External clock and PLL feature on PIC18F47J13

Thread Starter


Joined Oct 29, 2009
I pretty much always use the internal clock on a Pic. I need accuracy on my latest project so I intend to use an external crystal.

What is the best way to validate that my Pic is running at the expected clock speed? I see that this Pic can output the clock on RB0. Is a possible way to use my scope on that pin to verify the clock?

I am a little confused on the PLL feature. The datasheet says:

The PIC18F47J13 Family has additional prescalers and
postscalers, which have been added to accommodate a
wide range of oscillator frequencies. The PIC18F47J13
provides two PLL circuits: a 4x multiplier PLL and a
96 MHz PLL enabling 48 MHz operation from the 8 MHz
internal oscillator. Figure 3-1 provides an overview of the
oscillator structure.

Does this mean if I use this feature, my actual clock will be 4X whatever crystal that I select? Is there a limit on the frequency of crystal can be used?


Joined Jul 4, 2015
For most PIC18Fs 64 MHz is th elimit for Fosc with 4x PLL. 16 MHz x 4 = 64 MHz. 96 MHz / 2 = 48 MHz is used internally for USB clock.