What programmer were they burned with?

Does it do proper voltage margining on verify?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

----- Original Message -----
From: Tom Phillips <phillipst@CONLOG.CO.ZA>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, September 22, 2000 3:51 AM
Subject: [PIC]:In-situ PIC16F84 configuration bit changes


> 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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