| 摘要 |
A communication terminal supporting direct dial-in service that can accurately establish polarities of station lines and prevent erroneous operation has a direct dial-in connection function of push-button method, and includes: a polarity determining circuit determining polarities of a pair of station lines; a primary acknowledgement signal transmitting circuit responsive to a reception of a call signal after the polarity determining circuit detected reversal of polarities of the station lines, for transmitting a primary acknowledgement signal to a line; an extension designation signal detecting circuit for detecting, after transmission of the primary acknowledgement signal by the primary acknowledgement signal transmitting circuit, reception of an extension designation signal from an exchange, and a polarity establishing circuit responsive to detection by the extension designation signal detecting circuit of the extension designation signal, for establishing polarities of the pair of station lines determined by the polarity determining circuit.
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