| 摘要 |
PROBLEM TO BE SOLVED: To prevent a voice signal sent from a telephone exchange and sneaked to the telephone exchange due to impedance mismatching of a 4/2-wire conver sion section or a voice signal intruded from a telephone subscriber terminal from being misjudged as a pushbutton signal and to prevent a result of reception of the pushbutton signal from being misjudged as 3-frequency or over. SOLUTION: A detection result of each frequency component of low group frequencies and high group frequencies of a pushbutton signal is logically expressed at a predetermined time interval, the detection results are ANDed for each frequency component for a predetermined period and when the result of ANDing includes low group and high group signal components of the pushbutton signal, the result of ANDing is used for a result of reception of the pushbutton signal. Thus, it is prevented that a voice signal is misjudged as a pushbutton signal and an output of 3-frequency or over is obtained as the result of reception of the pushbutton signal.
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