| 摘要 |
PURPOSE:To reduce a sudden change in the load of a power supply at the time of refreshing and to prevent the drop of a power supply voltage by executing refreshing operation at periods different every memory unit, e.g. every memory card, obtained by dividing a memory area. CONSTITUTION:Memory cards 11, 21 are connected to a memory bus 1 and each memory card includes a control circuit 12, identification (ID) information 4 and a dynamic RAM 15. The control circuit 12 reads out the ID information 14 immediately after turning on the power supply, sets up an initial value formed in itself in a refresh counter in a refresh control circuit 17 and then actuates the refresh counter. Since different initial values are set up in each ID information of the memory cards 11, 21, refreshing operation can be executed in different periods in each memory unit. Consequently, the drop of the power supply voltage can be prevented at the time of refreshing operation.
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