| 摘要 |
PURPOSE:To monitor the line connecting state of a remote device, by transmitting and receiving data with the semi-duplex system and transmitting either a carrier or a quasi-carrier at all times. CONSTITUTION:A transmission control signal is turned off at the one-transmission of a data code, a modulator 1 generates a quasi-carrier, and adjusted to a specified level at an attenuator 3 via an LPF2 and transmitted to a line via a hybrid 10. When the transmission control signal is turned on, the carrier is modulated at the modulator 1 in response to the transmission data and a modulation signal is transmitted to the line. |
