
40
8285B–AVR–03/11
ATmega165A/165PA/325A/325PA/3250A/3250PA/645A/645P/645
tion 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 60
s 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 –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 –Note:
1. BOD disable only available in picoPower devices ATmega165PA/325PA/3250PA/645P/6450P.
9.4
Idle Mode
When the SM2:0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle mode,
stopping the CPU but allowing the SPI, USART, Analog Comparator, ADC, USI, Timer/Coun-
ters, 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 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.
9.5
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, and the Watchdog to continue operating (if enabled).
This sleep mode basically halts clk
I/O, clkCPU, and clkFLASH, 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, USI start condition interrupt, a Timer/Counter2 interrupt, an SPM/EEPROM ready inter-
rupt, an external level interrupt on INT0 or a pin change interrupt can wake up the MCU from
ADC Noise Reduction mode.
9.6
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
USI start condition detection, and the Watchdog continue operating (if enabled). Only an Exter-
nal Reset, a Watchdog Reset, a Brown-out Reset, USI start condition interrupt, an external level
interrupt on INT0, or a pin change interrupt can wake up the MCU. This sleep mode basically
halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
for details.