At 09:51 AM 22/09/00 +0200, you wrote:

I have heard of a similar occurrence. It happened when the engineers sprayed
the PCB with a protective lacquer. The 16C84s reprogrammed themselves because
of the static charge on the MCLR pin caused by the spray put the '84 into
program mode.

The problem was fixed when a resistor was used to bleed any static built-up
of the MCLR pin.

I cannot say if this is the same problem you have but it might provide a
clue of some sort.

-Jim


>Help
>
>I have PIC16F84 -04I/SO controllers changing their configuration bits on the
>fly.  Some have been installed for a few weeks, others have been in the
>field for two years. The circuits are potted and therefore I can rule out
>any tampering.
>
>Environment : 14 to 21V DC, temperature range -8 deg Celsius to +80 deg
>Celsius, outdoors
>Oscillator : Murata CSTCS 4.00MHz (integrated 18pF caps)
>Original Configuration : OSC=XT, WDT=ON, PUT=ON, CP=ON
>Supply : 78DS05F 5V regulator designed for automotive industry
>Voltage supervisor : Motorola MC33064
>Source Power-Up : Very slow rise & fall from 0V DC to 19V DC (sometimes in
>the region of 20 minutes).
>
>The reset circuitry has been designed such that the circuit draws more
>current in reset than when operational, this stops the supervisory chip
>hunting in and out of reset.
>
>Failed units' configuration bits are generally as follows; OSC=RC, WDT=ON,
>PUT=OFF, CP=OFF
>
>I have also found that we can get some failed units to run normally by
>powering them up quickly (normal 5V DC supply).
>
>Applying a 4MHz oscillator to pin 16 (OSC1) shows the device is still
>operational, just that the on board oscillator will not function with the
>OSC configuration bit set to RC.
>
>Has anyone come across something similar, or can anyone suggest reasons for
>this anomaly?
>
>Regards
>
>Mr Tom Phillips
>Systems Engineer (Solar)
>Merlin Gerin SA (Pty) Ltd t/a CONLOG
>Tel       :   +27-31-268-1111 (S/Board)
>              +27-31-268-1476 (Direct)
>Fax       :   +27-31-208-7790
>e-mail    :  phillipst@conlog.co.za
>Internet  : www.conlog.co.za
>
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>
Regards,

Jim Robertson
NEWFOUND ELECTRONICS
Email: newfound@pipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.

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