| 摘要 |
PURPOSE:To shorten a time required for superposing process of pictures and reduce the quantity of hardware of a bit map display unit by controlling a write controlling section by information stored in a control plane and making it possible to store the second picture directly to a display bit map in relation to the first picture. CONSTITUTION:When rewriting only the content of display of the first picture A, if the color of writing is not equal to the background color, the picture element value of the writing color is inputted directly to a display bit map C, and at the same time, output '1' of a comparator F is written in a control plane D as information WB. In the case where the writing color is equal to the background color, corresponding picture elements on the second picture bit map B are read out and inputted to the display bit map C, and at the same time, output '0' of the comparator F is written in the control plane D as information WB. On the other hand, when rewriting only the content of display of the second picture B, picture element value of the writing color is written in the second picture bit map B. At this time, in case of information at corresponding position of the control plane is WB=0, the gate of a multiplexer E1 of a write controlling section E is opened, and simultaneously. written in the display bit map C.
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