Selectable 8/16 bit DMA channels for "ISA" bus
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United States of America Patent
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Nov 7, 1995
Grant Date -
N/A
app pub date -
Sep 21, 1992
filing date -
Sep 21, 1992
priority date (Note) -
Expired
status (Latency Note)
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Abstract
In a personal computing system the function of the DMA controllers in the 'AT' or 'ISA' bus has been modified so that the system may select whether the 16-bit DMA channels are to be used as 8-bit DMA channels or 16-bit DMA channels. An 8/16-bit mode bit for each of the 16-bit DMA channels is written in a control register during the system Power On Self Test routine. Once the mode bit is written for each of the three 16-bit DMA channels, it may be read when the channel is active to select whether the channel is to operate as an 8-bit or 16-bit channel. With this mode bit information available, the page addressing may be selectively changed from 128k size pages to 64k size pages when a 16-bit DMA channel is to be converted to 8-bit. In addition, the byte addressing within a page may be changed from two byte addressing during 16-bit mode to single byte addressing during 8-bit mode.
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