OK, thanks, that's probably it. The fact that it
didn't work with my
monochrome monitor may not mean much, either, as there is an external
toggle switch on the display card as well as four externally-accessible
dip switches. I did try the monitor with both toggle positions, but I
didn't play with the dip switches.
I've seen cards that could do both CGA and HGC, and maybe even EGA modes.
They had DIP switches as you are describing.
As for some software requireing a switch to be flipped - maybe it also
has a way of emulating CGA via HGC, or something. (CGA-mono is slightly
lower res (640x200 I think), and I used to have a TSR for playing CGA games
on my hercules card...it just omitted some dots around the edges. But maybe
your card can do this in hardware.)
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