12.3.6 Manual Tuning and Auto-Tune

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 stabilized 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.

Figure 12-3. OSCHF Auto-Tune Block Diagram

Refer to the Electrical Characteristics section for details.