Thank you for your answer.
Our problem is oscillator "jitter" and not slow changes in frequency. And we
found that this jitter is not present in old PICs. Why?

Oliver Broad wrote:

> Running at those speeds the old PICs RC osc made a good proximity sensor and
> I guess the present generation is little different. Presumeably there is
> capacitance from the osc pin to adjacent circuits. Is doubling the C and
> halving the R an option?
>
> Oliver.
>
> ----- Original Message -----
> From: Mark Moldavsky <mmoldav@VISONIC.COM>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Monday, September 18, 2000 5:38 AM
> Subject: [PIC]: pic16c505 oscillator stability
>
> >   Hi for all !
> >
> > When using PIC16C505 in external RC oscillator mode (RB4/OSC2/CLKOUT
> > configured to CLKOUT), frequency stability is very poor.
> > Observing CLKOUT pin with a scope we see a "frequency noise" having a
> > magnitude of about 1% of CLKOUT frequency.
> > Changing state of other I/O ports configured as inputs also changes
> > CLKOUT frequency with the same magnitude.
> > Testing the same software using PIC16C54/56 or PIC16C711 (also in
> > external RC oscillator mode) results with a very good oscillator stability
> > (no problem).
> > Testing again with 16C505 in internal RC mode (RB4/OSC2/CLKOUT
> > configured to CLKOUT) results also without any problem (frequency is
> > stable).
> >
> > Application conditions:
> > Vdd = 5volt. Room's temperature. CLKOUT frequency = 700 - 1000 khz.
> >
> > Can you explain why we have such a problem and how to avoid it ?
> >
> > Thanks advance.
> >
> > Mark.
> >
> > --
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> >
> >
> >
>
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