My guess would be to look at the bypassing. Don't use too large value bypass
caps or you can make the problem worse (due to track & lead inductance &
resonance effects).
Grounding could also be an issue.
The pulse risetime is the feature to guard against rather than the actual
pulse length.

Richard

> -----Original Message-----
> From: Ben Stragnell [mailto:spare@CODEPUPPIES.COM]
> Sent: Sunday, May 30, 1999 7:52 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Arrrgh! Wish I'd paid more attention in school...
>
>
> Hi,
>
> > Power supply bypassing - if your supply lines are long (1.5
> to 2" can be
> > long when using chips that are very fast) then you should put bypass
> > capacitors (0.1 or 0.01 uF ceramics) on each chip's power
> supply pins.
>
> This seems to be the favourite contender at the moment... I
> need to go out
> and buy some caps by the sound of things. Incidentally, how
> fast is "very
> fast"?... The PIC's drive by a 20MHz clock, but its internal
> instruction
> speed is 5MHz, so the narrowest pulse I'll be delivering to
> any latch or
> other external component is 200ns. Is that sufficient to
> cause problems?
>
> > Ground noise - if your ground line is long and snakes
> around a lot, you
...........etc.