Can't get 18F2221 PLL to run with INTOSC

[Charles Linquis]

Yes, and as I mentioned, I'm getting 2MHz out of OSC2. Since that is a /4 , the oscillator is in fact running 8. Only the PLL isn't working properly.

[skimask]

Yes, and as I mentioned, I'm getting 2MHz out of OSC2. Since that is a /4 , the oscillator is in fact running 8. Only the PLL isn't working properly.

I'm guessing here...the datasheet is a bit convoluted and jumps back and forth a bit...
2Mhz from OSC2 is right isn't it? OSC2 is FOsc/4, FOsc/4 is 8Mhz/4... System clock isn't FOsc in this case, it's the actual clock speed before the PLL...
Try that test program with
main:
High portb.0
pause 500
low portb.0
pause 500
goto main
.......just to see what happens. Should be one flash per second of course at 32Mhz. One flash every 4 seconds would certainly mean 8Mhz.


Also, I'm wondering if the bootloader is messing with your bits for you and shutting off your PLL!!!

[Bruce]

Have you tried OSCCON = %01110010?

[skimask]

Have you tried OSCCON = %01110010?

Don't I feel like a dipstick! Internal OSC block was never selected in the first place!!!

[Darrel Taylor]

Also, try putting the OSCCON statement before the OSCTUNE.

Additionally,
the PLL will only function when the selected output frequency
is either 4 MHz or 8 MHz (OSCCON<6:4> = 111
or 110). If both of these conditions are not met, the PLL
is disabled and the PLLEN bit remains clear (writes are
ignored).

<br>

[Bruce]

Yep I think DT just nailed it. Might be holding it off until it's in the right mode for the switch.

[Charles Linquis]

Confirmed -

Darrel, you were right again. Now that I switch to 8MHz BEFORE I enable the PLL, it
works as expected.

Thanks!

[Darrel Taylor]

S-W-W-EET!
<br>

[Charles Linquis]

And one last "Gotcha" that I forgot to mention earlier - bits 0 and 1 of
OSCCON *MUST* be set to "00".

Even though you are running off the Internal Oscillator Block, if you
enable the PLL, you have to configure for PRIMARY OSCILLATOR.

Summary -

To run off the Internal oscillator and use the 4X PLL:

Set OSCCON bits 6 through 4 for either 8MHz (111) or 4MHz (110) and OSCCON
bits 1 and 0 for PRIMARY OSCILLATOR (00)

Set OSCTUNE.6 = 1 to enable the PLL.

In that order!