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8183F–AVR–06/12
ATtiny24A/44A/84A
7.3
Power Reduction Register
vides a method to reduce power consumption by stopping the clock to individual peripherals.
When the clock for a peripheral is stopped then:
The current state of the peripheral is frozen.
The associated registers can not be read or written.
Resources used by the peripheral will remain occupied.
The peripheral should in most cases be disabled before stopping the clock. Clearing the PRR bit
wakes up the peripheral and puts it in the same state as before shutdown.
Peripheral shutdown can be used in Idle mode and Active mode to significantly reduce the over-
other sleep modes, the clock is already stopped.
7.4
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.
7.4.1
Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis-
abled before entering any sleep mode. When the ADC is turned off and on again, the next
details on ADC operation.
7.4.2
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 the 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 dis-
abled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,
ure the Analog Comparator.
7.4.3
Brown-out Detector
If the Brown-out Detector is not needed in 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
7.4.4
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power. When