If it's a problem of static field (and not an output which in real
life is input ) then probably you should check if thre is any ground
plane below the PIC belly which is left floated and not connected to
GND (if there is any). I had once this problem, but with a SMD
package. I hope your prototype is on a proffesional PCB before running
in the field...

Vasile

On 9/23/09, Quintin Beukes <quintin@last.za.net> wrote:
> That was actually what we tried RIGHT before finding the solution.
> Doing the 10k resistor between VDD and MCLR didn't help for being
> reset by static fields. And when only the PORTB output pins are
> grounded, then it takes the problem away.
>
> Quintin Beukes
>
>
>
> On Wed, Sep 23, 2009 at 6:10 PM, Dwayne Reid <dwayner@planet.eon.net> wrote:
> > At 11:32 AM 9/22/2009, Quintin Beukes wrote:
> >
> >>Maybe it's not connected to an LED. I'm not sure. Though I know that
> >>it is configured as either an INPUT/OUTPUT.
> >
> > I've just read your most recent message, where you say that MCLR is
> > used as a programming pin.
> >
> > I guess my question would be: is there a pull-up or pull-down
> > resistor on that pin?
> >
> > The reason that is important is this: even if MCLR is configured as
> > an input, it can still have an effect on the PIC,  The reason is that
> > MCLR is responsive to 3 different voltage levels: Gnd, 5V, Vpp.  If
> > MCLR is just floating, it is possible that an external static field
> > can drive MCLR well above 5V and into the Vpp territory.  The PIC
> > will do decidedly strange things when that happens - most often, it
> > will attempt to go into programming mode.  But the effect is
> > different with different PIC families.
> >
> > My suggestion, for what its worth, would be to examine the PCB and
> > see what is connected to MCLR.  If it is just floating, tie a 10K
> > resistor between MCLR and Vdd.  You may now find that your problems
> > have vanished.
> >
> > dwayne
> >
> >
> > --
> > Dwayne Reid   <dwayner@planet.eon.net>
> > Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> > (780) 489-3199 voice          (780) 487-6397 fax
> > www.trinity-electronics.com
> > Custom Electronics Design and Manufacturing
> >
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist