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 SPI, USART, Analog Comparator, ADC, Two-
wire Serial Interface, 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 Sta-
tus Register – ACSR. This will reduce power consumption in Idle mode. If the ADC is
enabled, a conversion starts automatically when this mode is entered.