model updown check_match<0>,d<3:0> = q<3:0>, clr<0>, ud<0>;

constant LO= 0, HI=1;

routine count;
	If clr EQL 0 then
	   d = 0 
	else 
	   begin  
	    if ud EQL 1 then 
               begin 
		d = q +1;
	        if q EQL 2 then
	       	  check_match<0> = HI
	        else
		  check_match<0> = LO; 
               end 
	    else 
               begin 
                 d = q -1;
	         if q EQL 2 then
		    check_match<0> = HI
	         else
                    check_match<0> = LO;
	       end;
           end;
endroutine;
endmodel;