Uno R3 grounding problem

I have a UNO R3 that I am trying to connect to using the serial I/O interface and using a monitor program on a windows computer to do the communications to the device. The device I'm trying to connect to is a QRPLabs ProgRock frequency synthesizer. The manual shows how to connect the I/O and grounds lines between the two units to enable communication. This doesn't work. I noticed that I have 2 choices for the ground connection on either side of the board. The QRP forum mentions that the choice of where to make the ground will affect the I/O interfacing! Has anyone found this problem or something like it?

Can you provide a link to the manual of the synthesizer so we know what you're talking about?

Just throwing this into the mix

Section on STAR grounds applies more to audio circuits.

Can you please post the code you are attempting to use and a circuit diagram showing how you have everything connected?

Thanks.. Tom... :grinning: :+1: :coffee: :australia: