44
8025I–AVR–02/09
ATmega48P/88P/168P/328P
7.11
Register Description
7.11.1
SMCR – Sleep Mode Control Register
The Sleep Mode Control Register contains control bits for power management.
• Bits 7..4 Res: Reserved Bits
These bits are unused bits in the ATmega48P/88P/168P/328P, 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
Note:
1. Standby mode is 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.
7.11.2
MCUCR – MCU Control Register
• Bit 6 – BODS: BOD Sleep
The BODS bit must be written to logic one in order to turn off BOD during sleep, see
. Writing to the BODS bit is controlled by a timed sequence and an enable bit,
BODSE in MCUCR. To disable BOD in relevant sleep modes, both BODS and BODSE must first
Bit
7
6
5
4
3
2
1
0
–
–
–
–
SM2
SM1
SM0
SE
SMCR
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
External Standby
Bit
7
6
5
4
3
2
1
0
–
BODS
BODSE
PUD
–
–
IVSEL
IVCE
MCUCR
Read/Write
R
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0