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'[PIC]: Calibration Data - JW Types'
2002\01\16@021925 by Sean Alcorn - Avion Sydney

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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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2002\01\16@044953 by Rudy Rudy

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Sean,

They are not useless.  But, it will be really painful to get the "correct"
OSCCAL value (the closest to 4MHz).  I have played around with 12C509, and
the OSCAL value is around b'100000'.  So, you can start your code like this:

movlw   b'100000'
movwf OSCCAL

That should have the clock pretty close to 4MHz.  And if you need it to be
as close as possible to 4MHz, write some procedures to change the OSCCAL
value when you change the input pin for example.  I never use 12C671 before,
but I am sure they are similar.

Hope that helps!

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2002\01\16@045019 by Alan B. Pearce

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>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.

There is a way of recalibrating them, I think there is a Microchip App Note
on how to, but I cannot be sure of this. I know there is information
available somewhere as I saw it when looking at these devices a long time
ago, but cannot remember exactly where I saw it.

The chips are not useless without the calibration value. You can still use
the internal oscillator, it is just that it will be off the nominal 4Mhz
frequency by some value, which is what is normally corrected by using the
OSCCAL function to bring it closer to the nominal 4Mhz. They would be fine
for any use where the timing of the PIC is non-critical.

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2002\01\16@093451 by Mark Newland

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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:

{Quote hidden}

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2002\01\16@110354 by Ted Mawson

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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
http://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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2002\01\16@210007 by Sean Alcorn - Avion Sydney

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on 17/1/02 2:50 AM, Ted Mawson at spamBeGoneTed.MawsonspamBeGonespamPORTFOLIOPM.COM wrote:

> 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
> http://www.microchips.com website returns zilch on a search for 'OSCAL'.

Ted,

As far as I know, the OSCCAL (two Cs) is unique to the 12C, 12CE and 16C505
series chips - ie; the ones that have the internal oscillator. This value is
written in to the last register in the factory, and the first instruction is
to move this value into the W register. To use this value, your first
instruction (for these parts) simply needs to be 'OSCCAL' - it is used to
calibrate the Oscillator.

I could be wrong, but I not think you have anything to worry about with
16C711JW parts as these do not have the internal oscillator and I am not
aware of any other pre-programmed registers that can be erased with the UV.

It will be interesting to see how Microchip will address this issue on the
forthcoming 12F series.

Regards,

Sean

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2002\01\17@090509 by Ted Mawson

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Thanks Sean,

I spoke to MChip yesterday and they matched what you said, the 16C771s
don't have an OSCCAL value and can be erased with no OSCCAL problems.
The guy also told me that MChip are going completely to Flash
programming so this will become a non-issue in time.

Ted Mawson
RemoveMETed.MawsonspamTakeThisOuTPortfolioPM.com
======================================
Sean Alcorn - Avion Sydney wrote...

on 17/1/02 2:50 AM, Ted Mawson at Ted.MawsonEraseMEspam.....PORTFOLIOPM.COM wrote:

> 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
> http://www.microchips.com website returns zilch on a search for 'OSCAL'.

Ted,

As far as I know, the OSCCAL (two Cs) is unique to the 12C, 12CE and
16C505
series chips - ie; the ones that have the internal oscillator. This
value is
written in to the last register in the factory, and the first
instruction is
to move this value into the W register. To use this value, your first
instruction (for these parts) simply needs to be 'OSCCAL' - it is used
to
calibrate the Oscillator.

I could be wrong, but I not think you have anything to worry about with
16C711JW parts as these do not have the internal oscillator and I am not
aware of any other pre-programmed registers that can be erased with the
UV.

It will be interesting to see how Microchip will address this issue on
the
forthcoming 12F series.

Regards,

Sean

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2002\01\17@094349 by Roman Black

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Hi Sean, try setting the calib byte to different
settings and check the clock speed on your cro
or freq meter. If you don't have a freq meter I think
Jaycar sells a multimeter for about $100 AU that
does freq and capacitance and maybe inductance too
if I remember right.

Do the testing in a binary fashion, ie start at 0xC0
to see if you're in the top or bottom half, then
quarter towards the correct side etc. Hope that makes
sense. :o)
-Roman


Sean Alcorn - Avion Sydney wrote:
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2002\01\17@202715 by Dale Botkin

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I have to wonder...  I don't have time to look it up in the data sheet as
I have 300+ PICList messages to read, plus over 2,500 error messages to
deal with thanks to our fine friends and supporters at MIT.  BUT...

I wonder if you could use the internel OSC and get OSC or OSC/4 out from
one of the pins with the right configuration...  then hang a freq. counter
or scope on that pin, figure out how far off you are and try different
OSCCAL values until you were dead on.

Investigation and experimentation left up to the reader...

Dale
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curiosity killed the cat, I say only the cat died nobly."
         - Arnold Edinborough


On Wed, 16 Jan 2002, Rudy Rudy wrote:

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2002\01\17@205843 by Rudy Rudy

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With the 12C509A chip, I don't think you can make the configuration bit so
that you have OSC or OSC/4 out of one of the pins.  What I would suggest is
to write a simple square wave program using one of the pins.  That way, you
can calculate the # of clock cycles it should take, and match that with the
frequency counter (or use the TIMER0 module, I never use it before, so can't
say anything about that).

square_wave    bsf   GPIO, 0
              bcf   GPIO, 0
              goto  square_wave

You should get a not-so-square wave with frequency of OSC/16.  Then, change
the OSCCAL value until you get it dead on (or closest to 'dead on').

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> {Original Message removed}

2002\01\17@214626 by Dale Botkin

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That's work too.  Thought of that after I sent the last one.

Dale
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curiosity killed the cat, I say only the cat died nobly."
         - Arnold Edinborough


On Thu, 17 Jan 2002, Rudy Rudy wrote:

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> > {Original Message removed}

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