| 摘要 |
PURPOSE:To avoid a situation which goes to an interference of the data transmission of other subscriber who requests the communication since an unnecessary carrier is sent to an upstream by stopping sending unnecessarily a carrier signal to a center except the data period from a subscriber side. CONSTITUTION:When a subscriber side transmits the data to a center side, the data, which occurs at a CPU25, is added through a decreasing filter 31 to a multiplier 30. To the multiplier 30, an oscillating output from an oscillating device 29 to continue to oscillate only for a transmitting request signal (RST signal) period sent from the CPU25 is added as a carrier, and the modulation to send the data is executed. A carrier sending time setting circuit 28, when the sending of the carrier continues over the RST period, detects the existence of the unnecessary carrier. As the result of the detection, an input side of an inverter 51 goes to be a high level and an output level goes to be a low level and a negative pulse occurs at the resetting terminal of FF. The above- mentioned FF is reset by the negative pulse, the output of the output terminal Q goes to be a low level, a transistor 42, which constitutes the oscillating device 29, is interrupted and the oscillation is stopped.
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