| 摘要 |
PURPOSE:To detect a high impedance state in addition to H, L states, by mutually connecting a storage circuit provided with a charging and a storage circuit provided with a discharge circuit and storing information at charging discharging times at external signal input. CONSTITUTION:A signal input terminal I is connected to a signal output terminal of a device to be detected. When an input signal is at an H or L, output terminals n1 and n2 go to the H or L. When an input signal impedance is high, a equivalent capacitance C3 is connected between the input terminal I and ground. At the period of signals S1=S2=H, and S3=S4=L, capacitances C1 and C3 are charged and the input terminal I and the output terminal n1 go to H. At the period of S1=S2=L, S3=S4=H, since the capacitors C1 and C3 keep the charge charged with the previous period, the potential of the input terminal I and output terminal n1 keeps the H. Further, at the period of S1=S2=L and S3=S4=H, the capacitance C1 keeps the charge and the output terminal n1 keeps H state. On the other hand, the capacitances C2 and C3 are discharged and the potential of the input terminal I and the output terminal n2 become the L state. At the period of the signals S1-S3=L and S4=H, the state is unchanged from the previous state. |
