XMEGAA datasheet(97/445 Pages) ATMEL

97 / 445 page

8077H–AVR–12/09

XMEGA A

8.3.4

Standby Mode

Standby mode is identical to Power-down with the exception that the enabled system clock

sources are kept running, while the CPU, Peripheral and RTC clocks are stopped. This reduces

the wake-up time.

8.3.5

Extended Standby Mode

Extended Standby mode is identical to Power-save mode with the exception that the enabled

system clock sources are kept running while the CPU and Peripheral clocks are stopped. This

reduces the wake-up time.

8.4

Power Reduction Registers

The Power Reduction (PR) registers provides a method to stop the clock to individual peripher-

als. When this is done the current state of the peripheral is frozen and the associated I/O

registers cannot be read or written. Resources used by the peripheral will remain occupied;

hence the peripheral should in most cases be disabled before stopping the clock. Enabling the

clock to a peripheral again, puts the peripheral in the same state as before it was stopped. This

can be used in Idle mode and Active mode to reduce the overall power consumption signifi-

cantly. In all other sleep modes, the peripheral clock is already stopped.

Not all devices have all the peripherals associated with a bit in the power reduction registers.

Setting a power reduction bit for a peripheral that is not available will have no effect.

8.5

8.5.1

CTRL- Sleep Control Register

• Bit 7:4 - Reserved

These bits are unused and reserved for future use. For compatibility with future devices, always

write these bits to zero when this register is written.

• Bit 3:1 - SMODE[2:0]: Sleep Mode Selection

These bits select sleep modes according to Table 8-2 on page 97.

Bit

7654321

+0x00

----

SMODE[2:0]

SEN

CTRL

Read/Write

RRRR

R/W

Initial Value

0000000

Table 8-2.

Sleep mode

SMODE[2:0]

SEN

Group Configuration

Description

XXX

OFF

No sleep mode enabled

000

IDLE

Idle Mode

001

Reserved

010

PDOWN

Power-down Mode

011

PSAVE

Power-save Mode

100

Reserved

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