Tune the output frequency of the OSCHF either manually or automatically against an external oscillator.
Manual Tuning
Tune the output frequency of the OSCHF up and down by writing the Oscillator Tune (TUNE) bit field in the Frequency Tune (TUNE) register. The Automatic Oscillator Tune (AUTOTUNE) bit field in the CTRLA register must remain zero.
Auto-Tune Against an External Crystal Oscillator
The OSCHF output frequency can be calibrated by automatic tuning against an external 32.768 kHz crystal oscillator. Enable auto-tune by selecting the external oscillator in the Automatic Oscillator Tune (AUTOTUNE) bit field in the CTRLA register. This will lock the TUNE register, and no manual tuning is possible. The TUNE register is updated with the latest TUNE value when AUTOTUNE is disabled.
Refer to the Electrical Characteristics section for details.