I might be totally off base here but do you have adequate decoupling=20
capacitors on the power pins as close to the PIC as possible ?

Most issues I've had with startup instability have been due to inadequate o=
r=20
(once) faulty decoupling capacitors.

Dom
----- Original Message -----=20
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


>I have just created a simple application using the 8Mhz internal oscillato=
r
> of a PIC18F2520.  The problem is that about half the time the oscillator
> 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 after=
=20
> the
> power supply has already stabilized, so I inferred that it was the slow=20
> rise
> rate of the analog supply that was causing the problem.  However, it look=
s
> like I am getting 0 to 5V at the PIC Vdd pin in about 20 ms, which seems=
=20
> 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 enabled =
/
> disabled, Brown-Out-Detect enabled / disabled, etc. but that doesn't seem=
=20
> to
> make any difference.  The hardware is extremely simple, so I must be=20
> missing
> something in the firmware.  Any suggestions for where I might look would=
=20
> be
> much appreciated.  Thanks,  Foster
>
> --=20
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> http://mailman.mit.edu/mailman/listinfo/piclist
>=20

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