Key telephone system

Details Key telephone system Key telephone system

1976-02-26

1976-12-14

Claffy, Kathleen H.

179 84A, 179 18FA, H04M 100

Patent

active

RE0290785

ABSTRACT:
A key telephone system is disclosed that includes a clock for generating both flash and wink lamp signals and digital timing signals. The system also includes a plurality of line control circuits, each of which is associated with an individual telephone line and a plurality of key telephone sets, each of which is associated with one or more telephone lines. Thus the key telephone systems includes a plurality of subsystems, each comprising a telephone line and the line circuit and elements of the key telephone sets associated with that telephone line. Each line circuit includes an electronic ringing detector and hold bridge circuit and a magnetic line current sensor. In addition, each line circuit includes several counters, and each counter is activatable to a plurality of states, one of which corresponds to a particular operational mode of the subsystem. A first group of logic gates responds to the occurrence of conditions associated with a particular operational mode (i.e., presence of loop current and absence of A lead current associated with hold mode) by applying the digital timing signals of the clock to one of the counters and/or enabling the counter to be advanced in response to such signals toward the state corresponding to that particular mode. A second group of logic gates respond to the counter reaching the corresponding state, indicating the continuous existence of the associated conditions for a predetermined period of time, by placing the subsystem in the particular mode (i.e., applying the hold bridge to the line and wink lamp signals to the sets).

REFERENCES:
patent: 3420963 (1969-01-01), Abbot et al.
patent: 3484754 (1969-12-01), Sivda
patent: 3604857 (1971-09-01), Opferman
patent: 3715516 (1973-02-01), Ebrahimi
patent: 3716764 (1973-02-01), Mands
patent: 3749848 (1973-07-01), Knollman et al.
patent: 3789147 (1974-01-01), Saito et al.

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