ATmega328P datasheet(39/345 Pages) ATMEL

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7810A–AVR–11/09

ATmega328P [Preliminary]

9.5

Power-down Mode

When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter

Power-down mode. In this mode, the external Oscillator is stopped, while the external interrupts,

the 2-wire Serial Interface address watch, and the Watchdog continue operating (if enabled).

Only an External Reset, a Watchdog System Reset, a Watchdog Interrupt, a Brown-out Reset, a

2-wire Serial Interface address match, an external level interrupt on INT0 or INT1, or a pin

change interrupt can wake up the MCU. This sleep mode basically halts all generated clocks,

allowing operation of asynchronous modules only.

Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed

level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 61

for details.

When waking up from 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, as described in “Clock Sources” on page 26.

9.6

Power-save Mode

When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter

Power-save mode. This mode is identical to Power-down, with one exception:

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, Power-down mode is recommended instead of 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. Note that even if the synchronous clock is running in Power-save, this

clock is only available for Timer/Counter2.

9.7

Standby Mode

When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the

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

with the exception that the Oscillator is kept running. From Standby mode, the device wakes up

in six clock cycles.

9.8

Extended Standby Mode

When the SM2..0 bits are 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 with the exception that the Oscillator is kept running. From Extended Standby

mode, the device wakes up in six clock cycles.

ATmega328P Datasheet(PDF) 39 Page - ATMEL Corporation

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