Hi Shane, we manufacture PIC based products too.
We use a 20MHz rated PIC at 16MHz to allow safe
overhead. We sounce/sink maximum current <5mA
total from PIC output pins to reduce PIC die
heating and thermal stresses. All inputs and
outputs are slew rate limited and clamped by
5.1v zener diodes, AC spike regulated by RC
networks. All components are rated for 8x the
heat dissipation they actually get.

And we haven't had a product failure either.
I don't mean to be harsh, but when you talk
about real world experience my real world
experience tells me to use generous ratings
overheads. I respect safty margins in designs
like I respect a good driver that allows
safety margins on the road. Yes, you can miss
hitting the other car by 1 inch and be within
spec. I would rather miss it by a good safe
margin. Sounds like you don't mind hitting
the other car if you don't get whiplash?? ;o)
-Roman




Shane Tolmie wrote:
>
> Hi,
>
> We design and manufacture PIC based units.  We have sold just over 1k of units over the past 12 months.   We buy all our chips in at
> 4Mhz, because they are easier to get hold of.  Now, as everyone knows, 20Mhz and 4Mhz chips are made from the same die.  We run
> chips labelled 4Mhz at 16Mhz, and we have never had any problems at all.
>
> Conclusion: running 4Mhz chips at 16Mhz is fine.  This is based on real world experience, not hearsay or witch hunting.

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