ATtiny261A datasheet(35/292 Pages) ATMEL

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8197A–AVR–10/09

ATtiny261A/461A/861A

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.

7.1.2

ADC Noise Reduction Mode

When the SM1:0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC Noise

Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, and the

Watchdog to continue operating (if enabled). This sleep mode halts clkI/O, clkCPU, and clkFLASH,

while allowing the other clocks to run.

This mode improves the noise environment for the ADC, enabling higher resolution measure-

ments. If the ADC is enabled, a conversion starts automatically when this mode is entered. Apart

form the ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a

Brown-out Reset, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or a pin

change interrupt can wake up the MCU from ADC Noise Reduction mode.

7.1.3

Power-Down Mode

When the SM1:0 bits are written to 10, the SLEEP instruction makes the MCU enter Power-

down mode. In this mode, the Oscillator is stopped, while the external interrupts, and the Watch-

dog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out

Reset, an external level interrupt on INT0, or a pin change interrupt can wake up the MCU. This

sleep mode halts all generated clocks, allowing operation of asynchronous modules, only.

7.1.4

Standby Mode

When the SM1:0 bits are written to 11 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.

7.2

Software BOD Disable

When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 18-4 on page

168), the BOD is actively monitoring the supply voltage during a sleep period. It is possible to

save power by disabling the BOD by software in Power-Down sleep mode. The sleep mode

power consumption will then be at the same level as when BOD is globally disabled by fuses.

If BOD is disabled by software, the BOD function is turned off immediately after entering the

sleep mode. Upon wake-up from sleep, BOD is automatically enabled again. This ensures safe

operation in case the VCC level has dropped during the sleep period.

When the BOD has been disabled, the wake-up time from sleep mode will be approximately

60µs to ensure that the BOD is working correctly before the MCU continues executing code.

BOD disable is controlled by the BODS (BOD Sleep) bit of BOD Control Register, see “MCUCR

– MCU Control Register” on page 37. Writing this bit to one turns off BOD in Power-Down and

Stand-By, while writing a zero keeps the BOD active. The default setting is zero, i.e. BOD active.

Writing to the BODS bit is controlled by a timed sequence and an enable bit, see “MCUCR –

MCU Control Register” on page 37.

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