Datasheet

• If Timer/Counter0 is clocked asynchronously, i.e. the AS0 bit in ASSR is set, Timer/Counter0 will

run during sleep. The device can wake up from either Timer Overflow or Output Compare event

from Timer/Counter0 if the corresponding Timer/Counter0 interrupt enable bits are set in TIMSK,

and the global interrupt enable bit in SREG is set.

If the asynchronous timer is NOT clocked asynchronously, Power-down mode is recommended instead of

Power-save mode because the contents of the registers in the asynchronous timer should be considered

undefined after wake-up in Power-save mode if AS0 is 0.

This sleep mode basically halts all clocks except clk

ASY

, allowing operation only of asynchronous

modules, including Timer/Counter0 if clocked asynchronously.

14.6. 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 6 clock cycles.

14.7. 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 mode

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

in six clock cycles.

14.8. Minimizing Power Consumption

There are several issues to consider when trying to minimize the power consumption in an AVR

controlled system. In general, sleep modes should be used as much as possible, and the sleep mode

should be selected so that as few as possible of the device’s functions are operating. All functions not

needed should be disabled. In particular, the following modules may need special consideration when

trying to achieve the lowest possible power consumption.