ATtiny3216/3217

10.3.3 Main Clock After Reset

After any Reset, CLK_MAIN is provided by the 16/20 MHz Oscillator (OSC20M) and 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:

Table 10-1. Peripheral Clock Frequencies 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.

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