ATmega32U2 datasheet(42/314 Pages) ATMEL

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7799B–AVR–07/09

ATmega8U2/16U2/32U2

Power Management and Sleep Modes

9.1

Overview

Sleep modes enable the application to shut down unused modules in the MCU, thereby saving

power. The AVR provides various sleep modes allowing the user to tailor the power consump-

tion to the application’s requirements.

9.2

Sleep Modes

Figure 8-1 on page 26 presents the different clock systems in the ATmega8U2/16U2/32U2, and

their distribution. The figure is helpful in selecting an appropriate sleep mode. shows the differ-

ent sleep modes and their wake up sources.

Notes:

1. Only recommended with external crystal or resonator selected as clock source.

2. For INT[7:4], only level interrupt.

3. Asynchronous USB interrupt is WAKEUPI only.

To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a

SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register select

which sleep mode (Idle, Power-down, Power-save, Standby or Extended standby) will be acti-

vated by the SLEEP instruction. See Table 9-2 for a summary.

If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU

is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and

resumes execution from the instruction following SLEEP. The contents of the Register File and

SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode,

the MCU wakes up and executes from the Reset Vector.

9.3

Idle Mode

When the SM2:0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle mode,

stopping the CPU but allowing the USB, SPI, USART, Analog Comparator, Timer/Counters,

Table 9-1.

Active Clock Domains and Wake-up Sources in the Different Sleep Modes.

Active Clock

Domains

Oscillators

Wake-up Sources

Sleep Mode

Idle

XXX

Power-down

X(2)

Power-save

X(2)

Standby(1)

XX(2)

Extended

Standby

XX(2)

ATmega32U2 Datasheet(PDF) 42 Page - ATMEL Corporation

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