Internal PLL

PIC18F2455/2550/4255/4550 devices include a Phase Locked Loop (PLL) circuit. This is provided specifically for USB applications with lower speed oscillators and can also be used as a microcontroller clock source.

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mynameisdan said:

I'm running the PIC18F4550 on a 20Mhz crystal, is there any way I can use the PLL to run it at 40Mhz? I'm a bit confused on the fuse settings, as it seems the PLL is only for USB?

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        CONFIG	FOSC = HSPLL_HS               ; XT oscillator, XT used by USB
	CONFIG	CPUDIV = OSC1_PLL2	      ; Divide PLL output by 2 (96MHz/2 = 48 MHz clock for CPU)
	CONFIG	PLLDIV = 2		      ; PLL Divide by 2 (8MHz Crystal)