44
2513L–AVR–03/2013
ATmega162/V
Extended MCU
Control Register –
EMCUCR
Bit 7 – SM0: Sleep Mode Select Bit 0
The Sleep Mode Select bits select between the five available sleep modes as shown in
TableNote:
1. Standby mode and Extended Standby mode are only available with external crystals or
resonators.
Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing the SPI, USART, Analog Comparator, Timer/Counters,
Watchdog, and the interrupt system to continue operating. This sleep mode basically halts clk-
CPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow and USART Transmit Complete interrupts. If wake-up from the
Analog Comparator interrupt is not required, the Analog Comparator can be powered down by
setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will
reduce power consumption in Idle mode.
Power-down Mode When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Power-
down mode. In this mode, the external Oscillator is stopped, while the external interrupts and the
Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-
out Reset, an External Level Interrupt on INT0 or INT1, an external interrupt on INT2, or a pin
change interrupt can wake up the MCU. This sleep mode basically halts all generated clocks,
allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs
until the wake-up becomes effective. This allows the clock to restart and become stable after
having been stopped. The wake-up period is defined by the same CKSEL Fuses that define the
Bit
765
4321
0
SM0
SRL2
SRL1
SRL0
SRW01
SRW00
SRW11
ISC2
EMCUCR
Read/Write
R/W
Initial Value
000
0000
0
Table 16. Sleep Mode Select
SM2
SM1
SM0
Sleep Mode
000
Idle
001
Reserved
010
Power-down
011
Power-save
100
Reserved
101
Reserved
110
1