Selectable 8/16 bit DMA channels for "ISA" bus
First Claim
1. In a personal computer having both 8-bit and 16-bit DMA channels, apparatus for selectively converting the 16-bit DMA channels to 8-bit DMA channels comprising:
- storage means for storing an 8-bit/16-bit mode signal for a 16-bit DMA channel for selecting whether said 16-bit channel is to operate as an 8-bit or 16-bit channel, said mode signal remaining set in one of said 8-bit or 16-bit modes while said 16-bit DMA channel is active such that said 16-bit DMA channel operates as an 8-bit or 16-bit channel throughout its active cycle;
page address means responsive to the stored mode signal for said channel for addressing a 64kB storage space if the mode signal is 8-bit mode and for addressing a 128kB storage space if the mode signal is 16-bit mode;
byte address means responsive to the stored mode signal for said channel for addressing a 64kB storage space in one byte intervals if the mode signal is 8-bit mode and for addressing a 128kB storage space in two byte intervals if the mode signal is 16-bit mode.
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Accused Products
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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Citations
9 Claims
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1. In a personal computer having both 8-bit and 16-bit DMA channels, apparatus for selectively converting the 16-bit DMA channels to 8-bit DMA channels comprising:
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storage means for storing an 8-bit/16-bit mode signal for a 16-bit DMA channel for selecting whether said 16-bit channel is to operate as an 8-bit or 16-bit channel, said mode signal remaining set in one of said 8-bit or 16-bit modes while said 16-bit DMA channel is active such that said 16-bit DMA channel operates as an 8-bit or 16-bit channel throughout its active cycle; page address means responsive to the stored mode signal for said channel for addressing a 64kB storage space if the mode signal is 8-bit mode and for addressing a 128kB storage space if the mode signal is 16-bit mode; byte address means responsive to the stored mode signal for said channel for addressing a 64kB storage space in one byte intervals if the mode signal is 8-bit mode and for addressing a 128kB storage space in two byte intervals if the mode signal is 16-bit mode. - View Dependent Claims (2, 3, 4)
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5. In a personal computing system having an AT or ISA bus architecture, apparatus for selectively switching 16-bit DMA channels between operation as 16-bit DMA channels and operation as 8-bit DMA channels, said apparatus comprising:
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register means for storing at least one 8-bit/16-bit mode bit for at least one of the 16-bit DMA channels for selecting whether said at least one 16-bit channel is to operate as an 8-bit or 16-bit channel, said at least one mode bit remaining set in one of said 8-bit or 16-bit modes while said at least one 16-bit DMA channel is active such that said at least one 16-bit DMA channel operates as an 8-bit or 16-bit channel throughout its active cycle; 16-bit DMA control means responsive to a 16-bit mode bit for addressing 64kB addresses with a two byte storage space at each address; paging means responsive to said DMA control means and a 16-bit mode bit for inhibiting the addressing of a 64kB storage space and enabling the addressing of an 128kB storage space; said DMA control means responsive to an 8-bit mode bit stored in said register means for addressing 64kB addresses with a single byte storage space at each address; said paging means responsive to said DMA control means and a 8-bit mode bit for enabling the addressing of a 64kB storage space and inhibiting the addressing of an 128kB storage space. - View Dependent Claims (6, 7, 8)
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9. In a personal computing system having an "AT" or "ISA" bus architecture designed for attachment to 8-bit or 16-bit peripheral devices, DMA channel apparatus for executing DMA cycles comprising:
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a first DMA controller responsive to 8-bit peripheral devices for controlling 8-bit DMA data transfers in one byte address space intervals within a 64k byte storage space; a second DMA controller coupled to said first DMA controller such that said second DMA controller is responsive to 16-bit peripheral devices for controlling 16-bit DMA data transfers in two byte address space intervals within a 128k byte storage space; a page register responsive to an active first DMA controller for addressing storage space as pages with each page having 64k bytes of storage space; said page register responsive to an inactive first DMA controller for addressing storage space as pages with each page having 128k bytes of storage space; a control register for storing an 8-bit/16-bit mode bit for selecting whether a DMA channel coupled to said second DMA controller is to operate as an 8-bit or 16-bit channel, said mode bit remaining set in one of said 8-bit or 16-bit modes while said DMA channel is active such that said DMA channel operates as an 8-bit or 16-bit channel throughout its active cycle; said second DMA controller responsive to an 8-bit peripheral device and an 8-bit mode bit from said control register for controlling 8-bit DMA transfers in one byte address space intervals within a 64k byte storage space; and said page register responsive to an active second DMA controller and an 8-bit mode bit from said control register for addressing storage space as pages with each page having 64k bytes of storage space.
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Specification