1) verify the byte you give to the port: copy the character you write to sdat to a memory location, then by whatever debugging means you have (I hope ICE) check it.
2) for debugging and possible inclusion put a test for the port being ready in front of your write to sdat EVEN IF you "know" that it is not needed.
3) as you can read, your speed settings are ok, check if the PC require CTS, DTR or some such thing.