12.3.3 Main Clock After Reset

After any Reset, the Main Clock (CLK_MAIN) is provided by the 20 MHz Oscillator (OSCHF) with a prescaler division factor of 6.

The actual OSCHF frequency is determined by the Frequency Select bits (FREQSEL) of the Oscillator Configuration fuse (FUSE.OSCCFG). Refer to the description of the FUSE.OSCCFG fuse for details of the possible frequencies after Reset.