ATMEGA640 datasheet(52/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

11.8 Power Reduction Register

The Power Reduction Register (PRR), see “PRR0 – Power Reduction Register 0” on page 55 and “PRR1 – Power

Reduction Register 1” on page 56, provides a method for stopping the clock to individual peripherals to reduce

power consumption.

Note that 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 peripherals (for example I/O pin, etc.) will remain occupied

The peripheral should in most cases be disabled before stopping the clock. Waking up a module, which is done by

cleaning the bit in PRR, puts the module in the same state as before shutdown. Module shutdown can be used in

Idle mode or Active mode to significantly reduce the overall power consumption. See “Power-down Supply Cur-

rent” on page 380 for examples. In all other sleep modes, the clock is already stopped.

11.9 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.

11.9.1

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 268 for details on ADC operation.

11.9.2

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 265 for details on how to

configure the Analog Comparator.

11.9.3

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 59 for details on how to configure the Brown-out Detector.

11.9.4

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 60 for details on the start-up time.

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