| 摘要 |
PURPOSE:To improve operability by providing a switching circuit that control video signals outputted from a signal outputting circuit stoppably according to presence or absence of horizontal synchronizing signals and monitoring video made by specified video signals when horizontal synchronizing signals are not inputted. CONSTITUTION:A personal computer is connected to an input terminal A by a signal cable. When horizontal synchronizing signals are outputted from the computer, the signals are detected by a diode 1 to obtain DC voltage, and smoothened by a capacitor 2. When a diode 5 is made on by the output through an invertor 4, a signal output circuit 6 becomes low level, and video signals are not inputted to a video circuit 7. On the other hand, when horizontal synchronizing signals are inputted to the terminal A, output of the invertor 4 in a switching control circuit becomes high level the diode 5 is made off. Thereby, specified video signals are inputted from the circuit 6 to the circuit 7, and a video formed by specified video signals is displayed on the display screen.
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