At 12:45 PM 23/09/2009, you 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


You should not ground outputs directly, IMHO, ever. There is no way that
an output would cause the symptoms you describe (barring extreme conditions
such as very high EMI in the vicinity from a substantial RF 
transmitter, welder etc.).

Most likely, there is a floating input somewhere in your system that is
triggering the reset either directly or via an interrupt. There are several
interrupt pins on PORTB.

At this point you should not be trusting anything- verify that the pins
are actually outputs by verifying that they will actually sink or source
current (eg. to an LED in series with a resistor to Vdd or Vss).
You could also try feeding a ~10Hz 0V/5V square wave signal into each "output"
via a 1K series resistor and see if any misbehavior is noted.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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