: ACIA$
    H@ DUP DUP ACIA( ! ACIAR> !
    1+ ACIAW> !  ( write index starts one position later )
    0x20 ( buffer size ) ALLOT
    H@ ACIA) !
( setup ACIA
  CR7 (1) - Receive Interrupt enabled
  CR6:5 (00) - RTS low, transmit interrupt disabled.
  CR4:2 (101) - 8 bits + 1 stop bit
  CR1:0 (10) - Counter divide: 64 )
    0b10010110 [ ACIA_CTL LITN ] PC!
    (im1) ;

