| 摘要 |
PURPOSE:To eliminate the need for the conversion of data transmission speed by selecting and using two different frequencies from a frequency region having frequencies sufficiently higher than the clock frequency of digital data for a call and a cut-off signals. CONSTITUTION:A transmission data (a) is inputted from a terminal 11 in the bit timing (b), an NAND circuit 14 is at level ''1'' normally and the data is outputted to an output terminal 22 via a line receiver 21. Turning on a switch 16a or 16b, the polarity of an output of a pulse generator 15 is inverted and the output becomes an output of the circuit 14, an output of an AND circuit 12 goes to a signal (d) being logical product of signals (a) and (c) and the signal goes to an output of the receiver 21. The generator 15 incorporates a 1/2-frequency- division circuit and outputs a pulse train having an f/2 frequency of the call signal in taking the oscillating frequency as (b) (the switch 16b is turned on) and outputs a pulse train having a frequency (f) for the cut-off signal (the switch 16b is turned on) by selecting a selector 19. |
