TNC-Pi is a terminal node controller device, GPIO add-on board used by amateur radio operators to participate in AX.25 packet radio networks.
TNC-Pi is a special version of TNC-X designed to interface directly with the Raspberry Pi computer. It can connect to the Pi either via the Pi's serial port or via the I2C protocol. In the latter case, a single Pi can support multiple TNC-Pi's at the same time, since each TNC-Pi can be given a unique I2C address.
The TNC-Pi features a 9 pin D-Sub port and GPIO through port allowing TNC-Pis to be stacked.
For more information visit www.tnc-x.com/TNCPi.htm
I have very limited time currently for the comments, so you will probably get a very slow response for questions I know the answer to. If I need to set up a Pi to check your issue or request then I am unlikely to have chance to spend time on this.
I will continue support once I can spare the time again.
Thank you for your interest