11.3.2 Main Clock After Reset

After any Reset, the Main Clock (CLK_MAIN) is either provided by the OSCHF and prescaled by a factor of 6 or the OSC32K. This is determined by the Clock Select (CLKSEL) bit field configuration of the Oscillator Configuration (FUSE.OSCCFG) fuse. Refer to the description of the FUSE.OSCCFG fuse for details of the possible frequencies after Reset.