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DMA and EMM386

Posted on 1997-08-22
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Last Modified: 2008-02-26
I am attempting to use DMA to transfer data from a EIA-485 card to memory and vice-versa using DMA (programming for DOS)

When I attempt to initialize the DMA controller registers, the PC gives me a

EMM386: DMA mode not supported.  Press a key to REBOOT.

message.

What's going on and how do I fix it?

Any help would be appreciated.
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Question by:RED6
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3 Comments
 
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Expert Comment

by:fozy
ID: 1013559
Try using  the Qemm Software from Quarterdeck.

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jerussa earned 100 total points
ID: 1013560
you have to remove from your config.sys de line in which is the emm386 and
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Expert Comment

by:jerussa
ID: 1013561
Yes, I have gotten the DMA to work without the EMM386.EXE loaded.

Why doesn't DMA work with EMM386 loaded though?  The 'help' documentation for EMM386.EXE specifies that a certain number of blocks are reserved for DMA buffers.  I have also read that memory managers such as EMM386 and others are supposed to trap I/O accesses to the DMA controller so that they can translate virtual memory addresses to physical addresses.

So why isn't EMM386.EXE doing this?

Also, doing this in DOS was just a way of testing the 485 card.  Ultimately, I need to do this from Windows 3.1 and Windows 95.  Do you know of any WWW documentation that may help me?

Any help would be appreciated. :)
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