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From: raymond@goedel.arc.nasa.gov (Eric A. Raymond)
Newsgroups: comp.os.msdos.programmer
Subject: Format of VGA memory
Message-ID: <8227@ptolemy.arc.nasa.gov>
Date: 26 Sep 90 00:07:42 GMT
Sender: usenet@ptolemy.arc.nasa.gov
Followup-To: comp.sys.ibm.pc.programmer
Organization: NASA Ames Research Center
Lines: 22

Actually it's the MCGA 640x480x2 mode which is also implemented on the
VGA in which I'm interested.  Basically,  I would like to know how
this memory is arranged so that I may manipulate it directly.

I'm pretty sure its base adderess is B800:0000.  There seems to be
some odd echoing of bits going on.  That is, there are two bits for
each pixel, one in each byte of a word, so when I draw a pixel at 0,0,
the WORD at B800:0000 changes to 80 80 (or is this just an artifact of
my debugger).

FYI, I'm implementing some low level routines to scroll and invert
regions on the screen.  I have some routines implemented by Turbo C's
getimage and putimage routines, but they are sloooooow.

---
Eric A. Raymond  (raymond@ptolemy.arc.nasa.gov)
G7 C7 G7 G#7 G7 G+13 C7 GM7 Am7 Bm7 Bd7 Am7 C7 Do13 G7 C7 G7 D+13: Elmore James


--
Eric A. Raymond  (raymond@ptolemy.arc.nasa.gov)
G7 C7 G7 G#7 G7 G+13 C7 GM7 Am7 Bm7 Bd7 Am7 C7 Do13 G7 C7 G7 D+13: Elmore James