The keyboard protocol is BIZARRE at best.  I designed a project very
similar to the one
which you are talking about using an HC11.  (In retrospect, I should have
used an 8051 because you can get code that already does the protocol for
it.)
To get the actual protocol, I called IBM and got them to fax me a few pages
out of a reference manual.  (Although I think I remember now that Circuit
Cellar did an article on it a year or two ago, you might want to ask there.
 http://www.circellar.com)

There are actually three different ways of doing the protocol.  I wish you
the best of luck.

Good luck,

Alan G. Smith

+---------------------------------------------------------
| Alan G. Smith
| ags@poboxes.com
| http://www.innovatus.com/ags