ATMEGA261 View Datasheet(PDF) - Atmel Corporation
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MFG CO.
'ATMEGA261' PDF : 226 Pages View PDF
8.3 ADC Noise Reduction Mode
When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC Noise
Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, and the
Watchdog to continue operating (if enabled). This sleep mode halts clkI/O, clkCPU, and clkFLASH,
while allowing the other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. 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, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or a pin change
interrupt can wake up the MCU from ADC Noise Reduction mode.
8.4 Power-down Mode
When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter
Power-down mode. In this mode, the 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 a pin change interrupt can wake up the
MCU. This sleep mode 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 Interrupts” on page 52
for details.
8.5 Standby Mode
When the SM1..0 bits are written to 11 and an external crystal/resonator clock option is selected,
the SLEEP instruction makes the MCU enter Standby mode. This mode is identical to
Power-down with the exception that the Oscillator is kept running. From Standby mode, the
device wakes up in six clock cycles.
8.6 Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 38, pro-
vides a method to stop the clock to individual peripherals to reduce power consumption. The
current state of the peripheral is frozen and the I/O registers can not be read or written.
Resources used by the peripheral when stopping the clock will remain occupied, hence the
peripheral should in most cases be disabled before stopping the clock. Waking up a module,
which is done by clearing the bit in PRR, puts the module in the same state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. See “Supply Current of I/O modules” on page 199 for examples. In all other
sleep modes, the clock is already stopped.
8.7 Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
36 ATtiny261/ATtiny461/ATtiny861
7753E–AVR–06/10
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