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PICList Thread
'OSCCAL and UV erase'
1997\08\28@111204 by Lawrence Lile

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PIC-nikkers:

What happens to the OSCCAL number when you UV erase a windowed
PIC12C508?  Is the OSCCAL even programmed into windowed parts in the
first place?     I've noticed that piezo beepers hooked up to two
different windowed parts usually have different tones, meaning the
oscillators must run at different freq's.


-- Lawrence Lile

Download AutoCad blocks for electrical drafting at:
http://members.sockets.net/~llile/index.htm

1997\08\28@114657 by Kalle Pihlajasaari

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Hi Lawrence,

> What happens to the OSCCAL number when you UV erase a windowed

Get erased.

> PIC12C508?  Is the OSCCAL even programmed into windowed parts in the
> first place?     I've noticed that piezo beepers hooked up to two

Yes.

> different windowed parts usually have different tones, meaning the
> oscillators must run at different freq's.

Trimmed frequency is still out by 1.2 % max and untrimmed by 10%

Beating could be heard in trimmed devices, absolute difference
on two untrimmed devices if you have a good ear.

Check out my link below that describes very simple program
to recover a lost OSCCAL value from a 12C50x/JW device.

If you are not fussy select 7 as the OSCcal value.  The median is
there so you will minimise bulk error.

  http://www.ip.co.za/people/kalle/pic/default.htm#caltest

Cheers
--
Kalle Pihlajasaari   spam_OUTkalleTakeThisOuTspamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer

1997\08\28@122508 by Mike Keitz

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On Thu, 28 Aug 1997 09:56:55 +0000 Lawrence Lile <.....lilelKILLspamspam@spam@TOASTMASTER.COM>
writes:
>PIC-nikkers:
>
>What happens to the OSCCAL number when you UV erase a windowed
>PIC12C508?  Is the OSCCAL even programmed into windowed parts in the
>first place?

It is erased.  The cal value is merely a MOVLW instruction in the highest
program address.  (The MPLAB/PICSTART software doesn't allow storing an
instruction there, but physically the EPROM is continuous.) After a
reset, the 12-bit core sets the PC to all ones, which causes the MOVLW
<cal value> to be exectuted first.  The PC then rolls over to all zeros,
where the first user instruction is stored.  Without the cal value
instruction, the W register would be undefined after reset, so assuming
it has a cal value will cause unpredicatble results.

As part of the manufacturing process, the factory determines the correct
value and programs it into the EPROM, leaving the rest of the EPROM blank
just as if it were a plastic chip.  Everything about a window chip is
exactly the same as an OTP one except the package, and additional testing
so it is qualified for all oscillator settings.

Before erasing the chip the first time, read the factory's value out and
remember it for future reprogrammings.

1997\08\28@124234 by Martin R. Green

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If I remember my initial reading of 12C5XX app notes, you should save the
OSCCAL value by reading it with your programmer BEFORE you erase it.  When
you reprogram the device, reprogram the old OSCCAL value with it.


CIAO - Martin R. Green
elimarspamKILLspambigfoot.com

----------
From:   Lawrence Lile[SMTP:.....lilelKILLspamspam.....TOASTMASTER.COM]
Sent:   Thursday, August 28, 1997 5:56 AM
To:     EraseMEPICLISTspam_OUTspamTakeThisOuTmitvma.mit.edu
Subject:        OSCCAL and UV erase

PIC-nikkers:

What happens to the OSCCAL number when you UV erase a windowed
PIC12C508?  Is the OSCCAL even programmed into windowed parts in the
first place?     I've noticed that piezo beepers hooked up to two
different windowed parts usually have different tones, meaning the
oscillators must run at different freq's.


-- Lawrence Lile

Download AutoCad blocks for electrical drafting at:
http://members.sockets.net/~llile/index.htm

1997\08\28@125209 by Shane Nelson

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On Thu, 28 Aug 1997, Lawrence Lile wrote:

> PIC-nikkers:
>
> What happens to the OSCCAL number when you UV erase a windowed
> PIC12C508?  Is the OSCCAL even programmed into windowed parts in the
> first place?     I've noticed that piezo beepers hooked up to two
> different windowed parts usually have different tones, meaning the
> oscillators must run at different freq's.
>
>

I remember reaading something about calibration #'s being erased
when you erase UV. You're supposed to read the chip first, write
down the calib #, then when you program it re-program the # into
the correct location.

Don't quote me though, that's from memory...

-Shane.

1997\08\28@135432 by mike

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In message  <14595958302111spamspam_OUTtoastmaster.com> @spam@PICLISTKILLspamspamMITVMA.MIT.EDU writes:
> PIC-nikkers:
>
> What happens to the OSCCAL number when you UV erase a windowed
> PIC12C508?  Is the OSCCAL even programmed into windowed parts in the
> first place?     I've noticed that piezo beepers hooked up to two
> different windowed parts usually have different tones, meaning the
> oscillators must run at different freq's.
>
>

The osccal is there when you first get the PIC, but is erased
along with all the program code when exposed to UV.

The thing to do is read the value before you erase for the first time
and scratch it on the gold top or underneath.

Even with the osccal set properly, I would think you would get
different tones from your beepers as the internal oscillator is
only an RC type with sizeable variations in frequency part to
part due to manufacturing process variations etc.

Regards,

Mike Watson

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