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11. PM - Power Management and Sleep Modes

11.1. Overview

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

The device provides various sleep modes allowing the user to tailor the power consumption to the

application requirements.

11.2. Sleep Modes

The following Table shows the different sleep modes and their wake-up sources.

Table 11-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes.

Sleep Mode Active Clock Domains Oscillators Wake-up Sources

clk

CPU

clk

FLASH

clk

ADC

clk

ASY

Main Clock

Source

Enabled

Timer Oscillator

Enabled

INT and PCINT TWI Address

Match

Timer2 SPM/EEPROM

Ready

ADC WDT Other I/O

Idle Yes Yes Yes Yes Yes

(2)

Yes Yes Yes Yes Yes Yes Yes

ADC Noise

Reduction

Yes Yes Yes Yes

(2)

Yes

(3)

Yes Yes

(2)

Yes Yes Yes

Power-down Yes

(3)

Yes Yes

Power-save Yes Yes Yes

(2)

Yes

(3)

Yes Yes Yes

Standby

(1)

Yes Yes

(3)

Yes Yes

Extended Standby Yes

(2)

Yes Yes

(2)

Yes

(3)

Yes Yes Yes

Note:

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

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

3. For INT2, INT1 and INT0, only level interrupt.

To enter any of the six sleep modes, the Sleep Enable bit in the Sleep Mode Control Register (SMCR.SE)

must be written to '1' and a SLEEP instruction must be executed. Sleep Mode Select bits

(SMCR.SM[2:0]) select which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save,

Standby, or Extended Standby) will be activated by the SLEEP instruction.

Note: The block diagram in the section System Clock and Clock Options provides an overview over the

different clock systems in the device, and their distribution. This figure is helpful in selecting an

appropriate sleep mode.

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.