The protection diodes on each pin will make them low impedance to high
voltage ESD. The goal with ESD is to provide enough resistance that the
current is forced through another (lower impedance) path to ground.

This will be difficult with the entire PIC accessible. No matter what
protection method you choose, it could be easily circumvented when ESD is
applied directly to the pin.

You might try using a zener on each pin, but these are usually too slow.
Spark gaps may also be effective.

David
 

> -----Original Message-----
> From: wouter van ooijen [mailto:wouter@voti.nl] 
> Sent: Sunday, February 17, 2008 11:34 AM
> To: 'Microcontroller discussion list - Public.'
> Subject: RE: [PIC]
> 
> > > Are you sure? That does not seem logical to me.
> > 
> > Why not logical? A series resistor can help protect the MCU 
> > quite effectively. 
> 
> In my head I model ESD as a small C capacitor charged to a large
> voltage, suddenly placed over two (randomly chosen) IC pins. High
> voltage means that a series resistor has very little influence on the
> voltage caused internally, unless an internal low-impedance 
> path (to the
> other pin) exists. Cmos == high input impedance == no such path? 
> 
> Wouter van Ooijen
> 
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
> consultancy, development, PICmicro products
> docent Hogeschool van Utrecht: www.voti.nl/hvu
>  
>  
> 
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