Re: Single ended termination?.
Heikki Saha <[email protected]> Thu, 11 Feb 2021 07:42:17 +0200
| Newsgroups | gmane.comp.hardware.bus.can |
|---|---|
| Message-ID | <CAGCYbHR2c1ZBZ4JVOjtNP_L1piRwrzUJgbSFG0BrRRa3yYFgPg@mail.gmail.com> |
--0000000000008c1c0905bb08fb03 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable [CANLIST] Single ended termination?. Inbox A Al Thomason I have a question for the group: Every one of us has (and likely does) run with a single 120 ohm terminator on the development bench; and all refer... Why is this message in Spam? It's similar to messages that were detected by our spam filters. H Heikki Saha to canlist 2 days ago Details Hello, The purpose of the terminator is to get the end of the transmission line look like an infinitely long line with impedance equal to the line impedance (120ohm with CAN) and thus prevent reflections. Thus, single terminator may be installed into one end, but the another end remains unterminated (infinite impedance), which leads into over- and undershoots. While the communication will pass through, the transmission line is still broken. From practical point of view, the most significant risk is that any other problem more will lead into total black-out. And one shall keep in mind that the physical layer design has a direct effect on the bit error probability, which is a basis for residual error rate, which has further effect on the availability and safety performance of the entire system -- it is easy to violate the system requirements with a poor CAN cabling design. There are some reference designs (published by Daimler) in the literature for centre termination but they cannot be recommended, because each of such networks needs to be intentionally fine tuned. In addition to the clumsy design, such will be a service nightmare. My recommendation is to adopt a standard cabling and connector scheme, where you'll find batch cables, Y- or V-branches and termination plugs, e.g. MiniChange, M12 or Deutsch DT04/06 series. Best regards, On Thursday, February 11, 2021, Russell Shaw <[email protected]> wrote= : > On 11/2/21 8:30 am, Al Thomason wrote: > >> Heinz, >> >> The answer is we have a cabling system with short adapters to allow >> for click-n-go daisy-chaining connecting up the nodes. (And to >> Heikki's point, it is built around DTM connectors in this case, using >> the terminators and Y's which are available). The reality at hand >> is: If all this is short, even with reflections from one >> un-terminated end it does often work. >> >> But (And I want to be clear on this) WE do not support customers who >> want to do this, for all the reasons Heikki mentioned. >> >> Which is why I wanted to check with this group to see if there was >> indeed some legitimate paper, or study that had been done around >> single ended termination of short / low node count installs... I >> have never seen one, but that does not mean there isn't one out there >> <smile> >> >> I can make measurements in the lab, but am not keen on proceeding >> based on only a 1x sample 'In the Lab'. Much different between that >> and when we get 1,000's installed in the field - with age impacting >> things, wires ran with cross coupling, Who knows what can and will be >> done by installers. Which is why I was seeking if there was some >> study, or reference that existed on this specific topic. >> > The thing that matters is the longest round-trip delay time from a node t= o > the unterminated end of the cable. There may be many unterminated ends in= a > star. > > If the fastest rise/fall time of a node is close or longer than any delay > time involving reflections from unterminated ends, then waveform overshoo= t > and distortion will be small. The system will work ok. A good looking > waveform on a cro with smooth non-notchy edges is what is needed. > > The only drawback is a fast rise-time node might be added one day, or the > bit rate increased. > > -- > Subscribe, unscribe, and archives at www.canlist.org - report any > problems to <[email protected]> > --=20 Heikki Saha, CTO M.Sc. Automation Dr.Tech. Electronics TK Engineering Oy Hovioikeudenpuistikko 13 as 3, 65100 Vaasa +358 (0)50 588 6894 email: [email protected] skype: heikki.saha_tke