Rainbow Electronics ATmega3290P_V - Manual (Page 35)

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ATmega329/3290/649/6490
2552H–AVR–11/06
The LCD controller and Timer/Counter2 can be clocked both synchronously and asyn-
chronously in Power-save mode. The clock source for the two modules can be selected
independent of each other. If neither the LCD controller nor the Timer/Counter2 is using
the asynchronous clock, the Timer/Counter Oscillator is stopped during sleep. If neither
the LCD controller nor the Timer/Counter2 is 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 LCD controller and Timer/Counter2.
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.
Power Reduction
Register The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page
38, provides a method to stop the clock to individual peripherals to reduce power con-
sumption. The current state of the peripheral is frozen and the I/O registers inaccessible.
Resources used by the peripheral when stopping the clock will remain occupied so the
peripheral should 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 reduce the overall
power consumption. In all other sleep modes, the clock is already stopped.