Patent ID: 6157713
Filing Date: 2000-12-05
Classification: H04M

Abstract:
A hold circuit for a telephone coupled to an external telephone, the hold circuit comprising:an input control terminal;a tri-state input device, coupled to the input control terminal, configured and arranged to (A) receive an extension release signal from the external telephone and (B) provide a tri-state signal to the input control terminal, said tri-state signal having one among a hold status, a release status, and a floating status;a power supply, coupled to the input control terminal, configured and arranged to provide a high impedance signal to the input control terminal for preventing the extension release signal from causing said tri-state signal to have the release status;a hold button circuit, coupled to the input control terminal, configured and arranged to produce a hold activation signal at least in part in response to the hold status and regardless of an on-hook state of the telephone; anda detecting circuit, coupled to the input control terminal and the hold button circuit, configured and arranged to provide a high impedance detection signal at least in part in response to the hold activation signal, said high impedance detection signal having alternating high and low levels, andwherein said tri-state signal has the floating status when said tri-state input device does not receive the extension release signal, andwherein an impedance level of the high impedance signal is substantially equal to an impedance level of the extension release signal, andwherein said power supply is further configured and arranged to stop providing the high impedance signal at least in part in response to said high impedance detection signal.