dspic33EP with external clock source

[nazoa]

Hello,
We need to clock a dspic33pe from an external clock source and I am looking for suggestions on the fuse settings. We have a 20MHz external clock and we plan to connect this to the OSC1 pin. The question is how do I set the EC (external clock) mode but also use the internal PLL to give the 140MHz for the internal instruction clock. Will the following work?

#FUSES EC
#FUSES PR_PLL //??

Thanks

[gaugeguy]

I don't have that part, but probably use the setup_oscillator function and let it set the fuses.
setup_oscillator(OSC_CLOCK, 20M, 140M);

[Ttelmah]

You don't.
The key is that the PLL operation is not done in fuses. It has to be setup
by the code at the start of the boot. So the #use delay has to specify the
oscillator and required clock frequencies, and this then programs the PLL