Roman,

could you please explain in a little more detail why the
47K resistor works in this instance?  at this point im scared
of any high voltage, even at really low current, hitting the
5v rail.  while andy did get the diode the wrong way around,
and i was going to tell him to turn it around, i would
welcome an argument for using a resistor instead.  i can
think of one reason, that when using 3V the diode drop might
interfere with sensing a high on the MCLR line.  do you have
any others?

thanks,
alice



> Andy N1YEW wrote:
> >
> > what direction i forgot offhand lol
> >
> > i think like this
> >
> > 5v rail ----|<1---- mclr
> >
> > right?
> >
> > andy
>
> Very wrong! Forget the diode and use a 47k resistor.
> When you mentioned you connected MCLR with a 1.6k resistor,
> then connected it to 13v but the pin only rose to 10.95v
> it seems like the MCLR pin was connected to something else,
> as it is high impedance and would have been 13v with very
> little current. I am guessing that you had the MCLR pin
> connected to the main Vdd (5v) power pin, so you were
> actually trying to force 13v into the 5v power pin.
> This would cause all the symptoms you mentioned and
> explain why it killed the chips.
>
> So;
> * use a 47k resistor betweeen Vdd pin and MCLR pin
> * use a 470 ohm resistor for 13v to MCLR
> * it will then be safe and not blow chips. :o)
>
> -Roman
>
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