ATmega16 datasheet(31/315 Pages) ATMEL

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ATmega16(L)

2466E–AVR–10/02

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 SPI, USART, Analog Comparator, ADC, Two-

wire Serial Interface, Timer/Counters, Watchdog, and the interrupt system to continue

operating. This sleep mode basically halts clkCPU 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 Sta-

tus Register – ACSR. This will reduce power consumption in Idle mode. If the ADC is

enabled, a conversion starts automatically when this mode is entered.

ADC Noise Reduction

Mode

When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter

ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the External Inter-

rupts, the Two-wire Serial Interface address watch, Timer/Counter2 and the Watchdog

to continue operating (if enabled). This sleep mode basically halts clk

I/O, clkCPU, and clk-

FLASH, while allowing the other clocks to run.

This improves the noise environment for the ADC, enabling higher resolution measure-

ments. If the ADC is enabled, a conversion starts automatically when this mode is

entered. Apart form the ADC Conversion Complete interrupt, only an External Reset, a

Watchdog Reset, a Brown-out Reset, a Two-wire Serial Interface Address Match Inter-

rupt, a Timer/Counter2 interrupt, an SPM/EEPROM ready interrupt, an External level

interrupt on INT0 or INT1, or an external interrupt on INT2 can wake up the MCU from

ADC Noise Reduction 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, the Two-wire Serial Interface address watch, and the Watchdog continue

operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, a

Two-wire Serial Interface address match interrupt, an External level interrupt on INT0 or

INT1, or an External interrupt on INT2 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 level must be held for some time to wake up the MCU. Refer to “External Inter-

rupts” on page 64 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 reset time-out period, as described in “Clock Sources” on page 23.

Power-save Mode

When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter

Power-save mode. This mode is identical to Power-down, with one exception:

If Timer/Counter2 is clocked asynchronously, i.e., the AS2 bit in ASSR is set,

Timer/Counter2 will run during sleep. The device can wake up from either Timer Over-

flow or O u tput Compar e ev ent fr om T im e r/ Cou n ter2 if the cor r e spon ding

Timer/Counter2 interrupt enable bits are set in TIMSK, and the Global Interrupt Enable

bit in SREG is set.

If the Asynchronous Timer is NOT clocked asynchronously, Power-down mode is rec-

ommended instead of Power-save mode because the contents of the registers in the

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