balun. The switch is driven by the RFCTRL1 and RFCTRL2 pins of the ATSAMR21G18A, which feature

Antenna Diversity to enable the device to automatically select the best signal from two antennas (can also

be selected manually). The output of the switch is connected to a ceramic chip antenna (Johanson

Technology, 2540AT18D0100) and a SMA connector for external antennas.

Table 4-10. RF Connections

Pin on SAM R21

RF

Shared functionality

RFP

RF balanced output (positive)

RFN

RF balanced output (negative)

PA09 / RFCTRL1

RF switch control signal (negative)

EDBG

PA12 / RFCTRL2

RF switch control signal (positive)

EDBG

4.3.

1.8V Operation

The SAM R21 Xplained Pro board is operated at 3.3V by default, but it also has the possibility of running

at lower voltages from an external supply. The EDBG is designed to run from a 3.3V supply and won't

work on other voltages, therefore all connections from the EDBG and the on board 3.3V regulator to the

ATSAMR21G18A have to be removed. Figure 4-1 1.8V Operation Modifications shows all components

that have to be removed for 1.8V operation.

When the components are removed the kit can be supplied with a desired voltage through the pins

marked 3V3 (pin four) and GND (pin two) on the power header described in Xplained Pro Power Header.

To program and debug the ATSAMR21G18A a 2x5 50mil header has to be mounted above EXT1 as

shown in Figure 1-1 SAM R21 Xplained Pro Evaluation Kit Overview.

Note: 

Operating the SAM R21 Xplained Pro on other voltages than 3.3V requires physical modifications on the

kit using a soldering iron and an external debugger for programming the ATSAMR21G18A.

The on board LED is selected for 3.3V operation, the light level at 1.8V operation is very low. To increase

the emitted light level the value of the series resistor can be lowered.

The EDBG functionality can be restored by re-soldering the removed components, they are all 0Ω

resistors.

Important: 

The voltage supplied through the power header is applied directly to the ATSAMR21G18A and

the extension headers. Applying a voltage greater than 3.3V may damage the board

permanently.

Atmel SAM R21 Xplained Pro [USER GUIDE]

Atmel-42243D-SAM-R21-Xplained-Pro_User Guide-04/2016

16