User Manual

Atmel SAM R21 Xplained Pro [USER GUIDE]
42243B-MCU-06/2014
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cutting the strap and adding a resistor across the strap. More information about oscillator allowance and safety
factor can be found in appnote AVR4100
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.
Note
The 16MHz crystal is connected directly to the RF die inside the SAM R21. The clock signal
generated by the crystal is routed from the CLKM pin on the RF die to a GCLK IO pin on the
microcontroller. For more information on how the RF die is connected to the microcontroller and
how to configure the CLKM pin see the SAM R21 datasheet.
Table 4-5. External 32.768kHz Crystal
Pin on SAM R21 Function
PA00 XIN32
PA01 XOUT32
Table 4-6. External 16MHz Crystal
Pin on SAM R21 Function
XTAL1 XIN
XTAL2 XOUT
4.2.2 Mechanical Buttons
SAM R21 Xplained Pro contains two mechanical buttons. One button is the RESET button connected to the
SAM R21 reset line and the other is a generic user configurable button. When a button is pressed it will drive
the I/O line to GND.
Table 4-7. Mechanical Buttons
Pin on SAM R21 Silkscreen text
RESETN RESET
PA28 SW0
4.2.3 LED
There is one yellow LED available on the SAM R21 Xplained Pro board that can be turned on and off. The LED
can be activated by driving the connected I/O line to GND.
Table 4-8. LED Connections
Pin on SAM R21 LED
PA19 Yellow LED0
4.2.4 USB
The SAM R21 Xplained Pro has a Micro-USB receptable for use with the SAM R21 USB module. To be able to
detect when a USB cable is connected, a GPIO / ADC is used to detect the VBUS voltage on the connector.
Table 4-9. USB Connections
Pin on SAM R21 USB
PA07 VBUS Detection
PA24 USB D-
PA25 USB D+
4.2.5 RF
The main feature of SAM R21 Xplained Pro is to show the RF capability of the ATSAMR21G18A device.
This device has bidirectional 100ohm differential antenna pins, which are fed through a balun (Johanson
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http://www.atmel.com/images/doc8333.pdf