Be careful. I don't entirely trust the initialisation of the option and
other registers at power up. This seems to lead to erratic behaviour.
Try initialising them - also make sure the chip is not exposed to light
- the JW version will behave erratically under these circumstances.

> ----------
> From:
> tekatcha@FALLEN.PROVCOMM.NET[SMTP:tekatcha@FALLEN.PROVCOMM.NET]
> Reply To:     pic microcontroller discussion list
> Sent:         Tuesday, November 25, 1997 5:04 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      12C508 @3V oscillator doesn't
>
> I've got a 12C508 JW device to work fine with an internal oscillator
> at 5V
> but at 3V it rarely starts up.
>
> I put a test block of code which just oscillates a pin voltage right
> at
> the beginning of memory. Sometimes the unit will start and sometimes
> it
> will start for a few milliseconds then fail.
>
> I changed the calibration value from 30 to FF and it starts all the
> time
> now, I have another unit that has a calibration value of 40 and it is
> intermittent even after changing the calibration value to ff.
>
> Is there something that I might be doing wrong or should I be using an
> external clock?
>
> Anthony Tekatch
>
> tekatcha@pop.ghbbs.com
>