XENIX/386 memory mapping

[ALUN SAUNDERS]

Hi there,
 
A colleague of mine is having trouble adressing an encryption board
installed in a 386 machine running XENIX/386. It works OK under DOS
and can be got at by adressing a RAM buffer at D800:0.  All attempts
to find this lump of memory when running under XENIX seem to fail.
 
I must admit, I'm a DOS type, so I don't have a clue as to what the
problem might be, but I know the 386 can do some pretty strange things
with memory mapping and the like.  One thing that puzzles me is that
it is an 8-bit card, i.e. only one edge connector, so wouldn't you get
strange adress conflicts due to the fact that the card can only decode
20 bits of adress ? Come to think of it how does any 286 or 386
protected mode system cope with cards of this sort, such as video
controllers or EMS cards for example ?
 
So, if anybody can give me a hint as to what sort of things I should
look at, I'd be grateful.
 
Alun Saunders