| 摘要 |
PURPOSE:To prevent the malfunction of switching control and to decrease the number of times of momentary interruption of a line, by detecting a failure of an input signal at the input side of a modulator/demodulator (modem), and discriminating the switching control so as to attain the discrimination of a failure of the modem. CONSTITUTION:A detecting signal is generated 15 at the modulator side when an input data is unchanged for a prescribed time or over, the detecting signal is generated 2 when an output exceeds a specified level and the detecting signal is generated 3 when an output level continues for a prescribed period or over. Further, the detecting signal is generated 16 at the demodulator side when the input signal exceeds the range of a specified level, the detecting signal is generated 17 when the input signal continues for a prescribed period or over, the detecting signal is generated 8 when a regenerated carrier wave is absent for a prescribed period, the detecting signal is generated 9 when a regenerative clock is absent for a prescribed period or over, and the detecting signal is generated 7 when a demodulated data is unchanged for a prescribed period or over. Further, a switching discriminating circuit 18 discriminates a failure of the modem based on each detecting signal and switches the signal. |
