Rainbow-electronics ATmega128RFA1 Bedienungsanleitung PDF herunterladen (Seite 159)

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8266A-MCU Wireless-12/09

ATmega128RFA1

12.3 Power Reduction Register

The Power Reduction Register (PRR), see "PRR0 – Power Reduction Register0" on

page 167, "PRR1 – Power Reduction Register 1" on page 168 and "PRR2 – Power

Reduction Register 2" on page 168, provide 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 unit 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 the shutdown. Exceptions

are the SRAM blocks and the radio transceiver. The SRAM is shut down by a DRT

switch and the radio transceiver is in reset state if its respective power reduction bit is

set.

Module shutdown can be used in Idle mode and Active mode to significantly reduce the

overall power consumption. See chapter "Typical Characteristics" on page 510 for

examples. In all other sleep modes, the clock is already stopped.

12.4 Minimizing Power Consumption

There are several issues to consider when trying minimizing 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.

12.4.1 Analog to Digital Converter

If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should

be disabled before entering any sleep mode. Refer to chapter "ADC – Analog to Digital

Converter" on page 410 for details on ADC operation.

12.4.2 Analog Comparator

When entering Idle mode, the Analog Comparator should be disabled if not used. When

entering ADC Noise Reduction mode the Analog Comparator should also be disabled.

In other sleep modes, the Analog Comparator is automatically disabled. However, if the

Analog Comparator is set up to use the Internal Voltage Reference as input, the Analog

Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage

Reference will be enabled, independent of sleep mode. Refer to "AC – Analog

Comparator" on page 407 for details on how to configure the Analog Comparator.

12.4.3 Brown-out Detector

If the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be disabled in

Deep-sleep mode. Refer to "Brown-out Detection" on page 178 for details on how to

configure the Brown-out Detector. It is recommended to enable the Brown-out Detector.

12.4.4 Internal Voltage Reference

The Internal Voltage Reference will be enabled when needed by the Brown-out

Detection, the Analog Comparator or the ADC. If these modules are disabled as

described in the sections above, the internal voltage reference will be disabled and not

consume power. When turned on again, the user must allow the reference to start up

before the output is used. If the reference is kept on in sleep mode, the output can be

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