Apparatus and method for determining the state of a telephone line
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United States of America Patent
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Aug 18, 1992
Grant Date -
N/A
app pub date -
Oct 2, 1990
filing date -
Oct 2, 1990
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A line state detector for a telephone line tests a voltage derived from the telephone line by closing a switch in series with a voltage sensing circuit in response to a polling signal. A modem testing the line state go Off-Hook immediately after it finds that the line was in On-Hook state, so it can use a low impedance voltage sensor directly on the telephone line. Monitoring equipment will need a line state detector with high impedance, which can be achieved by a high impedance in series with a capacitor. The capacitor voltage can then be tested by a low impedance sensing circuit.
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