Glad to hear you tracked it down.
Other tricks one can generally use is to send 'U' characters in a loop, and scope the appropriate jumper to see signal.
For 9-pin RS232 you can also loop-back pins 2 and 3 to see if you can receive back data, this checks also the RS232 drivers.
Finally you're not bound to use ST's choice of 7-bit ODD Parity nonsense, I understand they were trying to demonstrate how parity worked, but the combination is practically never used in modern systems, be it GPS/GNSS receivers, or Cellular Modems.
