The TPI (Tiny Programming Interface) found on some tinyAVR devices can download code into the memories of these devices.
The TPI interface requires two of the deviceʼs pins, TPIDATA and TPICLK, in addition to the RESET pin. On STK600, they are found on the ISP/PDI connector.
Note: TPI should only be used on-board. It is
not safe to program a device on an external board through the TPI interface. A 12V signal
is applied to the Reset pin.