| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To enable polarity inversion of a telephone circuit in a section insulated in direct current from the telephone circuit to be detected while at least the telephone circuit is closed of connection, without incurring increase in size and cost. <P>SOLUTION: In a circuit I/F section 17, followings are included: a voltage divider circuit consisting of a diode D1, a resistor R11 and a resistor R22 in order to detect a first telephone line voltage Va on one side of telephone line voltages Va and Vb; and a telephone line voltage detection circuit consisting of a Zener diode D2. It is by this telephone voltage detection circuit that the first telephone line voltage Va is divided before being input to the IO terminal of a DAA 31 (as IO voltage V_POL). The IO voltage V_POL is input to a modem 18 via a transformer 127. The modem 18 detects level inversion of the IO voltage V_POL which was input from the DAA 31, and, if level inversion occurs, notifies that effect to a main CPU 11 to means of an inversion interrupt. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
