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Modem with power-off ring detection

  • US 4,656,318 A
  • Filed: 05/09/1985
  • Issued: 04/07/1987
  • Est. Priority Date: 05/09/1985
  • Status: Expired due to Term
First Claim
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1. A modem for modulating digital data from a computer for transmission over telephone lines, demodulating data received over the telephone lines for input to the computer, and monitoring the telephone lines to detect an incoming call, using substantially no power from the host computer while monitoring the telephone lines to detect an incoming call, said modem comprising:

  • modulating and demodulating circuits;

    a switchable power supply capable of being remotely switched on and off by a signal from the computer, said switchable power supply, when switched on, drawing power from the computer'"'"'s power source for the modem and, when switched off, drawing substantially no power from the computer'"'"'s power source;

    isolator circuits for coupling the modem to the computer to permit exchange of command and data signals between the computer and the modem, and for preventing power leakage from the computer to the modem when the switchable power supply is switched off;

    a telephone interface circuit for coupling the modulating and demodulating circuits to the telephone lines to permit exchange of data signals between the telephone lines and the modulating and demodulating circuits, said interface circuit including means for isolating the modulating and demodulating circuits from the telephone lines; and

    a ring detector circuit connected to the telephone interface circuit and responsive to the ring signal of an incoming telephone call to produce an output signal for indicating the presence of the incoming call to the computer, said ring detector circuit being operable for detecting incoming calls, but drawing substantially no power from the computer'"'"'s power source, while the switchable power supply is switched off.

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