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Selectable 8/16 bit DMA channels for "ISA" bus

  • US 5,465,332 A
  • Filed: 09/21/1992
  • Issued: 11/07/1995
  • Est. Priority Date: 09/21/1992
  • Status: Expired due to Fees
First Claim
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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:

  • 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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