ATMEGA329P_06 Datasheet, PDF (39/360 Pages) ATMEL Corporation – 8-bit Microcontroller with 32K Bytes In-System Programmable Flash

ATmega329P/3290P
8.2 BOD Disable
8.3 Idle Mode
When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses, Table 25-3 on page 296,
the BOD is actively monitoring the power supply voltage during a sleep period. To save power, it
is possible to disable the BOD by software for some of the sleep modes, see Table 8-1 on page
38. The sleep mode power consumption will then be at the same level as when BOD is globally
disabled by fuses. If BOD is disabled in 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_CC level has dropped during the sleep period.
When the BOD has been disabled, the wake-up time from sleep mode will be approximately 60
µs to ensure that the BOD is working correctly before the MCU continues executing code.
BOD disable is controlled by bit 6, BODS (BOD Sleep) in the control register MCUCR, see
”MCUCR – MCU Control Register” on page 43. Writing this bit to one turns off the BOD in rele-
vant sleep modes, while a zero in this bit keeps BOD active. Default setting keeps BOD active,
i.e. BODS set to zero.
Writing to the BODS bit is controlled by a timed sequence and an enable bit, see ”MCUCR –
MCU Control Register” on page 43.
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing LCD controller, the SPI, USART, Analog Comparator,
ADC, USI, Timer/Counters, Watchdog, and the interrupt system to continue operating. This
sleep mode basically halts clk_CPU and clk_FLASH, 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 and USART Transmit Complete interrupts. 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 automati-
cally when this mode is entered.
8.4 ADC Noise Reduction Mode
When the SM2..0 bits 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, the USI
start condition detection, Timer/Counter2, LCD Controller, and the Watchdog to continue operat-
ing (if enabled). This sleep mode basically 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 LCD controller interrupt, USI start condition interrupt, a Timer/Counter2 interrupt, 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.
8.5 Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Power-
down mode. In this mode, the external Oscillator is stopped, while the external interrupts, the
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