Donald Schneider, Microchip Technology Inc.
EETimes (3/14/2012 1:38 AM EDT)
In general, describing a product as "green" means it has minimal or no harmful effect on the environment. In the case of a product that uses power, green means power use is minimal. But what is meant by "minimal" or "low power" often isn't clearly defined, partly because the requirements for a low-power microcontroller (MCU) vary, depending upon how the MCU will be used.
For example, in a battery-operated thermostat low power is primarily defined by the minimum power mode that allows the device to drive the LCD display; a reduction in power leads to extended battery life. In an electricity meter, low power refers to the active current consumed by the system during operation. An electricity meter also requires the time of day to be maintained regardless of the presence of the system’s primary power supply, for example during a power failure. Thus, MCUs with flexible power modes allow a designer to tailor system operation depending on the application.
In the past, MCUs had an active mode to allow for device operation; idle and doze modes to reduce or eliminate the CPU switching power while allowing the peripherals to operate; and sleep modes that allowed limited peripheral operation with minimal power consumption.
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