| 摘要 |
<p>PURPOSE:To monitor the four-wire analog circuit at all times. CONSTITUTION:A tone signal is sent from a tone signal generator 201 of a monitoring adapter 2, which is synthesized with data from a modem 25 and sent to a monitored side. A monitored adapter 1 receiving the signal takes out a tone signal with a low-pass filter 103, which is synthesized with the data from a modem 24 and sent to the monitor. The monitor takes out a tone signal with a low-pass filter 206 and a detection circuit 208 checks the state of receiving tone signals. Accordingly, if the frequency of tone signal is kept outside the frequency band of the transmission data, it can be monitored at all times, resulting in improving the reliability of the circuit.</p> |
