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.