well, you could do this:
(a has the tile)
cp a,2
jp m,passable ;if it's less then 2(the 'm'(minus)) go to
passable
cp a,(what ever the max number for nonpassable)
jp m,not_passable
;continue on if you have "special" tiles
I hope that helps ^_^
the jp m, bassically checks to see if it's less then the number.