10.3.3 Main Clock After Reset
After any Reset, CLK_MAIN is provided by the 16/20 MHz Oscillator (OSC20M), with a prescaler
division factor of 6. Since the actual frequency of the OSC20M is determined by the Frequency
Select (FREQSEL) bits of the Oscillator Configuration (FUSE.OSCCFG) fuse, these frequencies
are possible after Reset:
| CLK_MAIN as Per FREQSEL in FUSE.OSCCFG | Resulting CLK_PER |
|---|---|
| 16 MHz | 2.66 MHz |
| 20 MHz | 3.3 MHz |
See the OSC20M description for further details.