Brian Scearce wrote:
>
> I don't think this is specifically PIC-related, so please feel free
> to reply to me privately if you think the list wouldn't be interested
> in your answer.
>
> I was having a problem the other day where my 20MHz 16C63/JW seemed
> to be running at more like 6-7MHz.  I wrote up a description of
> the problem and almost submitted it to the list, but then I decided
> to spend $0.75 of my own money buying another 20MHz crystal first.
> Sure enough, the new crystal works fine.
>
> I suspect and hope that the first crystal was just mislabelled.
> Or is this something that could happen again?  Can damage to a
> crystal change its frequency, rather than just break it?
>
> Further details: I have no oscilloscope, but as far as my
> blinkenlights
> programs showed, the first crystal worked steadily and reliably,
> just at the wrong rate.  I have the OSC1/OSC2 capacitors installed
> as recommended in the data book (22pF), and the OSC TYPE bits are
> set to "HS" (assuming that the Picstart Plus software is doing its
> job).  I don't think it's a marginal 16C63; I'm using two of them,
> and in any case the new 20MHz crystal works with both.
>
> Brian

I believe that what you are seeing is the wrong capacitive load on the
xtal.
Try replacing the 30pf? capacitors with say 20pf capacitors.
I have found xtals 20Mhz and above very fussy about the capacitive load.

regards

--
Lee McLaren                          lmclaren@trumpet.com.au
Comstra pty. ltd.                    lmclaren@comstra.com.au
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'It was five hours of Boggs's "channelling". After three hours
I asked him to summon up the soul of Jimi Hendrix and requested
All Along the Watchtower. You know, the guy's been dead
twenty years but he still hasn't lost his edge'
Mulder