ATmega325P datasheet(38/364 Pages) ATMEL

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8023F–AVR–07/09

ATmega325P/3250P

Power Management and Sleep Modes

9.1

Overview

Sleep modes enable the application to shut down unused modules in the MCU, thereby saving-

power. The AVR provides various sleep modes allowing the user to tailor the power

consumption to the application’s requirements.

When enabled, the Brown-out Detector (BOD) actively monitors the power supply voltage during

the sleep periods. To further save power, it is possible to disable the BOD in some sleep modes.

See ”BOD Disable” on page 39 for more details.

9.2

Sleep Modes

Figure 8-1 on page 29 presents the different clock systems in the ATmega325P/3250P, and

their distribution. The figure is helpful in selecting an appropriate sleep mode. Table 9-1 shows

the different sleep modes, their wake up sources and BOD disable ability.

Notes:

1. Only recommended with external crystal or resonator selected as clock source.

2. If Timer/Counter2 is running in asynchronous mode.

3. For INT0, only level interrupt.

To enter any of the sleep modes, the SE bit in SMCR must be written to logic one and a SLEEP

instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register select which

sleep mode will be activated by the SLEEP instruction. See Table 9-2 on page 43 for a

summary.

If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU

is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and

resumes execution from the instruction following SLEEP. The contents of the Register File and

SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode,

the MCU wakes up and executes from the Reset Vector.

Table 9-1.

Active Clock Domains and Wake-up Sources in the Different Sleep Modes.

Active Clock Domains

Oscillators

Wake-up Sources

Sleep Mode

Idle

XXX

X(2)

XXX

ADCNRM

X(2)

X(3)

XX(2)

XXX

Power-down

X(3)

Power-save

X(2)

X(3)

Standby(1)

XX(3)

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