8.2
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 LCD controller, the SPI, USART, Analog Comparator,
ADC, USI, Timer/Counters, Watchdog, and the interrupt system to continue operating. This
sleep mode basically halts clkCPU 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.
8.3
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 clkI/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, 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.
8.4
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
level must be held for some time to wake up the MCU. Refer to ”External Interrupts” on page 61
for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs
until the wake-up becomes effective. This allows the clock to restart and become stable after
having been stopped. The wake-up period is defined by the same CKSEL Fuses that define the
Reset Time-out period, as described in ”Clock Sources” on page 30.
40
ATmega169P
8018A–AVR–03/06
ATMEL [ ATMEL ]
