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