| 摘要 |
PURPOSE:To improve the data processing speed by transferring the saved data to a memory device set on a system bus and then to an external local memory via a local bus interface circuit. CONSTITUTION:A memory area of a local memory LM is divided into a picture drawing area and a stack area. When a PAINT instruction is produced from a microprocessor MPU for change the background color of a line pattern on the LM, the data on the LM is read out and the color data is written. The number of unpainted areas are increased and a large quantity of saved data is produced, in a complicated pattern. Then the capacity of a stack memory SM is limited. When the SM has an overflow, an overflow signal OVF is transmitted to control multiplexers MPX1 and MPX2 via a bus control circuit BUSC and to transfer the saved data stored in the SM to a stack area decided previously with a direct access given to the LM. Then the saved data is read out to a graphic controller GC when the unpainted areas are painted out. Thus it is possible to realize a high-speed and effective transfer of data.
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