Patent ID: 8280017
Filing Date: 2012-10-02
Classification: H04M

Abstract:
1. A communication terminal apparatus, comprising: a ring signal detecting section that detects a ring signal that is sent by a line exchange machine on a line; and a hookup detecting section that monitors a line voltage of the line and detects a hookup of an external attachment telephone, wherein the hookup detecting section, includes: a line voltage detecting section that detects the line voltage that is provided to the line; a reference voltage outputting section that outputs a reference voltage in order to judge whether or not the external attachment telephone is hooked up; a threshold value voltage switching section that switches to a first threshold value voltage when the ring signal is detected by the ring signal detecting section, and switches to a second threshold value voltage when shifting to a receiving mode, the first threshold value voltage being higher than the second threshold value voltage; and a voltage comparing section that, when the ring signal is detected by the ring signal detecting section, compares a difference between the reference voltage and the line voltage with the first threshold value voltage, wherein the hookup detecting section detects that the external attachment telephone is hooked up, when the result of the voltage comparing section indicates that said difference is or over the first threshold value voltage.