AT90USB82 datasheet(41/306 Pages) ATMEL

41 / 306 page

7707D–AVR–07/08

AT90USB82/162

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.

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, Power-down, Power-save, Standby or Extended standby) will be acti-

vated by the SLEEP instruction. See Table 8-1 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.

Figure 6-1 on page 25 presents the different clock systems in the AT90USB82/162, and their

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

8.0.1

Sleep Mode Control Register – SMCR

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

• Bit 7-4 - Reserved bits

These bits are reserved and will always read as zero.

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

These bits select between the five available sleep modes as shown in Table 8-1.

Note:

1. Standby modes are only recommended for use with external crystals or resonators.

• Bit 0– 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

Bit

––

SM2

SM1

SM0

SMCR

Read/Write

R/W

Initial Value

Table 8-1.

Sleep Mode Select

SM2

SM1

SM0

Sleep Mode

Idle

Reserved

Power-down

Power-save

Reserved

Standby

(1)

Extended Standby

(1)

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