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ISA DMA: Difference between revisions
Length of transfer is programmed count + 1
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(Length of transfer is programmed count + 1) |
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For the pedantic among you, the page and address registers are actually used (not in modern PC's). These registers hold the next DRAM memory address to be refreshed. The reason it is useless today is because the registers can only address 16 MB of memory with these registers, and the CPU needs to be involved to 'up' the page register per 64 KB, which it can't because the DMA controller has no ability to inform the CPU it needs to be updated, because IBM forgot to connect the pins of the DMA controller to interrupts because they cost-cut on building the original PC motherboard! (Please don't feed that sentence through a grammar checker.)
'' Please notice that the number of bytes transferred is one more than the count programmed for the channel. So programming count=0 will transfer one byte, while programming count=0xffff will transfer full 64k. ''
==[[Floppy Driver|Floppy Disk]] DMA Programming==
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