ATtiny261A datasheet(34/292 Pages) ATMEL

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8197A–AVR–10/09

ATtiny261A/461A/861A

7. Power Management and Sleep Modes

The high performance and industry leading code efficiency makes the AVR microcontrollers an

ideal choise for low power applications. In addition, 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 consumption to the application’s requirements.

7.1

Sleep Modes

Figure 6-1 on page 24 presents the different clock systems and their distribution. The figure is

helpful in selecting an appropriate sleep mode. Table 7-1 shows the different sleep modes and

their wake up sources.

Note:

1. For INT0 and INT1, only level interrupt.

2. When PLL selected as system clock.

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

SLEEP instruction must be executed. The SM1:0 bits in the MCUCR Register select which sleep

mode (Idle, ADC Noise Reduction, Power-down, or Standby) will be activated by the SLEEP

instruction. See Table 7-2 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.

Note that if a level triggered interrupt is used for wake-up the changed level must be held for

some time to wake up the MCU (and for the MCU to enter the interrupt service routine). See

“External Interrupts” on page 49 for details.

7.1.1

Idle Mode

When bits SM1:0 are written to 00, the SLEEP instruction makes the MCU enter Idle mode,

stopping the CPU but allowing Analog Comparator, ADC, Timer/Counter, Watchdog, and the

interrupt system to continue operating. This sleep mode basically halts clkCPU and clkFLASH, while

allowing the other clocks to run.

Table 7-1.

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

Sleep Mode

Active Clock Domains

Osc.

Wake-up Sources

Idle

XXX

X(2)

XXXX

ADC Noise Reduct.

X(2)

XX(1)

Power-down

X(1)

Standby

X(1)

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