ATMEGA48 datasheet(39/374 Pages) ATMEL

39 / 374 page

2545J–AVR–12/06

ATmega48/88/168

Power Management and Sleep Modes

Sleep modes enable the application to shut down unused modules in the MCU, thereby saving

power. The AVR provides various sleep modes allowing the user to tailor the power consump-

tion to the application’s requirements.

8.1

Sleep Modes

Figure 7-1 on page 27 presents the different clock systems in the ATmega48/88/168, and their

distribution. The figure is helpful in selecting an appropriate sleep mode. Table 8-1 shows the

different sleep modes and their wake up sources.

Notes:

1. Only recommended with external crystal or resonator selected as clock source.

2. If Timer/Counter2 is running in asynchronous mode.

3. For INT1 and INT0, only level interrupt.

To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a

SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register select

which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save, or Standby) will be

activated by the SLEEP instruction. See Table 8-2 on page 43 for a summary.

If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU

is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and

resumes execution from the instruction following SLEEP. The contents of the Register File and

SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode,

the MCU wakes up and executes from the Reset Vector.

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 the SPI, USART, Analog Comparator, ADC, 2-wire Serial

Interface, Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep

mode basically halts clk

CPU and clkFLASH, while allowing the other clocks to run.

Table 8-1.

Active Clock Domains and Wake-up Sources in the Different Sleep Modes.

Active Clock Domains

Oscillators

Wake-up Sources

Sleep Mode

Idle

X(2)

ADC Noise

Reduction

X(2)

X(3)

XX(2)

Power-down

X(3)

Power-save

X(2)

X(3)

Standby(1)

XX(3)

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