Hmmm.

I just ordered some PIC16C771JWs to experiment with.  Can someone give
me a reference to how to avoid this OSCAL problem / capture the data and
write it back when I want to erase and reuse these PICs?  The
www.microchips.com website returns zilch on a search for 'OSCAL'.

Ted Mawson

======================================
Mark Newland wrote...

The chips are not useless.  They just won't run at the same speed as
they did from the factory unless you put the same value back in for
OSCCAL.  You could do a series of "guesses" with calculations in between
until you have the correct oscillator speed (or at least a speed close
enough for your application).

A quick check of my 12C509 data sheets shows that changing the OSCCAL
value from one extream to the other moves the frequency about 250,000 Hz
(at room
temperature). Temperature and supply voltage can change the internal
frequency even more than that of changing OSCCAL.  If you really need a
more accurate clock for the processor, use a crystal or resonator.  If
not, don't worry about OSCCAL too much.  Your programs will still run.

> Sean Alcorn - Avion Sydney wrote:

> Hi all,
>
> When I first started mucking around with PICs, I bought 6 x
PIC12C509A/JW
> and 6 x PIC12C671/JW - which are not cheap devices. I have since found
out
> that erasing these with a UV Eraser actually erases the OSCCAL data
for the
> internal clock.
>
> Apparently, I should have read this data when the chips were new,
recorded
> the number for each chip, then re-written the calibration data each
time I
> write to that particular chip. This I did not do. :-(
>
> Is there any method of retreiving this data or are the chips useless?
I
> assume that I can still use them with an extenal clock, but then that
leaves
> less I/O.
>
> Regards,
>
> Sean
>
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