The HC12 is backward compatible with the HC11 (apparently), but it also
has a larger address bus or multiplexing scheme to address up to 5megs
of memory. This would be handy for building a cut/uncut type XY map to
allow the robot to do a thorough job.
The HC12 is also much faster than the HC11. Some information about the
HC12 can be found at the PARTS homepage
http://www.rdrop.com/~marvin/
Dave Everett.