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From: Gautier <gautier.demontmollin@maths.unine.ch>
Subject: Re: Parallel Port
Date: 2000/03/20
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> Ed Falis wrote:
> > I don't see how this could have worked for either compiler, assuming x86
> > architecture without memory-mapped I/O (which can be inferred from the
> > standard PC I/O space address used for the port base).

Maybe one compiler does automatically translate these accesses to hardware addresses
into in/out instructions and the other one doesn't...

> > You need to use port I/O instructions to read and write these addresses.
> > Take a look at Machine_Instructions_386.  If you're running on NT or Win2K,
> > it won't work in either case, because of OS hardware protection.

> > - Ed

Philippe BOURZEIX wrote:

> So I can't do it on NT neither on Win98. A chance on dos ???

Yes but even on DOS you should use the inport/outport instructions ihmo.
(ASM specialist there ?...)
E.g. for VGA/SVGA palette:
   procedure Set_Color (Color : in Color_Type; Value : in RGB_Color) is
   begin
      Outport_Byte (16#3C8#, Unsigned_8 (Color));
      Outport_Byte (16#3C9#, Unsigned_8 (Value.Red));
      Outport_Byte (16#3C9#, Unsigned_8 (Value.Green));
      Outport_Byte (16#3C9#, Unsigned_8 (Value.Blue));
   end Set_Color;

NB: DOS programs using such instructions are said (not tested myself) to run on NT,
e.g. for a multi-key interrupt. NT maybe "firewalls" all these hardware accesses
knowing they come from a DOS program.
______________________________________________________
Gautier  --  http://members.xoom.com/gdemont/gsoft.htm