After a lot of gnashing of teeth I now have a stand alone FT8 transceiver working which uses an STM32F769 Disco board.
This project allows you to decode and send FT8 messages as shown in the attached photo.
Also, the User's Guide is attached.
The STM application interfaces directly to the Arduino on the RS-HFI . Firmware is provided for communicating with the Arrduino via a serial data connection.
Enjoy!
Charley
Charley