Thank you Dom.  The 100 nF decoupling cap on this board was almost
half-an-inch from the pins.  Soldered another one across the pins on the
back of the board, and it now starts every time.  (It's a one-off so the
extra cap is a perfectly fine solution.)  Thanks again!

And thank you, Joe.  I didn't try your suggestion, but that's just the kind
of thing I was wondering about.  Seems like good practice, and I may just
implement it anyway.=20

  Foster
=20

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Picbits Sales
> Sent: Wednesday, February 23, 2011 2:06 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] Internal Oscillator doesn't start reliably
>=20
> I might be totally off base here but do you have adequate decoupling
> capacitors on the power pins as close to the PIC as possible ?
>=20
> Most issues I've had with startup instability have been due to inadequate
> or
> (once) faulty decoupling capacitors.
>=20
> Dom
> ----- Original Message -----
> From: "adastra" <foster@adastran.com>
> To: "'Microcontroller discussion list - Public.'" <piclist@mit.edu>
> Sent: Wednesday, February 23, 2011 7:19 PM
> Subject: [PIC] Internal Oscillator doesn't start reliably
>=20
>=20
> >I have just created a simple application using the 8Mhz internal
> oscillator
> > of a PIC18F2520.  The problem is that about half the time the oscillato=
r
> > doesn't start on power up.  I am required to use an existing analog 12V
> > power supply ahead of a 78L05 regulator.  I have discovered that the
> > oscillator will start every time if I connect the 12V to the board afte=
r
> > the
> > power supply has already stabilized, so I inferred that it was the slow
> > rise
> > rate of the analog supply that was causing the problem.  However, it
> looks
> > like I am getting 0 to 5V at the PIC Vdd pin in about 20 ms, which seem=
s
> > to
> > be well within the minimum rise rate spec of 0.05 V/ms.  I have tried
> > various combinations of Configuration bits, i.e., Power-Up-Timer enable=
d
> /
> > disabled, Brown-Out-Detect enabled / disabled, etc. but that doesn't
> seem
> > to
> > make any difference.  The hardware is extremely simple, so I must be
> > missing
> > something in the firmware.  Any suggestions for where I might look woul=
d
> > be
> > much appreciated.  Thanks,  Foster
> >
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>=20
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist


--=20
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