: (key)
    ( inc then fetch )
    [ ACIAR> LITN ] C@ 1+ [ ACIA_BUFSZ 1- LITN ] AND
    ( As long as R> == W>-1, it means that buffer is empty )
    BEGIN DUP [ ACIAW> LITN ] C@ = NOT UNTIL
    DUP [ ACIA( LITN ] @ + C@ ( ridx c )
    SWAP [ ACIAR> LITN ] C! ( c )
;
: (emit)
    ( As long at CTL bit 1 is low, we are transmitting. wait )
    BEGIN [ ACIA_CTL LITN ] PC@ 0x02 AND UNTIL
    ( The way is clear, go! )
    [ ACIA_IO LITN ] PC!
;