| 摘要 |
PURPOSE:To attain the stable operation of a host device regardless of the throw-in or the cut-off of the current of an additional unit by supplying the current from the host device and the one which operates the additional unit to a terminal resistor through a backflow prevention diode. CONSTITUTION:When a power source 170 in a host device 100 is turned on, and a power source 270 in a unit 200 is turned off, a diode 255 is set in a forward bias, and a diode 256 is in a reverse bias, therefore, the current is supplied from the power source 170 to a terminal resistor 254. When both power sources 170 and 270 are turned on, the current is supplied to the terminal resistor 254 from the power source having a higher potential. Consequently, by turning on the power source 170 in the host device 100, interface lines 400 and 500 are made effective regardless of the on or off of the power source 270 in the unit 200.
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