William Chops Westfield wrote:
> On Mar 6, 2007, at 1:38 AM, Alan B. Pearce wrote:
> 
>> So the data sheet is correct, and you are trying to
>> operate the chip outside the limits.
> 
> I dunno.  If the chip behavior has changed and the datasheet
> HASN'T changed, that seems like a microchip-side problem to me.
> The inability to adequately clamp inputs with ordinary silicon
> diodes seems like a pretty serious issue. 

The PIC chip itself is made from, as you call it, "ordinary silicon" 
Bill.  Adding an external "ordinary silicon" clamp diode simply puts two 
  "ordinary silicon" diodes in parallel.

Which one will turn on first?

Flip a coin. In fact, since the PIC is powered up and dissipating energy 
as heat, it will be (likely) warmer and have a lower Vf than the 
external one so the external one will tend not to help.

Schottky clamps are "de rigeur" for clamping SILICON microcontrollers.




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