107
8331B–AVR–03/12
Atmel AVR XMEGA AU
8.3.4
Standby Mode
Standby mode is identical to power down, with the exception that the enabled system clock
sources are kept running while the CPU, peripheral, and RTC clocks are stopped. This reduces
the wake-up time.
8.3.5
Extended Standby Mode
Extended standby mode is identical to power-save mode, with the exception that the enabled
system clock sources are kept running while the CPU and peripheral clocks are stopped. This
reduces the wake-up time.
8.4
Power Reduction Registers
The power reduction (PR) registers provide a method to stop the clock to individual peripherals.
When this is done, the current state of the peripheral is frozen and the associated I/O registers
cannot be read or written. Resources used by the peripheral will remain occupied; hence, the
peripheral should be disabled before stopping the clock. Enabling the clock to a peripheral again
puts the peripheral in the same state as before it was stopped. This can be used in idle mode
and active modes to reduce the overall power consumption. In all other sleep modes, the periph-
eral clock is already stopped.
Not all devices have all the peripherals associated with a bit in the power reduction registers.
Setting a power reduction bit for a peripheral that is not available will have no effect.
8.5
Minimizing Power Consumption
There are several possibilities to consider when trying to minimize the power consumption in an
AVR MCU controlled system.
In general, correct sleep modes should be selected and used to
ensure that only the modules required for the application are operating
.
All unneeded functions should be disabled. In particular, the following modules may need spe-
cial consideration when trying to achieve the lowest possible power consumption.
8.5.1
Analog-to-Digital Converter - ADC
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
conversion will be an extended conversion. Refer to
”ADC – Analog-to-Digital Converter” on
for details on ADC operation.
8.5.2
Analog Comparator - AC
When entering idle mode, the analog comparator should be disabled if not used. 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,
irrespective
of
”AC – Analog Comparator” on page 398
for details on how to configure the
analog comparator.
8.5.3
Brownout Detector
If the brownout detector is not needed by the application, this module should be turned off. If the
brownout detector is enabled by the BODLEVEL fuses, it will be enabled in all sleep modes, and
always consume power. In the deeper sleep modes, it can be turned off and set in sampled
mode to reduce current consumption. Refer to
”Brownout Detection” on page 115
for details on
how to configure the brownout detector.