We are also in the 17th iCC: https://www.can-cia.org/icc --0000000000008c1c0905bb08fb03 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <div><br></div><div class=3D"Ls" style=3D"display:block;font-size:13px"><di= v class=3D"As "><div class=3D"Cs"></div></div></div><div id=3D"cv_" class= =3D" Xg " style=3D"width:360px;height:auto;font-size:13px"><div class=3D"Z= g" style=3D"width:360px;overflow-y:auto"><div class=3D"Rg"><div class=3D"Li= "><div class=3D"yj"><div class=3D"Ah oj"><div class=3D"sj"><div id=3D"cvcst= aroff" class=3D"M j b" tabindex=3D"0"><div class=3D"V j um tj b"></div></di= v></div><div class=3D"rj"><span class=3D"qj pj">[CANLIST] Single ended term= ination?.</span><span class=3D"uj"><div class=3D"xj"><span class=3D"Qg vj">= Inbox</span></div></span></div></div><div class=3D"Ph"><div id=3D"cvcmsg_17= 783bed8b2b8fff" class=3D"yh wj" style=3D"background-size:2px 2px;height:70p= x;margin-bottom:0px;overflow:hidden"><div class=3D"Vh" id=3D"cvcfullmsg_177= 83bed8b2b8fff"><div class=3D"M j Zi Mi" tabindex=3D"0"><div class=3D"Zh"></= div><div class=3D"Xh"><div class=3D"Qi"><div class=3D"rh Ri " style=3D"back= ground-color:rgb(91,16,148)">A</div><img class=3D"qh Gh Ri" src=3D"https://= mail.google.com/mail/u/0/photos/thomason.al%40gmail.com?at=3DAF6bupOIao5MXS= HUXM2wLVOyxmM0zdtAOw&sz=3D100&pld=3D1"></div><div class=3D"bj Pg">A= l Thomason</div><div class=3D"cj"><div id=3D"cvcstsnip_17783bed8b2b8fff" cl= ass=3D"Ui Bh"><div class=3D"Vi">I have a question for the group: Every one = of us has (and likely does) run with a single 120 ohm terminator on the dev= elopment bench; and all refer...</div><div class=3D"Wi"></div></div></div><= /div></div><div class=3D"Rj"><div class=3D"ze Wj" style=3D"background-posit= ion:0% 0%;background-size:21px 21px"></div><div class=3D"Tj"><span class=3D= "Vj">Why is this message in Spam?</span>=C2=A0It's similar to messages = that were detected by our spam filters.</div></div><div id=3D"cvcmsgbod_177= 83bed8b2b8fff" class=3D"aj"></div></div></div><div id=3D"cvcmsg_17785573747= ebffd" class=3D"yh " style=3D"margin-bottom:11px;overflow:visible"><div cl= ass=3D"Vh" id=3D"cvcfullmsg_17785573747ebffd"><div class=3D"M j Zi Mi " ta= bindex=3D"0"><div id=3D"cvcreply_17785573747ebffd" class=3D"M j T b hc xh S= " tabindex=3D"0"><div class=3D"V j td" style=3D"background-position:0% 0%= ;background-size:24px 24px"></div></div><div class=3D"Zh"></div><div class= =3D"Xh"><div class=3D"Qi"><div class=3D"rh Ri " style=3D"background-color:r= gb(132,102,0)">H</div><img class=3D"qh Gh Ri" src=3D"https://mail.google.co= m/mail/u/0/photos/me?at=3DAF6bupOIao5MXSHUXM2wLVOyxmM0zdtAOw&sz=3D100&a= mp;pld=3D1"></div><div class=3D"bj Pg">Heikki Saha</div><div class=3D"cj"><= div id=3D"cvcstrecip_17785573747ebffd" class=3D"kj Pg Bh ">to=C2=A0canlist= <br>2 days ago<div id=3D"cvcshowdet_17785573747ebffd" class=3D"M j lj h" ta= bindex=3D"0"><div class=3D"V j nj">Details</div></div></div></div></div></d= iv><div id=3D"cvcmsgbod_17785573747ebffd" class=3D"aj"><div class=3D"Ni"><d= iv class=3D"ni pi " dir=3D"ltr"><div dir=3D"ltr">Hello,<div><br></div><div>= The purpose of the terminator is to get the end of the transmission line lo= ok like an infinitely long line with impedance equal to the line impedance= =C2=A0(120ohm with CAN) and thus prevent reflections. Thus, single terminat= or may be installed into one end, but the another end remains unterminated = (infinite impedance), which leads into over- and undershoots. While the com= munication will pass through, the transmission line is still broken. From p= ractical point of view, the most significant risk is that any other problem= more will lead into total black-out. And one shall keep in mind that the p= hysical layer design has a direct effect on the bit error probability, whic= h is a basis for residual error rate, which has further effect on the avail= ability and safety performance of the entire system -- it is easy to violat= e the system requirements with a poor=C2=A0CAN cabling design.</div><div><b= r></div><div>There are some reference designs (published by Daimler) in the= literature for centre termination but they cannot be recommended, because = each of such networks needs to be intentionally fine tuned. In addition to = the clumsy design, such will be a service nightmare.