| 摘要 |
<p>PURPOSE:To simplify the hardware by separating a read-out operation from an image memory, from a display operation, and allowing a read-out speed to the image memory in a window boundary part to have a margin. CONSTITUTION:Read of an image data of one raster portion of a CRT display of an image memory 17 is executed by utilizing all one horizontal synchronizing period containing a blanking period asynchronously with a display operation of the display. From the start time of the blanking period, read of the image data of one raster portion on the display is executed. Even in a window boundary part, there is a margin of a time portion of the blanking period with respect to a display operation of the display. Therefore, the contents of the image memory 17 of two pieces or more of window parts can be brought to an access, respectively without changing the read-out period. Also, the window can be superposed by the number of times of an access to the image memory 17 allowed in the blanking period.</p> |
