AT90USB646 datasheet(55/456 Pages) ATMEL

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7593L–AVR–09/12

AT90USB64/128

8.7.2

PRR1 – Power Reduction Register 1

• Bit 7 - PRUSB: Power Reduction USB

Writing a logic one to this bit shuts down the USB by stopping the clock to the module. When

waking up the USB again, the USB should be re initialized to ensure proper operation.

• Bit 6..4 - Res: Reserved bits

These bits are reserved and will always read as zero.

• Bit 3 - PRTIM3: Power Reduction Timer/Counter3

Writing a logic one to this bit shuts down the Timer/Counter3 module. When the Timer/Counter3

is enabled, operation will continue like before the shutdown.

• Bit 2..1 - Res: Reserved bits

These bits are reserved and will always read as zero.

• Bit 0 - PRUSART1: Power Reduction USART1

Writing a logic one to this bit shuts down the USART1 by stopping the clock to the module.

When waking up the USART1 again, the USART1 should be re-initialized to ensure proper

operation.

8.8

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.

8.8.1

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 “ADC – Analog to Digital Converter” on

page 307 for details on ADC operation.

8.8.2

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 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 “Analog Comparator” on page 304 for details on how to configure the Analog

Comparator.

Bit

6543

PRUSB

–––PRTIM3

–

PRUSART1

PRR1

Read/write

R/W

RRRR/W

R/W

Initial value

0000

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