ATmega32A datasheet(35/352 Pages) ATMEL

35 / 352 page

8155B–AVR–07/09

ATmega32A

If the Asynchronous Timer is NOT clocked asynchronously, Power-down mode is recommended

instead of Power-save mode because the contents of the registers in the Asynchronous Timer

should be considered undefined after wake-up in Power-save mode if AS2 is 0.

This sleep mode basically halts all clocks except clk

ASY, allowing operation only of asynchronous

modules, including Timer/Counter2 if clocked asynchronously.

9.6

Standby Mode

When the SM2:0 bits are 110 and an external crystal/resonator clock option is selected, the

SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down

with the exception that the Oscillator is kept running. From Standby mode, the device wakes up

in six clock cycles.

9.7

Extended Standby Mode

When the SM2:0 bits are 111 and an external crystal/resonator clock option is selected, the

SLEEP instruction makes the MCU enter Extended Standby mode. This mode is identical to

Power-save mode with the exception that the Oscillator is kept running. From Extended Standby

mode, the device wakes up in six clock cycles.

9.8

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.

9.8.1

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 “Analog to Digital Converter” on page 208

for details on ADC operation.

9.8.2

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,

independent of sleep mode. Refer to “Analog Comparator” on page 205 for details on how to

configure the Analog Comparator.

9.8.3

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 BODEN Fuse, 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 40 for details on how to

configure the Brown-out Detector.

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