Debugging with Unified Program and Debug Interface (UPDI) for AVR® MCUs
Overview
The Unified Program and Debug Interface Physical Interface (UPDI PHY) provides programming and debugging through a 1-wire UART-based half-duplex interface using a single pin (either RESET or dedicated) for data reception and transmission.
In this example, an AVR® MCU supporting UPDI is used, i.e., ATtiny817. For more details about this device and its UPDI interface, see the ATtiny417 / ATtiny814 / ATtiny816 / ATtiny817 Datasheet.
The ATtiny817 Xplained Mini is used to demonstrate the UPDI interface. MPLAB® X IDE enables/disables this interface for you.
Software and Hardware Used in this Example
For the best experience, install the following in order:
Creating a Project in the IDE
From the IDE, launch the New Project Wizard by selecting File > New Project.
Follow these steps to create a new project:
Adding a File to the Project
Once a project is created, the Projects window will open.
For this example, no additional code needs to be added to main.c.
Debugging the Project
Click Debug Main Project 
to start debugging.
During device programming, you may see this warning message:
Configuration memory will not be programmed because no configuration bits settings have been defined in your code. To program configuration memory, either define the settings in your code or use the Program Configuration Bits button on the configuration memory window.
For this example, no configuration bits settings were added to the code and no device configuration bits values were changed. For more on configuration bits, see the "Reading the Configuration Bits" section.
Programming proceeds and once complete, debug mode begins.
You are now in debug mode.
Click Pause 
to halt execution temporarily or Finish Debugger Session 
to end the debug session.
Programming the Device
When you are done with debugging your code, you can program the target device by clicking Make and Program Device 
.
Reading the Configuration Bits
To set or clear device configuration bits (fuses), use the Configuration Bits window. Select Window > Target Memory Views > Configuration Bits.
When this window is first opened, all text is red and a pop-up message states that you must read the configuration bits from the device before you can edit.
Click Read Configuration Bits
on the window. The read should be successful and show this message in the mEDBF window:
Read complete
Data in the Configuration Bits window will be black and reflect the settings read from the device.
.