29 Apr
2005
29 Apr
'05
3:25 p.m.
Well, nothing that probably already hasn't been
stated before -- I know the
specifications of the Motorola 6845 and how it works, and I know that the tech
ref documents each CRTC register, etc... what I'm looking for is stuff that
probably isn't in the tech ref, like "what are the invalid settings for each
register", etc as implemented on the CGA.
That is not in the techref :-(. It doesn't even tell you how to get the
160*200 16 colour mode...
What, I suspect, you need to do is look at the schematics. Those are in
the techref, the board consists of a 6845, 16K DRAMs and a lot of TTL.
There's nothing custom (unlike the gate array in the PCjr), so it should
be possible to figure it all out.
Be warned that, of course, clone cards may not support such tricks. The
third pallette does seem to be generally available on clones, though.
-tony