Do you have some 'noisy' circuit coupling into the RC?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

----- Original Message -----
From: Mark Moldavsky <mmoldav@VISONIC.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, September 19, 2000 2:43 AM
Subject: Re: [PIC]: pic16c505 oscillator stability


> 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.
> > >
> > > --
> > > http://www.piclist.com hint: To leave the PICList
> > > mailto:piclist-unsubscribe-request@mitvma.mit.edu
> > >
> > >
> > >
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's
>
>

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
"[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's