Datasheet

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PSC clock sources on page 197

EXINT - External Interrupts on page 82

10.5. Standby Mode

When the SM[2:0] bits are written to '110' and an external 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.

10.6. Power Reduction Register

The Power Reduction Register (PRR) provides a method to stop the clock to individual 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 stopping 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 corresponding bit in the 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 power

consumption. In all other sleep modes, the clock is already stopped.

10.7. Minimizing Power Consumption

There are several possibilities 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.

10.7.1. Analog to Digital Converter

If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled

before entering any sleep mode. When the ADC is turned off and on again, the next conversion will be an

extended conversion.

10.7.2. Analog Comparator

When entering Idle mode, the Analog Comparator should be disabled if not used. When entering ADC

Noise Reduction mode, the Analog Comparator should be disabled. In other sleep modes, the Analog

Comparator is automatically disabled. However, if the Analog Comparator is set up to use the Internal

Voltage Reference as input, the Analog Comparator should be disabled in all sleep modes. Otherwise,

the Internal Voltage Reference will be enabled, independent of sleep mode.

10.7.3. Brown-Out Detector

If the Brown-Out Detector (BOD) is not needed by the application, this module should be turned off. If the

BOD is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes, and hence, always

consume power. In the deeper sleep modes, this will contribute significantly to the total current

consumption.