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when reading http://microchip.wikidot.com/8bit:ec

The EC mode has three power modes to select from. The EC mode is selected in a configuration register. The three modes include: ECH - High-power mode, 4Mhz - 32Mhz ECM - Medium-power mode, 0.5 Mhz - 4 Mhz ECL - Low-power mode, under 0.5 Mhz

I'm confused as this is not a crystal oscillator that needs an amplifier to form an oscillating circuit. What is the "power" needed for if the clock is considered as:

externally generated logic level signal and that signal used as the system clock source

Are the power options needed only when the OSC2 pin is used as an output? Maybe amplifying the signal to be re transmitted to other devices? Or is it necessary for amplifying the signal to drive the internal logic of the microcontroller?

Thanks a lot

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    \$\begingroup\$ I'm guessing 'power' is used here to mean speed / frequency.. \$\endgroup\$ – m.Alin Oct 6 '15 at 11:49
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    \$\begingroup\$ The manual for the PIC18F45k50 mentions that each mode is best suited for a certain frequency range. I guess this is really related to the power consumption of the PIC itself. Maybe, the internal circuits can be made switching faster, which is not necessary for low frequency. If the PIC runs at lower speed, it can also switch lower and save some power. In this case, you may be able run it on 0.5MHz in ECH mode, but not 16MHz in ECL mode. \$\endgroup\$ – sweber Oct 6 '15 at 12:10
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Looking at the "Section 28, Electrical Specification" portion of the PIC16F1933 datasheet (http://ww1.microchip.com/downloads/en/DeviceDoc/41364B.pdf), one can see that the PIC processor power supply current is dependent on the clock frequency.

That is, internal peripherals and the core are clocked faster with faster external clock, resulting in higher current drawn from the power pin(s).

In general, even with other oscillator options (internal HL, internal LF, crystal), higher clocking speed results in higher power dissipation.

Microchip prides itself on the XLP (Extra Low Power) Nanowatt technology, where the processor draws very little current to maximize battery life. This is achieved with a number of tricks, one of which is the reduction of oscillator frequency.

This picture shows a portion of the datasheet (Idd current draw). One can see that higher Fosc frequency results in higher current consumption.

enter image description here

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