"mame <machine> -<rs232 slot> null_modem -bitbngr socket.127.0.0.1:4321" then connect with a telnet client.

You could also use terminal rather than null_modem but if the machine has it's own input then keystrokes will go to both which makes it a bit unusable.

Edit: beaten

Last edited by crazyc; 06/01/16 01:10 PM.