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Originally Posted by 6600gt
The PIC's have an internal hardware PLL(Phase Loop Lock hardware multiplier). I can't find the setup of this of RC but if you connect a 10MHz crystal to a pic and turn on hardware PLL, its like running 40 MHz crystal.(Don't ask me how it does it, I have no clue, try the data sheet) But they might have just hooked it up directly to a 40MHz clock, I guess you can do it.
I see this everywhere Foso/4, I am guessing but I think it means frequency of the oscillator(clock). I might be screwing up the technical terms.
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It sounds like you're still a little unclear on how this stuff works.
The PIC18F8720 (and presumably others) has a PLL as an option. This allows you to multiply the frequency of the oscillator that is used as the clock source. Whether IFI impliments this or not, I don't know (their website only quotes 10MIPS). So, if we have a 10MHz crystal and take advantage of the PLL, the PIC sees a 40MHz crystal. The datasheet mentions that this would be good to do of you are worried about having external high frequency signals.
The Foso/4 you see refers to what the PIC does with the clock. Each instruction cycle is 4 clock cycles. If you connect a 40MHz crystal, instructions are 10MHz. The details should be in the datasheet, but in essence, it takes the processor 4 clock cycles to process an instruction.
What you need to take away from this: The PIC in the RC is 10MIPS.