![](http://datasheet.mmic.net.cn/30000/MQ83C154CXXX-12-883_datasheet_2377115/MQ83C154CXXX-12-883_41.png)
41
2593O–AVR–02/12
ATmega644
8.6
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 the Timer/Counter2 is not using the asynchronous clock, the Timer/Counter Oscillator is
stopped during sleep. If the 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 the Timer/Counter2.
8.7
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.
8.8
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 mode with the exception that the Oscillator is kept running. From Extended Standby
mode, the device wakes up in six clock cycles.
8.9
Power Reduction Register
vidual peripherals to reduce power consumption. The current state of the peripheral is frozen
and the I/O registers can not be read or written. Resources used by the peripheral when stop-
ping the clock will remain occupied, hence the peripheral should in most cases be disabled
before stopping the clock. Waking up a module, which is done by clearing the bit in PRR, puts
the module in the same state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
sleep modes, the clock is already stopped.
8.10
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.