Method and apparatus for direct memory access in a data processing system
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United States of America Patent
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Aug 23, 1983
Grant Date -
N/A
app pub date -
Dec 30, 1980
filing date -
Dec 30, 1980
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The method and apparatus in a microprocessor-based data processing system which allows direct access to main memory associated with a central processing unit from peripheral intelligent devices such as mass storage and special processors. Main memory space is allocated in contiguous zones of actual memory and 'phantom' memory. An address decoder in connection with a bus buffer separates the peripheral from the CPU or the CPU from the peripheral whenever particular instructions are generated or address space is selected. During direct memory access, the CPU is placed in an idle state without disturbing CPU registers so that secondary functions of the CPU can be continued. The method and apparatus eliminates need for a conventional direct memory access device with its undesirably high overhead and support requirements.
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