| 摘要 |
PURPOSE:To prevent a current from flowing to a device whose power source is turned off from a device whose power source is turned on and especially to prevent a useless power consumption of a battery drive device by serially inserting a diode into the pull-up resistance of an interface circuit. CONSTITUTION:The titled circuit is provided with devices A and B and a cable 9. The device B is comprised of an interface receiver 5 with a high input impedance, the pull-up resistance 6 to pull up an input, the diode 7 serially connected to said resistance 6, and a power source 8 connected to the other terminal of the diode 7 through a switch 13. Assuming that only the power source of the device B is cut, the diode 7 prevents the current in an interface equivalent circuit at the time of an insignificant signal from flowing to the device B from the device A. Accordingly the battery of the device A is not uselessly consumed. If only the power source of the device A is cut, the same thing occurs in the device B.
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