| 摘要 |
PURPOSE:To ensure an accurate detection for position of a light pen in a detection control system for position of light pen, by producing a dummy mark at the position before a slot of the position detection mark corresponding to the character display region at the left edge on a CRT. CONSTITUTION:A display mark producing circuit 304 produces a light pen position detecting mark M on a display screen 20 by the functions of a slot counter 301 and a low counter 302, and then produces a dummy mark Md at the position before a slot of the mark M at the left edge of the screen 20. When a light pen 10 designates the character display region at the left edge of the screen 20, a part of the mark Md at the left side of the character display region is detected by the pen 10 to stop both the counters 301 and 302. Thus the counters 301 and 302 can be stopped under the same conditions as the normal state, i.e., when the pen 10 designates the areas other than the left edge region and detects a part of the mark M of the region preceding the corresponding region by one to stop the counters 301 and 302. As a result, the position of a light pen can be detected with a high precision. |
