Chris, I have used 4MHz in RC mode a few times with no problems
with a 16F84, used a 22pf ceramic cap and a 4.7k resistor. It measured
within about 5% of 4MHz on the cro.

Page 83 of the 16C84 datasheet has a good graph of rc values vs
speed etc. You can get the datasheet on the microchip.com site.
- Roman




> On Sat, 23 Sep 2000, Chris Pringle wrote:
>
> > Hmm, you know your stuff. Well, I'm trying to clock this thing at 10MHz, but
> > with not much succes. The book says to use a Resistor in series with a
> > capacitor with OSC1 connected between the 2. I used values of 10K and 50pF
> > for the Res. and Cap. Are these ok? I'm currently using MPLAB with a
> > PICSTART Plus. The manual written by Microchip seems to be absolutly fine,
> > except I couldn't get it to work. Although, one of the pieces of literature
> > from Microchip seems to say something slightly different (values differ),
> > however it was rather old, so I ignored it and used the later document. The
> > latest copy says to use values between 3K and 100K and anything above 20pF.
> > If what I've used is correct, then my problem is more likely to be a circuit
> > error which I can't find.
> >
>
> 10MHz !
>
> I never tried to go that high with an RC circuit. Has anyone else? Try backing
> off to say 100 or 200 kHz and see if that's easier. I'm not sure how accurate
> you wish to get the clock, but 50pF is relatively small and there is going to be
> several pF of stray capacitance.
>
> BTW, in RC mode you should see fclk/4 on osc2. You may want to see if that is
> really there. If it is, then you know that the clock is running. Then after
> that it's all software...
>
> Scott

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