The Unified Program and Debug Interface (UPDI) is an Atmel proprietary interface for external programming and on-chip debugging of a device. It is a successor to the PDI 2-wire physical interface, which is found on all AVR XMEGA devices. UPDI is a single-wire interface providing a bi-directional half-duplex asynchronous communication with the target device for purposes of programming and debugging.
When designing an application PCB, which includes an Atmel AVR with the UPDI interface, the pinout shown below should be used. One of the 6-pin adapters provided with the Atmel-ICE kit can then be used to connect the Atmel-ICE probe to the application PCB.
Figure 1. UPDI Header Pinout