Electrical computers and digital processing systems: memory – Storage accessing and control
Reexamination Certificate
1997-10-24
2001-06-19
An, Meng-Al T. (Department: 2154)
Electrical computers and digital processing systems: memory
Storage accessing and control
C711S101000, C711S154000, C711S170000, C711S173000
Reexamination Certificate
active
06249837
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a memory and a microcomputer including the memory; and more especially, the invention relates to a composition of the memory and the microcomputer in which the amount of current dissipation is reduced.
Generally, in the case where a processor using a memory has a high-speed processing mode and a low-speed processing mode, a memory having a high-speed access operation is used to accommodate the high-speed processing mode of the microcomputer. That is, even if the microcomputer operates in the low-speed processing mode, the memory maintains its maximum operational speed. Therefore, the conventional memory works at its maximum operational speed and consumes a current proportional to the number of switching operations performed in the memory, even when it is possible for the memory to operate at a lower operational speed. This operational feature of the memory impedes a reduction of current dissipated in the memory or the processor using it.
Although a single chip microcomputer capable of operating in either a high-speed processing mode or a low-speed processing mode is disclosed in JP-A-259986/1994, its mode changing method is different from the present invention, and it does not have the ability to directly control the memory access speed of its memory.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a memory and a microcomputer which are effective to reduce the current dissipated in the memory and the microcomputer.
One feature of a memory according to the present invention is that the memory has a high-speed access mode in which the memory access speed is high, but the current dissipation amount is large, and a small current mode in which the memory access speed is lower than that in the high-speed access mode, but the current dissipation amount is small.
Another feature of the memory having a high-speed access mode in which the memory access speed is high, but the current dissipation amount is large, and a small current mode in which the memory access speed is lower than that in the high-speed access mode, but the current dissipation amount is small, is that the memory further includes a control circuit for controlling the memory to operate either in the high-speed access mode or in the small current mode in accordance with a commend received from outside of the memory.
Another feature of the memory having a high-speed access mode in which the memory access speed is high, but the current dissipation amount is large, and a small current mode in which the memory access speed is lower than that in the high-speed access mode, but the current dissipation amount is small, is that the memory further includes a control circuit for controlling each memory block, established by dividing the address space of the memory into a plurality of memory blocks, to operate either in the high-speed access mode or in the small current mode in accordance with a command received from outside of the memory.
Still another feature of the memory according to the present invention is that the address space of the memory is divided into at least two regions including a high-speed access operating region in which the memory access speed is high, but the current dissipation amount is large, and a small current operating region in which the memory access speed is lower than that in the high-speed access mode, but the current dissipation amount is small, and the memory further includes a control circuit for switching the operational state for each of the regions to an active state or an inactive state in accordance with a command received from outside of the memory.
Furthermore, a microcomputer to attain the above object of the present invention includes one of the above-mentioned features.
In accordance with the present invention, the dissipation current in a memory and a microcomputer can be reduced by operating the memory in the small current mode during a period in which high-speed memory access is not required.
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Kida Hiroyuki
Sugai Masaru
Tsuchiya Masahiro
An Meng-Al T.
Antonelli Terry Stout & Kraus LLP
El-Hady Nabil
Hitachi , Ltd.
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