DMA How it work, to use in ISA bus

[juan_manuell]

Hi to all,

I need some help, i found information of how the DMA could be programmed and a short explanation of how works the DRQx and DACKx and IOR,
well there are 2 modes that i could use, 1.- Transfer 1 word every request of DMA, and in 2.- a Block of words could be transfered in one request.
well now i dont know how the DMA in the first case tell to software that the all words programmed in DMA chip were transfered, or in the second
case how DMA tell to the i/o board to put another word to transfer and in the same case before how the software know that all words were transfered.

If anyone knows were i could foud information about it, it would apreciated.
thxs

 

[Bus Master]

I remember an old DMA controller from Intel called 8237, you can aquire the datasheet on the web which will provide you with many technical points you may need (i hope this will help you).

Thanks,

 

[papyaki]

More recent DMA controlers used in PC compatible computers have an IRQ output wich is active each time a DMA channel reach his terminal count (TC). The µP then check an internal register of the DMA controler to know which channel has reach his TC and to re-configure it for the next transfert.

You can download the 80386ex user manual. This chip include a 8237 compatible DMA controler. The fonctionality of the DMA is well explained.

The file is available here : **broken link removed**, or on INTEL's site