| 摘要 |
A DTMF signal receiving circuit which is capable of freely selecting a frequency of a received dial tone signal. The DTMF signal receiving circuit receives a DTMF signal, decodes the DTMF signal, and outputs the signal as the decoding result. The DTMF signal receiving circuit comprises a dial tone signal detecting circuit for freely selecting a frequency of a dial tone signal which is the object of detection in accordance with a supplied selection signal, and a judging circuit for judging whether or not the signal as the result of detection of the DTMF signal is output on the basis of the output of the dial tone signal detecting circuit.
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