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ATTINY20-XUR

8-bit AVR Microcontroller with 2K Bytes In-System Programmable Flash

Atmel Corporation 

7.1.2

ADC Noise Reduction Mode

When bits SM[2:0] are written to 001, the SLEEP instruction makes the MCU enter ADC Noise Reduction mode, stopping

the CPU but allowing the ADC, the external interrupts, TWI and the watchdog to continue operating (if enabled). This

sleep mode halts clkI/O, clkCPU, and clkNVM, while allowing the other clocks to run.

This mode 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.

7.1.3

Power-down Mode

When bits SM[2:0] are written to 010, the SLEEP instruction makes the MCU enter Power-down mode. In this mode, the

oscillator is stopped, while the external interrupts, TWI and the watchdog continue operating (if enabled). Only a

watchdog reset, an external level interrupt on INT0, a pin change interrupt, or a TWI slave 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 bits SM[2:0] are written to 100, 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. This reduces wake-up time, because the oscillator is

already running and doesn't need to be started up.

7.2 Software BOD Disable

When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 19-5 on page 161), the BOD is actively

monitoring the supply voltage during a sleep period. In some devices it is possible to save power by disabling the BOD by

software in Power-Down and Stand-By sleep modes. 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 MCU Control Register, see “MCUCR – MCU Control Register”

on page 26. 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, see “MCUCR – MCU Control Register” on page 26.

7.3 Power Reduction Register

The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 27, provides a method to reduce

power consumption by stopping the clock to individual peripherals. When the clock for a peripheral is stopped then:

z The current state of the peripheral is frozen.

z The associated registers can not be read or written.

z Resources used by the peripheral will remain occupied.

The peripheral should in most cases be disabled before stopping the clock. Clearing the PRR bit wakes up the peripheral

and puts it in the same state as before shutdown.

Peripheral shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption.

See “Supply Current of I/O Modules” on page 174 for examples. In all other sleep modes, the clock is already stopped.

ATtiny20 [DATASHEET] 24

Atmel-8235F-AVR-ATtiny20-Datasheet_09/2014

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