;course-setting subroutine
;set course to heading in AX.
!set-course
        mov     bx,     @1      ; get current desired heading
                                ; (not actual heading)
        and     ax,     255     ; Fix ax into 0-255.
        sub     ax,     bx      ; get number of degrees to turn.
        opo     14,     ax      ; turn!
        ret                     ; All done!