Re: Help needed: Emulation of AppleII Graphic modes

[me@lazilong.com (Lazarus I. Long)]

jon@i-manila.com (Jon Co) wrote

> I remember reading somewhere that the bits on the right edge in DHR
> affects the display on the other side
IIRC, there are screen holes at what seems like either edge of the
screen.  these "screen holes" are areas of memory (between the
scanlines) that are not visible on the screen.  sneaky programmers and
parts of the OS store data there to save space.  but you can't use the
byte (actually the high bit) that resides in memory just before the
byte at the left edge of the screen.  if you set this byte's high bit,
and the low bit is set too, AND the first onscreen byte's high bit is
set, that low bit from the byte before the left edge of the screen
will shift onscreen, giving you a different color than you're
expecting. :)

> because I can't find that document anymore.  Looked at the //c
> technical reference manual did not reveal anything although i was sure
> thats where I first saw it.
there is lots more info on the technical HGR stuff here:
http://www.lazilong.com/apple_II/a2pix/
see the "explaination" and the "long winded inqiry"

> also Is it possible to set DHR to monochrome mode with soft switches
> so that it displays 560-dot monochrome display or do I have to turn
> down the color knob physically?
you will enjoy this:
http://home.neo.rr.com/goeagles/tniigs29.txt

-laz aka davec