From: "A.Appleyard" <A DOT APPLEYARD AT fs2 DOT mt DOT umist DOT ac DOT uk>
Organization: Materials Science Centre
To: djgpp AT delorie DOT com
Date: Mon, 20 May 1996 09:37:53 GMT
Subject: Re: graphics: writing directly to screen
Message-ID: <8DA2994535@fs2.mt.umist.ac.uk>

  watcom353 AT aol DOT com wrote (Subject: graphics):-

> I use int 10h to set the video mode like this: union REGS regs;
> regs.w.ax=mode; int386(0x10,&regs,&regs); That works fine. ... But I can't
> get a pixel on the screen.  I've tried unsigned char *scr=0xa000; with many
> different amounts of 0s after the a. But I always get a GPF. How can I write
> to the screen. ...

The screen address 0xa0000 (with 4 zeros) is an absolute (real mode) address,
but if you write e.g. `char *scr=0xa000; scr[0]=7;' in Gnu C/C++ you are
writing to the protected mode address *0xa0000, which is a different animal.
(0xa000 with 3 zeros is the <segment> address of the screen: full address =
segment_address * 16 + offset.)