Datasheet

ATmega16U4/32U4 [DATASHEET]

Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016

7.9 Register Description

7.9.1 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 six available sleep modes as shown in Table 7-2.

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 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 waking up.

7.9.2 Power Reduction Register 0 - PRR0

• Bit 7 - PRTWI: Power Reduction TWI

Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When waking up the TWI

again, the TWI should be re initialized to ensure proper operation.

• Bit 6 - Res: Reserved bit

This bits is reserved and will always read as zero.

Bit 76543210

––––SM2SM1SM0SESMCR

Read/Write R R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 7-2. Sleep Mode Select

SM2 SM1 SM0 Sleep Mode

0 0 0 Idle

0 0 1 ADC Noise Reduction

0 1 0 Power-down

0 1 1 Power-save

1 0 0 Reserved

1 0 1 Reserved

1 1 0 Standby

(1)

1 1 1 Extended Standby

(1)

Bit 7654321 0

PRTWI – PRTIM0 – PRTIM1 PRSPI – PRADC PRR0

Read/Write R/W R R/W R R/W R/W R R/W

Initial Val-

0000000 0