| 摘要 |
PURPOSE:To eliminate the need for the conversion of a transmission speed of a digital data by using a pulse train having a frequency sufficiently higher than the clock frequency of the digital data for a call signal and a cut-off signal. CONSTITUTION:A transmission data (a) is inputted from a terminal 11, and since a switch 16 is turned off normally and the level of an NAND circuit 14 is at ''1'', the data is outputted to an output terminal 22 via a line receiver 21. In turning on the switch 16, the polarity of the output of a pulse generator 15 is inverted and the output becomes an output of the circuit 14 and an output of the AND circuit 12 goes to a signal (d) being logical product of signals (a) and (c) and goes to an output of the receiver 21. Since a pulse counter 23 is reset via a differentiating circuit 24 by the pulse train in the timing shown in the signal (b), so far as the output of the receiver 21 remains a digital data shown in the (a), the count value of the counter 23 does not exceed a numerical value ''1''. |
