Hi people;
In my application I connect a 80C552 with com1 port of PC. I try the communication with Hyperterminal and with vsscmdemo32 ( a delphi component ). I program in C but my code is similar to yours. I don't need start my application and hyperterminal at exact same time. Also I can close and open hyperterminal and it works fine. I had two problems:
1- I changed the order between RxD and TxD signals.
2- I forgot to connect 0 volts level of micro to pin number 5 of PC (ground). When I forgot this connection I got garbled characters.

Have fun,
Alberto