Re: Input to a PIC which goes outside the supply rails
- From: Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 12 Dec 2007 17:35:56 -0800
Joel Koltner wrote:
"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message news:Wf%7j.3833$Vq.2022@xxxxxxxxxxxxxxxxxxxxxxxI probed the oscillator, the probe capacitance stopped it ... phssst ... BANG!
One wonders how many chips they blew up while debugging...
That sort of system is about as far from "fail safe" as you can get!
Yeah. Sometimes people call me the master of penny pinching when I present at a design review but this module topped it all. I mean, they even skimped on the zener. That takes guts. Those modules were actually quite reliable as long as you didn't stop the oscillator. The bypass cap was not too large and not too small, just enough to tide it through the reset without VCC exceeding the limit. But under no circumstances could it go into reset after power-up, ever. A real case of white-knuckle engineering.
--
Regards, Joerg
http://www.analogconsultants.com/
.
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