• Bit 6 - PRTIM2: Power Reduction Timer/Counter2
Writing a logic one to this bit shuts down the Timer/Counter2 module in synchronous
mode (AS2 is 0). When the Timer/Counter2 is enabled, operation will continue like
before the shutdown.
• Bit 5 - PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the
Timer/Counter0 is enabled, operation will continue like before the shutdown.
• Bit 4 - Res: Reserved bit
This bit is reserved in ATmega48/88/168 and will always read as zero.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the
Timer/Counter1 is enabled, operation will continue like before the shutdown.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
Writing a logic one to this bit shuts down the Serial Peripheral Interface by stopping the
clock to the module. When waking up the SPI again, the SPI should be re initialized to
ensure proper operation.
• Bit 1 - PRUSART0: Power Reduction USART0
Writing a logic one to this bit shuts down the USART by stopping the clock to the mod-
ule. When waking up the USART again, the USART should be re initialized to ensure
proper operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before
shut down. The analog comparator cannot use the ADC input MUX when the ADC is
shut down.
Minimizing Power
Consumption
There are several possibilities to consider when trying to minimize the power consump-
tion 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 particu-
lar, the following modules may need special consideration when trying to achieve the
lowest possible power consumption.
Analog to Digital Converter
Analog Comparator
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 Con-
verter” on page 231 for details on ADC operation.
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 Ref-
erence will be enabled, independent of sleep mode. Refer to “Analog Comparator” on
page 228 for details on how to configure the Analog Comparator.
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
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ATmega48/88/168
2545D–AVR–07/04