| 摘要 |
PURPOSE:To shorten the measuring operation of an interface signal by providing an empty terminal of an external connector, which is connected to a modem, with a terminal for controlling the interface signal and connecting an external switch to said control terminal. CONSTITUTION:Making use of the empty terminal of the external connector connected to the modem 8, polarity inversion control is made with respect to the interface signal (a) transmitted from a modem interface circuit 9, namely, a transmitting data SD, a transmission request signal RS, a timing for transmission synchronizing STI and a data communication speed selecting signal SDS, by short-circuiting and opening an external switch SW. When the external switch is short-circuited while an input terminal connected to an SW terminal of NANDs 14-17 is grounded, respective interface signals output voltage with positive polarity, and when the external switch SW is opened, voltage with negative polarity is outputted. |
