09-30-1997,Frank Sexton wrote to Will Honea:
FS> I personally consider it the video manufactures fault because
FS> they know it causes problems with the installed base of
FS> serial I/O cards (with COM4) and don't fix it. Others say
FS> that since there are no real "official" specs for COM4 and
FS> that since the video card simply doesn't decode enough of
FS> the address that the video guys are not at fault.
Video cards DO decode the whole address.  The problem is that 8 bit
cards, especially older ones, do NOT (I know, I built some that way,
too).  The conflicts I see are that the serial card and video card both
respond to the 16 bit address and the conflicting outputs clobber you. 
Also, some systems will run serial i/o quite nicely on com4 (2e8) IF
you run from a full screen session or you don't make ANY screen outputs
(hard to do, but possible).  Anyway, we are really talking about a
conflict of growth.  The 8514 was designed for MCA, which required all
addresses to be decoded.  Somebody decided to build it for ISA where
established practice was to only decode 10 bits and here we are.  Heck,
I've got a Logitech bus mouse that conflicts with some video boards, so
it's not just serial i/o, it's the whole design compatibility (or lack
thereof) problem.
Will Honea
whonea@codenet.net
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