11.3.3 Power-Down Mode

When the SMCR.SM is written to '0x010', the SLEEP instruction makes the MCU enter Power-Down mode. In this mode, the external Oscillator is stopped, while the external interrupts and the Watchdog continue operating (if enabled).

Only an these events can wake up the MCU:
  • Watchdog System Reset
  • External level interrupt on INT0
  • Pin change interrupt
This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.