Power-Save Mode

When the SM[2:0] bits are written to 011, the SLEEP instruction makes the MCU enter Power-Save mode. This mode is identical to power-down, except:

If Timer/Counter2 is enabled, it will keep running during sleep. The device can wake-up from either timer overflow or output compare event from Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK2, and the global interrupt enable bit in SREG is set.

If the PTC is enabled, the main clock is kept running.

If Timer/Counter2 is not running, the Power-Down mode is recommended instead of the Power-Save mode.

The Timer/Counter2 can be clocked both synchronously and asynchronously in Power-Save mode. If Timer/Counter2 is not using the asynchronous clock, the Timer/Counter oscillator is stopped during sleep. If Timer/Counter2 is not using the synchronous clock, the clock source is stopped during sleep. Even if the synchronous clock is running in power-save, this clock is only available for Timer/Counter2.