</div><div><br></div><d= iv>My recommendation is to adopt a standard cabling and connector scheme, w= here you'll find batch cables, Y- or V-branches and termination plugs, = e.g. MiniChange, M12 or Deutsch DT04/06 series.</div><div><br></div><div>Be= st regards,</div></div></div></div></div></div></div></div></div></div></di= v></div></div><br>On Thursday, February 11, 2021, Russell Shaw <<a href= =3D"mailto:[email protected]">[email protected]</a>> wrote:<br= ><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1= px #ccc solid;padding-left:1ex">On 11/2/21 8:30 am, Al Thomason wrote:<br> <blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p= x #ccc solid;padding-left:1ex"> Heinz,<br> <br> The answer is we have a cabling system with short adapters to allow<br> for click-n-go daisy-chaining connecting up the nodes.=C2=A0 (And to<br> Heikki's point, it is built around DTM connectors in this case, using<b= r> the terminators and Y's which are available).=C2=A0 The reality at hand= <br> is:=C2=A0 If all this is short, even with reflections from one<br> un-terminated end it does often work.<br> <br> But (And I want to be clear on this) WE do not support customers who<br> want to do this, for all the reasons Heikki mentioned.<br> <br> Which is why I wanted to check with this group to see if there was<br> indeed some legitimate paper, or study that had been done around<br> single ended termination of short / low node count installs...=C2=A0 =C2=A0= I<br> have never seen one, but that does not mean there isn't one out there<b= r> <smile><br> <br> I can make measurements in the lab, but am not keen on proceeding<br> based on only a 1x sample 'In the Lab'.=C2=A0 Much different betwee= n that<br> and when we get 1,000's installed in the field - with age impacting<br> things, wires ran with cross coupling, Who knows what can and will be<br> done by installers.=C2=A0 Which is why I was seeking if there was some<br> study, or reference that existed on this specific topic.<br> </blockquote> The thing that matters is the longest round-trip delay time from a node to = the unterminated end of the cable. There may be many unterminated ends in a= star.<br> <br> If the fastest rise/fall time of a node is close or longer than any delay t= ime involving reflections from unterminated ends, then waveform overshoot a= nd distortion will be small. The system will work ok. A good looking wavefo= rm on a cro with smooth non-notchy edges is what is needed.<br> <br> The only drawback is a fast rise-time node might be added one day, or the b= it rate increased.<br> <br> --<br> Subscribe, unscribe, and archives at <a href=3D"http://www.canlist.org" tar= get=3D"_blank">www.canlist.org</a> - report any problems to <<a href=3D"= mailto:[email protected]" target=3D"_blank">canlist-owner@= vector-informat<wbr>ik.de</a>><br> </blockquote><br><br>-- <br><div dir=3D"ltr"><div><div dir=3D"ltr"><div><di= v dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr">Heikki Saha, CTO<= br> =C2=A0 M.Sc. Automation<br> =C2=A0 Dr.Tech. Electronics<br> TK Engineering Oy<br><font face=3D"arial, helvetica, sans-serif">Hovioikeud= enpuistikko 13 <span style=3D"color:rgb(51,51,51);font-style:normal;font-we= ight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transf= orm:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,2= 55);float:none;display:inline">as 3</span><span style=3D"color:rgb(51,51,51= );font-style:normal;font-weight:400;letter-spacing:normal;text-align:start;= text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;bac= kground-color:rgb(255,255,255);float:none;display:inline">, 65100 Vaasa</sp= an></font><br> +358 (0)50 588 6894<br> email: <a href=3D"mailto:[email protected]" target=3D"_blank">heikki.saha@= tke.fi</a><br> skype: heikki.saha_tke</div><div dir=3D"ltr"><br><div>We are also in the 17= th iCC: <a href=3D"https://www.can-cia.org/icc" target=3D"_blank">https://w= ww.can-cia.org/icc</a><br></div></div></div></div></div></div></div></div><= /div></div><br> --0000000000008c1c0905bb08fb03-- -- Subscribe, unscribe, and archives at www.canlist.org - report any problems to <[email protected]>