Rainbow Electronics ATmega162V - Manual (Page 41)

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ATmega162/V
2513E–AVR–09/03
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 consumption to the application’s requirements.
To enter any of the five sleep modes, the SE bit in MCUCR must be written to logic one
and a SLEEP instruction must be executed. The SM2 bit in MCUCSR, the SM1 bit in
MCUCR, and the SM0 bit in the EMCUCR Register select which sleep mode (Idle,
Power-down, Power-save, Standby, or Extended Standby) will be activated by the
SLEEP instruction. See Table 16 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 unal-
tered 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 18 on page 33 presents the different clock systems in the ATmega162, and their
distribution. The figure is helpful in selecting an appropriate sleep mode.
MCU Control Register –
MCUCR
• Bit 5 – 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 wak-
ing up.
• Bit 4 – SM1: Sleep Mode Select Bit 1
The Sleep Mode Select bits select between the five available sleep modes as shown in
Table 16.
MCU Control and Status
Register – MCUCSR
• Bit 5 – SM2: Sleep Mode Select Bit 2
The Sleep Mode Select bits select between the five available sleep modes as shown in
Table 16.
Bit 7 6 5 4 3 2 1 0
SRE SRW10 SE SM1 ISC11 ISC10 ISC01 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
Bit 7 6 5 4 3 2 1 0
JTD – SM2 JTRF WDRF BORF EXTRF PORF MCUCSR
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