ACIA3 can be used for general RS-232 except that the handshaking lines are not brought out. The TD and RD lines go through the line driver and receiver (in an MC145406) to a 3.5mm phone jack. I made a modem years ago for slow but reliable data storage on cassette, but have never really put it to use. The much faster speed, smaller size, and lower cost per bit of the newer serial EEPROMs or flash memories put the tape to shame. There is some discussion on inexpensive tape modems on the forum, under "Hardware" --> "eprom programmer:-modem topics (Garth Wilsons thread)" and "Tape modems".