Yes, it can be updated anywhere in your program.  But, don't forget to
use a MOVWF OSCCAL at the very beginning of your program (@ address 0)
to establish the proper factory calibration (the data sheet explains
this).  It sounds like you are definitely experiencing a reset problem.
The brown-out circuit may be your only choice.

-Chuck Mauro

> -----Original Message-----
> From: Calvin [SMTP:tgo@CHIH1.TELMEX.NET.MX]
> Sent: Thursday, February 26, 1998 3:27 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Oscilator calibration rewriting...
>
> Does anybody know if the internal oscilator calibration for a 12C5XX
> can be
> restablished (rewritten) from inside a program, and not just at
> StartUp?
>
> I am having a problem when starting up the PIC, this value seem to be
> corrupted sometimes. I have a timed signal coming out of one pin, and
> the
> period of the signal varies if I switch the supply on and off fast.
>
> I don't want to use an external reset circuit or a brown-out circuit
> due to
> cost and limited board space.
>
> TIA
>
> Gabriel Gonzalez
> TGO Electronics