Datasheet

ATtiny25/45/85 [DATASHEET]

2586Q–AVR–08/2013

7.1.2 ADC Noise Reduction Mode

When the SM[1:0] 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 clk

I/O

, clk

CPU

, and clk

FLASH

, while allowing the other clocks to run.

This improves the noise environment for the ADC, enabling higher resolution measurements. 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 SM[1:0] 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, the USI start condition detection and the Watchdog

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

interupt, 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.

7.2 Software BOD Disable

When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 20-4 on page 148), the BOD is

actively monitoring the supply voltage during a sleep period. In some devices it is possible to save power by dis-

abling 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 V

level has

dropped during the sleep period.

When the BOD has been disabled, the wake-up time from sleep mode will be the same as that for wakeing up from

RESET. The user must manually configure the wake up times such that the bandgap reference has time to start

and the BOD is working correctly before the MCU continues executing code. See SUT[1:0] and CKSEL[3:0] fuse

bits in table “Fuse Low Byte” on page 149

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

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 Regis-

ter” on page 37.