Delphi rs232 ComPort Libraries

 

These components have demo applications which act as terminals with full
duplex capability. See:

http://www.torry.net/authorsmore.php?id670
http://www.torry.net/pages.php?id8
http://sourceforge.net/projects/tpapro/
http://sourceforge.net/projects/comport/

Have a look at the source code and try the demos on your hardware to see
what works best for you.