Datasheet
42.5.1 External Clock Source
Figure 42-5. External Clock Source Example Schematic
XOUT/GPIO
XIN
NC/GPIO
External
Clock
Table 42-4. External Clock Source Connections
Signal Name Recommended Pin Connection Description
XIN XIN is used as input for an external clock signal Input for inverting oscillator pin
XOUT/GPIO Can be left unconnected or used as normal GPIO
42.5.2 Crystal Oscillator
Figure 42-6. Crystal Oscillator Example Schematic
XOUT
XIN
15pF
15pF
The crystal should be located as close to the device as possible. Long signal lines may cause a load too
high to operate the crystal, and cause crosstalk to other parts of the system.
Table 42-5. Crystal Oscillator Checklist
Signal Name Recommended Pin Connection Description
XIN Load capacitor 15pF
(1)(2)
External crystal between 0.4 to 30MHz
XOUT Load capacitor 15pF
(1)(2)
1. These values are given only as typical examples.
2. Decoupling capacitor should be placed close to the device for each supply pin pair in the signal
group.
42.5.3 External Real Time Oscillator
The low frequency crystal oscillator is optimized for use with a 32.768kHz watch crystal. When selecting
crystals, load capacitance and crystal’s Equivalent Series Resistance (ESR) must be taken into
consideration. Both values are specified by the crystal vendor.
The SAM D21 oscillator is optimized for very low power consumption, so pay close attention when
selecting crystals. See the table below for maximum ESR recommendations on 9pF and 12.5pF crystals.
The low-frequency crystal oscillator provides an internal load capacitance of typical values available in
Table , 32kHz Crystal Oscillator Characteristics. This internal load capacitance and PCB capacitance can
SAM D21 Family
Schematic Checklist
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 1167