Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 53
10.10 Power Reduction Register
The Power Reduction Register (PRR), see ”PRR0 – Power Reduction Register 0” on page 56, 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 peripheral, which is done by clearing the bit in PRR, puts the peripheral in the same state
as before shutdown.
Peripheral 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.
10.11 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.
10.11.1 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 ”ADC - Analog-to-digital converter” on page 243 for details on ADC operation.
10.11.2 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 ”AC - Analog Comparator” on page 240 for details on how
to configure the Analog Comparator.
10.11.3 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 61 for details on how to configure the Brown-out Detector.
10.11.4 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 turned on again, the user must allow the
reference to start up before the output is used. If the reference is kept on in sleep mode, the output can be used
immediately. Refer to ”Internal Voltage Reference” on page 62 for details on the start-up time.
10.11.5 Watchdog Timer
If the Watchdog Timer is not needed in the application, the module should be turned off. If the Watchdog Timer
is enabled, 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 ”Watchdog Timer” on page 63 for
details on how to configure the Watchdog Timer.