US 4,057,693 AGranted

Logic control for electronic key telephone line circuit

AssigneeBell Telephone Laboratories, Incorporated

InventorsRonald Joseph Angner, Marion Lee Blount, James Volney Lacy

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Abstract

An electronic key telephone line circuit is disclosed for controlling the hold and disconnect conditions with respect to associated telephone stations in response to transient signals generated upon on-hook to off-hook and off-hook to on-hook transitions of those stations. Due to the nature of the switchhook contacts, the tip and ring leads open before the A-lead opens. Since the disconnect condition is determined from a transient signal caused by the tip and ring lead opening together with an A-lead open, and since by its very nature the transient response of the tip and ring lead transition can be finished before the A-lead opens, timing is used to delay the transient signal to insure that the line circuit goes into the proper mode.

Claims9

Dependent claims

A line circuit for use in a key telephone system for controlling the hold function between a switching machine and at least one telephone station, said line circuit adapted for A-lead control between said line circuit and said station, said hold control circuit comprising

means for providing a momentary station transition signal whenever any of said telephone stations makes a transition from an on-hook to off-hook condition or from an off-hook to an on-hook condition,
means for detecting the presence or absence of a signal on said A-lead,
means for establishing first and second timed intervals where said second timed interval is longer than said first timed interval,
means for recording any provided circuit transition signal for a period of time determined by said established first timed interval,
means for recording a subsequently provided station transition signal for a period of time determined by said established second timed interval,
means controlled jointly by a detected absence of a signal on said A-lead and a recorded provided station transition signal for providing a station disconnect signal,
means for providing a hold bridge enable signal upon a detected absence of a signal on said A-lead and a concurrent absence of a recorded subsequently provided station transition signal, and
means operable during said first timed interval when a provided circuit transition is recorded for reducing said second timed interval to said first timed interval.

5 more elements

A line circuit for use in a key telephone system wherein said line circuit is adapted to control communication connections between a central switching machine and a telephone station and to provide visual signals to said telephone station representative of the circuit state of said line circuit, said line circuit having at least idle, hold and busy states, said line circuit comprising

means for detecting the presence or absence of a digital signal on an A-lead from said telephone station,
means for generating a digital signal in response to signal transitions on the communication leads between said switching machine and said station,
means for detecting the presence or absence of said generated digital communication lead signal,
means for comparing said detected digital A-lead signal with said detected digital communication lead signal, and
a digital timer operative for timing both said digital A-lead signal and said digital communication lead signal,
means controlled by said digital timer for determining which of said communication lead signal transitions are a result of station transitions from the off-hook to the on-hook condition,
means for recording any said determined station transition signal or a first period of time controlled by said digital timer, and
means controlled jointly by said digital timer and said comparing means for enabling said hold state upon a detected absence of said digital A-lead signal and a concurrently recorded absence of said station transition signal.

5 more elements

Dependencies are inferred from the claim text.