ATtiny261-ESSZ datasheet(35/227 Pages) ATMEL

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7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

Power Management and Sleep Modes

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

ideal choice for low power applications.

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.

8.1

Sleep Modes

Figure 7-1 on page 25 presents the different clock systems in the ATtiny261/461/861, and their

distribution. The figure is helpful in selecting an appropriate sleep mode. Table 8-1 shows the

different sleep modes and their wake up sources.

Note:

1. For INT0 and INT1, only level interrupt.

To enter any of the three 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 8-2 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.

8.2

Idle Mode

When the SM1..0 bits 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 clk

CPU and clkFLASH, while

allowing the other clocks to run.

Idle mode enables the MCU to wake up from external triggered interrupts as well as internal

ones like the Timer Overflow. If wake-up from the Analog Comparator interrupt is not required,

the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator

Control and Status Register – ACSR. This will reduce power consumption in Idle mode. If the

ADC is enabled, a conversion starts automatically when this mode is entered.

Table 8-1.

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

Active Clock Domains

Oscillators

Wake-up Sources

Sleep Mode

Idle

XXX

ADC Noise

Reduction

X(1)

XXX

Power-down

(1)

Standby

X(1)

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