ATtiny1624/1626/1627
External Clock Sources
These external clock sources are available:
- External Clock from a pin
(EXTCLK).
- The TOSC1 and TOSC2 pins are dedicated to driving a 32.768 kHz crystal
oscillator (XOSC32K).
- Instead of a crystal oscillator, TOSC1 can be configured to accept
an external clock source.