4.2.1 Crystal

The SAM R21 Xplained Pro kit contains one crystal that can be used as clock source for the SAM R21 device. The crystal has a cut-strap next to it that can be used to measure the oscillator safety factor. This is done by cutting the strap and adding a resistor across the strap. More information about oscillator allowance and safety factor can be found in application note AVR4100.

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 I/O 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 R21Function
PA00XIN32
PA01XOUT32
Table 4-6. External 16MHz Crystal
Pin on SAM R21Function
XTAL1XIN
XTAL2XOUT