ATmega1284P datasheet(43/380 Pages) ATMEL

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8059D–AVR–11/09

ATmega1284P

8.10

Power Reduction Registers

The Power Reduction Registers (PRR0 and PRR1), see page 46, 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 dis-

abled before stopping the clock. Waking up a module, which is done by clearing the bit in

PRR0/PRR1, 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 consumption. In all other sleep modes, the clock is already stopped.

8.11

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.

8.11.1

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

conversion will be an extended conversion. Refer to ”ADC - Analog-to-digital Converter” on page

240 for details on ADC operation.

8.11.2

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 237 for details on how to configure the Ana-

log Comparator.

8.11.3

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 sig-

nificantly to the total current consumption. Refer to ”Brown-out Detection” on page 51 for details

on how to configure the Brown-out Detector.

8.11.4

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 Volt-

age Reference” on page 52 for details on the start-up time.

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