Signature of ATT 6300 graphics

[XMP12-M.CRIPPS]

In article <682 at leah.Albany.Edu>, rds95 at leah.Albany.Edu (Robert Seals) writes:
> Yo,
>     I'm using Turbo C 1.5 to write some purportedly portable (!?)
> programs that include some graphics. My version of TC does not
> autodetect a PC6300Plus adapter/screen as being a 6300, but a cga, even
> though it does support drawing in 6300 mode when initialized
> explicitly as being 6300.
> 
>     Zo, does anyone know what kind of signature to look for to try
> to identify an ATT as being ATT?
> 

If all you're worried about is video, that's easy.  Change the video mode
to 40h (the AT&T Hi-Res mode) and do a get video mode call
(int 10h, function 0fh) to see if it returns 40h.

Alternately, write something to 0b800:6000 and see if you can
read it back (the AT&T board has 32K of video memory, the CGA has 16K).
Using these methods, your routines can support *ALL* AT&T machines with the
non-standard video boards, without being ROM dependent.

The get video mode trick may return a false positive if other manufacturers
use 40h as a mode, but I'm not aware of any.  The memory test may be true
on non-AT&T boards, but functionally the boards are probably the same, so
it wouldn't matter (The Sigma Color 400 is mapped the same as the AT&T, for
instance).

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       ^         Michael J. Cripps
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