13.2 Sleep Modes

The following table shows the different sleep modes, BOD disable ability, and their wake-up sources.

Table 13-1. Active Clock Domains and Wake-Up Sources in the Different Sleep Modes
Sleep Mode	Active Clock Domains						Oscillators		Wake-Up Sources								Software BOD Disable
Sleep Mode	clk_CPU	clk_FLASH	clk_IO	clk_ADC	clk_ASY	clk_PTC	Main Clock  Source Enabled	Timer Oscillator  Enabled	INT and PCINT	TWI Address  Match	Timer2	SPM/EEPROM Ready	ADC	WDT	USART⁽⁴⁾	Other I/O	Software BOD Disable
Idle			Yes	Yes	Yes	Yes	Yes	Yes⁽²⁾	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
ADC Noise Reduction				Yes	Yes	Yes	Yes	Yes⁽²⁾	Yes⁽³⁾	Yes	Yes⁽²⁾	Yes	Yes	Yes	Yes
Power-Down									Yes⁽³⁾	Yes				Yes	Yes		Yes
Power-Save					Yes	Yes	Yes⁽⁵⁾	Yes⁽²⁾	Yes⁽³⁾	Yes	Yes			Yes	Yes		Yes
Standby⁽¹⁾							Yes		Yes⁽³⁾	Yes				Yes	Yes		Yes
Extended Standby					Yes⁽²⁾	Yes	Yes	Yes⁽²⁾	Yes⁽³⁾	Yes	Yes			Yes	Yes		Yes

Note:

Only recommended with external crystal or resonator selected as the clock source.
If Timer/Counter2 is running in Asynchronous mode.
For INT1 and INT0, only level interrupt.
Start frame detection only.
The main clock is kept running if PTC is enabled.

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.

ATmega328PB

13.2 Sleep Modes