The programming dialog of Atmel Studio is used to set the voltages and clock frequency. Since programming of the SAM D20 is not supported by STK600, it will not show in the device list. Therefore, when connecting to STK600 in the programming dialog, it is necessary to select a different device than SAM D20. Any device and interface (e.g. AT32UC3A0128 and JTAG) from the lists will work for setting the voltage and clock. After connecting, go to board settings to access the voltage and clock settings. Move the sliders and click "Write" to change the values. Note that all voltages are limited to 3.6V.
Figure 1. Board settings
