ATmega165 datasheet(32/336 Pages) ATMEL

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ATmega165/V

2573G–AVR–07/09

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 consumption to the application’s requirements.

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

save, or Standby) will be activated by the SLEEP instruction. See Table 14 for a sum-

mary. 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 con-

tents 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.

Figure 11 on page 23 presents the different clock systems in the ATmega165, and their

distribution. The figure is helpful in selecting an appropriate sleep mode.

Sleep Mode Control Register –

SMCR

The Sleep Mode Control Register contains control bits for power management.

• Bits 3, 2, 1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0

These bits select between the five available sleep modes as shown in Table 14.

Note:

1. Standby mode is only recommended for use with external crystals or resonators.

• Bit 1 – SE: Sleep Enable

The SE bit must be written to logic one to make the MCU enter the sleep mode when the

SLEEP instruction is executed. To avoid the MCU entering the sleep mode unless it is

the programmer’s purpose, it is recommended to write the Sleep Enable (SE) bit to one

just before the execution of the SLEEP instruction and to clear it immediately after wak-

ing up.

Bit

7654

321

–

SM2

SM1

SM0

SMCR

Read/Write

R/W

Initial Value

0000

000

Table 14. Sleep Mode Select

SM2

SM1

SM0

Sleep Mode

Idle

ADC Noise Reduction

Power-down

Power-save

Reserved

Standby(1)

Reserved

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