Datasheet

7701F–AVR–10/12

Atmel ATtiny24/44/84 [Preliminary]

8.9 Register Description

8.9.1 MCUCR – MCU Control Register

The MCU Control Register contains control bits for power management.

• Bit 7 – BODS: BOD Sleep

In order to disable BOD during sleep (see Table 8-1 on page 34) the BODS bit must be written

to logic one. This is controlled by a timed sequence and the enable bit, BODSE in MCUCR.

First, both BODS and BODSE must be set to one. Second, within four clock cycles, BODS

must be set to one and BODSE must be set to zero. The BODS bit is active three clock cycles

after it is set. A sleep instruction must be executed while BODS is active in order to turn off the

BOD for the actual sleep mode. The BODS bit is automatically cleared after three clock cycles.

• Bit 5 – SE: Sleep Enable

The SE bit must be written to logical 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 pro-

grammer's purpose, it is recommended to set the sleep enable (SE) bit just before the

execution of the SLEEP instruction and to clear it immediately after waking up.

• Bits 4, 3 – SM1..0: Sleep Mode Select Bits 2..0

These bits select between the three available sleep modes as shown in Table 8-2 on page 38.

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

• Bit 2 – BODSE: BOD Sleep Enable

The BODSE bit enables setting of BODS control bit, as explained on BODS bit description.

BOD disable is controlled by a timed sequence.

Bit 76543210

BODS

PUD SE SM1 SM0 BODSE IS C 0 1 ISC00 MCUCR

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

Initial Value 0 0 0 0 0 0 0 0

Table 8-2. Sleep Mode Select

SM1 SM0 Sleep Mode

00Idle

0 1 ADC Noise Reduction

1 0 Power-down

1 1 Standby

(1)