| 摘要 |
PURPOSE:To detect stably a character position by switching only an area in which a light pen is used from display luminance set by an operator to a fixed luminance display when a light pen is used. CONSTITUTION:A signal indicating an area in which a light pen is used is allotted to plural attribute data of an attribute buffer 2-2 and logical product of the signal, and a switching signal that indicates that the light pen 17 touched on a cathode ray tube 15 is obtained by an AND gate 18, and the output is made to a switching signal of a switching circuit 19. When the light pen is not used, the switching circuit 19 inputs voltage from a variable resistor 16 for adjusting luminance to the grid of the cathode ray tube 15. When the light pen is used, the circuit inputs voltage divided by resistors 20, 21 to the grid of the cathode ray tube 15. Voltage dividing ratio of resistors 20, 21 is made to a value to obtain luminance sufficient to detect the light pen 17.
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