Swiching Mode Charger / PWM questions

[almarsh]

I figgured it out!!! Or at least I think I did.... none the less it is working now.

I was taking a stab at different things to see what may be causing the PLL not to run.

If you notice, my OSCCON register is set to 11110010.

I changed the OSCCON to = 11110000 and the output on pin 13 is now 125k (actually 124.8k according to the scope)

And thank you for pointing out my lack of defining the oscillator and my lack of any program.

Like I mentioned, I was taking stabs at things I thought might be inhibiting my progress, so I was stripping back everything I could. I guess I went a little too far.

Thank you once again for your assistance. Higher PWM frequencies were a major hurdle in my next design stage and I had to figgure it out. It will allow my project to use much smaller components and be more efficient.

-Albert

[HenrikOlsson]

Great, I'm glad that it works!
I can't say I understand WHY though.... Setting the lower two bits of OSCCON to 00 selects the primary oscillator as the source while setting it to 10 selects the INTOSC, I thought the PIC should be run by the internal oscillator.... Oh, wait, NOW I think I see what's going on...

Look at the figure 2.8 in the datasheet. When we select INTOSC by setting the lower two bits in OSCCON to 10 we're driving the chip directly from the internal oscillator with whatever frequency we set it to. The signal comming out of the "OSCCON MUX" in the diagram is selected to drive the PIC via "Clock Control MUX".

But when we enable the PLL we have the switch the clock source from INTOSC to the Main Oscillator block (even though that's what we use with EXTERNAL crystal) so that we get the signal from the PLL (which is now driven by the internal oscillator). The "real" primary oscillator is disabled though because we've selected the INTIO67 mode via the CONFIG bits.

Anyway, I'm glad you figured it out, good luck with the rest of the project!

/Henrik.