: _cell! ( tilenum pos )
    2 * 0x7800 OR _ctl ( tilenum ) _data 1 _zero ;
: _lf
    XYPOS @ BEGIN ( pos )
        0 ( blank ) SWAP TUCK _cell!
        1+ DUP [ VDP_COLS LITN ] MOD NOT UNTIL
    [ VDP_COLS VDP_ROWS * LITN ] MOD XYPOS ! ;
: _bs 0 ( blank ) XYPOS @ TUCK _cell! ( pos ) 1-
    [ VDP_COLS VDP_ROWS * LITN ] MOD XYPOS ! ;