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Telephone terminal device with means for detecting abandonment of call

  • US 5,521,975 A
  • Filed: 08/11/1994
  • Issued: 05/28/1996
  • Est. Priority Date: 08/13/1993
  • Status: Expired due to Fees
First Claim
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1. In a telephone system wherein ringing signals cause a change in a polarity of a telephone line, a telephone terminal device with means for detecting abandonment of a call, said telephone terminal device comprising:

  • storage means for storing a value indicating polarity of a telephone line prior to reception of a ringing signal on said telephone line;

    ringing signal detecting means for detecting ringing signals;

    means for activating said telephone terminal device when a predetermined number of said ringing signals are counted;

    means for comparing polarity stored in said storage means with polarity of said telephone line during silent portions of said ringing signals or polarity of said telephone line at time of abandonment of said ringing signals, said silent portions and said abandonment occurring prior to activation of said telephone terminal device; and

    means for restoring said telephone terminal device to standby condition when said compared polarities coincide.

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