Datasheet

• Watchdog System Reset

• Watchdog Interrupt

• Brown-out Reset

• Two-wire Serial Interface Address Match

• External level Interrupt on INT

• Pin Change Interrupt

This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.

Note: If a level triggered interrupt is used for wake-up from power-down, the required level must be held

long enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears

before the end of the start-up time, the MCU will still wake up, but no interrupt will be generated. The

start-up time is defined by the SUT and CKSEL Fuses.

When waking up from the Power-Down mode, there is a delay from the wake-up condition occurs until

the wake-up becomes effective. This allows the clock to restart and become stable after having been

stopped. The wake-up period is defined by the same CKSEL fuses that define the Reset time-out period.

Related Links

13. System Clock and Clock Options

14.6 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 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.

14.7 Standby Mode

When the SM[2:0] bits are written to '110' and an external crystal/resonator clock option is selected, the

SLEEP instruction makes the MCU enter Standby mode. This mode is identical to the Power-Down mode

with the exception that the oscillator is kept running. From Standby mode, the device wakes up in six

clock cycles.

14.8 Extended Standby Mode

When the SM[2:0] bits are written to '111' and an external crystal/resonator clock option is selected, the

SLEEP instruction makes the MCU enter Extended Standby mode. This mode is identical to Power-Save

mode with the exception that the oscillator is kept running. From Extended Standby mode, the device

wakes up in six clock cycles.

ATmega48A/88A/168A

Power Management and Sleep Modes

Datasheet Complete

DS40002007A-page 70