If the processor you used is anything like the 16c54 for serial
communications you have two problems. First, the 5volt RS232 expects an
RS232 converter to raise the signal to 12 volts AND to INVERT it.
However, not only are the 5volt signals upsidedown, but I also needed to
alter the clock constants by more than I would have expected by the
change I made in clock frequencies. I would recomend a  quick look with
an oscilloscope is called for here.
Good luck.
Gordon

G.J.Flanagan@ncl.ac.uk
Tel. 0191 222 8261
Fax. 0191 222 6442
Department of Medical Physics, Medical School, Newcastle upon Tyne NE2 4HH.