Help again: output to port

[Staff-Jinghong _ Li]

(thanks for asnwers to my first post, more details here)

Help needed:  would someone tell me how to output
to a port such as a RS232 from a C program?  Any 
sepcial commands?  The address of the port is 
known, do I need to declare it as a FILE pointer? ...

Langauge : Microsoft C;
System:    MS-DOS;

Thanks so much for your attention.