User Manual

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ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
8271E–AVR–07/2012
10.8 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 with the exception that the
Oscillator is kept running. From Extended Standby mode, the device wakes up in six clock cycles.
10.9 Power Reduction Register
The Power Reduction Register (PRR), see ”PRR – Power Reduction Register” on page 44, 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 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 power consump-
tion. In all other sleep modes, the clock is already stopped.
10.10 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 par-
ticular, the following modules may need special consideration when trying to achieve the lowest possible power
consumption.
10.10.1 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.
Refer to ”Analog-to-Digital Converter” on page 242 for details on ADC operation.
10.10.2 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. Refer to ”Analog Comparator” on page 239 for details on how to configure
the Analog Comparator.
10.10.3 Brown-out Detector
If the Brown-out Detector is not needed by the application, this module should be turned off. If the Brown-out
Detector 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. Refer to
”Brown-out Detection” on page 48 for details on how to configure the Brown-out Detector.