The Unified Program and Debug Interface (UPDI) is a Microchip proprietary interface for external programming and on-chip debugging of a device. It is a successor to the PDI two-wire physical interface, which is found on all AVR XMEGA devices. UPDI is a one-wire interface providing a bidirectional half-duplex asynchronous communication with the target device for purposes of programming and debugging.
When designing an application PCB, which includes a Microchip 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