Line interface unit retrofit circuit

Details Line interface unit retrofit circuit Line interface unit retrofit circuit

1991-08-15

1994-09-13

Dwyer, James L.

Telephonic communications

Subscriber line or transmission line interface

379386, 370 13, 370 99, 3701101, 328133, H03K 500

Patent

active

053475763

ABSTRACT:
A retrofit circuit for communication one of three conditions from a line interface unit (LIU) to a receiver unit (RU), using only one external connection between the LIU and the RU. The LIU has a detection circuit and two resistors. The RU has a voltage comparator. The detection circuit outputs a first input signal in response to a signal having ESF and no yellow alarm, a second input signal in response to a signal having ESF and yellow alarm, a third input signal in response to a signal having SF with no yellow alarm, and a fourth input signal in response to a signal having SF with yellow alarm. The resistors output to the external connection a first voltage level in response to the first and third input signals, a second voltage level in response to the second and third input signals, and a third voltage level in response to the second and fourth input signals. The voltage comparator outputs a first output signal and a third output signal in response to detecting the first voltage level at the external connection, a second output signal and a third output signal in response to detecting the second voltage level at the external connection, and a second output signal and a fourth output signal in response to detecting the third voltage level at the external connection.

REFERENCES:
patent: 4147941 (1979-04-01), Curtice
patent: 4488295 (1984-12-01), Sharper
patent: 4835422 (1989-05-01), Dike et al.
patent: 4901026 (1990-02-01), Phillips et al.
patent: 5051614 (1991-09-01), Ohta
patent: 5051628 (1991-09-01), Hanna
patent: 5063564 (1991-11-01), Crandall et al.
patent: 5166925 (1992-11-01), Ward

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