephone system with directly associated station cards and sets

Claim 1

In a telephone system comprising a plurality of station sets, each including a plurality of key buttons, a. a station circuit for each one of the station sets, each station circuit including interface means for transferring data to and receiving data from its associated station set, said interface means including between 2 and 3 pairs of wires connected with the station set, one pair of which is a talk pair, and the remainder of which is or are for power transmission and for transmission of data related to line, status and audible signaling and for control information including switch status, and b. a line circuit for at least one line, each line circuit including means for transmitting control, status and talk information to, and receiving control, status and talk information from, at least one station circuit connected therewith, the line circuit including line logic means to transmit to a station circuit interface means information corresponding to holding or ringing signals, for visual display and audible signaling at the station sets, c. said station circuit including a data multiplexer and encoder for receiving ringing and hold signals transmitted from at least one line logic means, and for converting said signals into composite digital data which is pulse width encoded and modulated, for transmission to said interface means, d. said interface means comprising a common full duplex transmission junction to which said encoder is operatively connected and to which said composite data is supplied in modulated form, there being a DC power source connected to said junction and said junction connected to said station sets via a remaining wire pair, and e. each station set including circuitry comprising a demodulator to receive and demodulate the modulated composite data, a data separator connected with the output of the demodulator to separate information data from clock data, decoder means responsive to the data separator output to drive station set key lights and an audible ringer, the decoder means also driving line select HOLD and HOOK switches to produce corresponding return control data, and the station set including a modulator operatively connected with the data separator to receive return clock data, and with said switches to receive switch status data, the modulator output also connected with said remaining wire pair to transmit return data thereon and to said junction, in full duplex relation, whereby only one system clock is required, f. the station circuit including circuitry connected with said junction to receive said return data, and responsive to a HOLD command in the return data to transmit a HOLD signal to the line circuit.