| 摘要 |
PURPOSE:To automatically decide input frequency, by presetting a time within a range consisting of each period of an input signal, and deriving a variation of the signal generated after the preset time, when selecting the input frequency of a time counting device, etc. CONSTITUTION:This device is provided with a waveform shaping circuit 11 for generating a pulse signal P corresponding to frequency of an input signal AC. The signal P is controlled by an AND gate G1 and is supplied to a timing circuit 12. To the circuit 12, a prescribed time within a range consisting of 2 kinds of periods of the signal AC is preset when the signal P is varied. An output signal T of the circuit 12 is supplied to AND gate G2, G3, and to the other input of the gates G2, G3, an output of the gate G1, that is to say, the signal P is supplied. A set signal S of the gates G2, G3 is supplied to FFs 13, 14, respectively, output signals Q1, Q2 are supplied to a time counting device, and also an inverted signal is supplied as a control signal of the gate G1. Also, a reset signal R of the FFs 13, 14 is applied as an initial set signal IR when the electric power supply is turned on. |
