On Tuesday 07 October 2014 09:03:34 Erik Christiansen did opine And Gene did reply: > On 07.10.14 09:14, Gene Heskett wrote: > > But recognizing that clipping is something that generally comes from > > 60+ years of using a scope that can show you that stuff. And that > > is something a logic analyzer simply isn't capable of doing until > > the condition actually forces a repeatable logic mistake. Thats > > maybe .0000001% of the time even in bad designs that should never > > have been shipped to the board house. But its often enough the gear > > will get a reputation as being flaky out in the field. A slower > > scope won't show you that regardless of the maker label on it. > > Fortunately many of these small oscilloscope adaptors have two analogue > channels in addition to 8 or 16 logic analyser channels. If the > analogue channels have enough bandwidth, then they'll sniff out > glitches and ringing, while the logic analyser channels see much less > frequent use, to view timing relationships of a bunch of logic > signals. The ability to trigger (analogue sweep included) on a bit > pattern (with don't cares) on the logic lines, very nifty when you > need it. > > And yes, experience can make a big difference. The scope probes have to > be 100 MHz rated too, not just cheapy stuff. And that 3" lead on the > probe's ground clip can cause ringing that wasn't there, if risetimes > are short. For the tricky measurement above, I'll bet you use a little > bit of tinned wire wrapped around the earth collar, bent to reach the > nearest earth pin on the chip, in extremis.
Yes, and I am bumfuzzled that more probe kits do not include that little detail. I am presently using some 200Mhz rated 10x's on my Hitachi V1065, and they didn't come with that but I've always kept the old bits handy since they seem to fit well on todays crop of probes. OTOH, one gets used to mentally subtracting that from what you do see without it, but that takes lots more practice. But I got that in spades from the 18 years at the tv station too. > And, Viesturs, the little > trimmer capacitor in the side of the probe initially needs to be tuned > to remove false overshoot or undershoot on the trace, while the probe > is held on a clean squarewave "calibration" signal. A good > oscilloscope will include one of them on a pin on the frontpanel. (The > BS325 has one, I read. My old BS310 doesn't.) > > Erik Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Meet PCI DSS 3.0 Compliance Requirements with EventLog Analyzer Achieve PCI DSS 3.0 Compliant Status with Out-of-the-box PCI DSS Reports Are you Audit-Ready for PCI DSS 3.0 Compliance? Download White paper Comply to PCI DSS 3.0 Requirement 10 and 11.5 with EventLog Analyzer http://pubads.g.doubleclick.net/gampad/clk?id=154622311&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
