On Saturday 02 December 2017 06:12:21 Frederic RIBLE wrote: > On 2017-12-02 11:24, Gene Heskett wrote: > > I'd have really serious doubts anybody ever considered the > > transmission line termination characteristics needed to preserve a > > perfect square wave anyway. And if I asked that of the guy at Lowes > > spooling off 100 feet of that cable for me, he'd think I was > > suddenly talking in swahili. > > Many MODBUS/RS485 papers are talking about 120 ohms bus termination > and signal reflection effects. > http://www.ti.com/lit/an/slla272c/slla272c.pdf > My VFD has a switch to active this termination on the MODBUS input. > Here is an extended study: > http://support.fccps.cz/download/adv/frr/RS485/RS485.html
Which quotes Steve Ciarcia (circuit cellar) several times. An excellent source of info. We once got into a discussion, many years ago, because of his paper-centric approach to such things, whereas I have an 8th grade "education", but have learned virtually everything I know from encountering it in real life. One of the motto's I have practiced for probably 65+ years is that I will fix something to factory specs twice. The third time it fails at the same part, probably for the same reason, I'll find that reason and fix it right. Steve's final reply in that discussion was that "the most important sheepskin was the one we slept on". I really had to chuckle on that one. That magazine, a subscription to it, was one of the freebies I always demanded as a condition of my employment, that and McGraw-Hills "Electronics". And an occasional article from Bob Pease, whom I once called at National Semi to talk about something, and who's fondness for a VW Beatle finally killed him. And of course throw in Ed Nissle (spelling?) as an Honorable Mention. Anyway, we'll see if it needs terminations to function correctly, possibly before the day is done. I suspect the single ended portion will benefit from a 75 ohm or so source termination. With only a gigahertz scope, I would expect things to settle quickly on 4 feet of no-name shielded cable to the bob, and who knows that the 25 wire ribbon looks like. With this bob, as in most, gaining access with a scope probe is not easy. So you put a signal in, and scan the pins of the ic's on the bob looking for it. > However, I do not know if that is really important for the particular > case of a spindle encoder. > > > Just another of my war stories from 40 years in broadcast > > engineering. :) > > I was sure that will recall nice stories about radio ;-) > Thanks. > Frederic (callsign F1OAT) > http://cnc.f1oat.org Thanks Frederic. Les suggested some simplifications to my hal file, and that of course will take some time. 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
