RE: Single ended termination

"John Dammeyer" <[email protected]> Thu, 11 Feb 2021 00:23:01 -0800
Newsgroups gmane.comp.hardware.bus.can
Message-ID <[email protected]> 
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Heikki,
Your message did come through as did a number of others a day after I first=
 posted mine.
=20
I've also noticed and reported that the www.canlist.org  site is considered=
 dangerous by several browsers.  Something about a security certificate.
=20
Back around 2011, TI's Steve Corrigan had retired and he and I had started =
looking into cable behaviour on CAN messages.  I'd sent him some surplus Th=
ick DeviceNet cable for some experiments.  However he unfortunately passed =
before we had much of a chance to do anything with that.  Never really got =
back to it.  He really was the expert on this bus.
=20
Since then most of my CAN systems have had no more than about 10 nodes and =
there are some rules broken.  Mostly on stub lengths.  It's a difficult bat=
tle with mechanical engineers who don't understand that 50 ohm cable is dif=
ferent from 120 ohm cable.  Especially when the thin 50 ohm fits so well an=
d bends so easily. =20
=20
This summer or fall I hope to get back into some really long CAN bus networ=
ks at slower bus rates.  Maybe 100kbps for garden lighting and security.  S=
uch as system may not use 120 ohm cable for everything just to do some test=
ing.
=20
John Dammeyer
=20
=20
=20
From: [email protected] [mailto:canlist-owner@vector-info=
rmatik.com] On Behalf Of Heikki Saha
Sent: February-11-21 12:08 AM
To: [email protected]
Subject: [CANLIST] Single ended termination
=20
Hello,
=20
Had problems getting this through, John already provided nice scope screens=
hot as an example.
=20
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 =
(120ohm with CAN) and thus prevent reflections. Thus, single terminator may=
 be installed into one end, but the another end remains unterminated (infin=
ite impedance), which leads into over- and undershoots. While the communica=
tion will pass through, the transmission line is still broken. From practic=
al 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 physica=
l 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 availabilit=
y and safety performance of the entire system -- it is easy to violate the =
system requirements with a poor CAN cabling design.
=20
There are some reference designs (published by Daimler) in the literature f=
or centre termination but they cannot be recommended, because each of such =
networks needs to be intentionally fine tuned. In addition to the clumsy de=
sign, such will be a service nightmare.
=20
My recommendation is to adopt a standard cabling and connector scheme, wher=
e you'll find batch cables, Y- or V-branches and termination plugs, e.g. Mi=
niChange, M12 or Deutsch DT04/06 series.
=20
Best regards,
=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
=20
We are also in the 17th iCC: https://www.can-cia.org/icc

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</o:shapelayout></xml><![endif]--></head><body lang=3DEN-CA link=3Dblue vli=
nk=3Dpurple style=3D'tab-interval:36.0pt'><div class=3DWordSection1><p clas=
s=3DMsoNormal><span style=3D'font-size:11.0pt;color:#1F497D'>Heikki,<o:p></=
o:p></span></p><p class=3DMsoNormal><span style=3D'font-size:11.0pt;color:#=
1F497D'>Your message did come through as did a number of others a day after=
 I first posted mine.<o:p></o:p></span></p><p class=3DMsoNormal><span style=
=3D'font-size:11.0pt;color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3D=
MsoNormal><span style=3D'font-size:11.0pt;color:#1F497D'>I've also noticed =
and reported that the </span><a href=3D"http://www.canlist.org">www.canlist=
.org</a> <span style=3D'font-size:11.0pt;color:#1F497D'><span style=3D'mso-=
spacerun:yes'>=C2=A0</span>site is considered dangerous by several browsers=
.<span style=3D'mso-spacerun:yes'>=C2=A0 </span>Something about a security =
certificate.<o:p></o:p></span></p><p class=3DMsoNormal><span style=3D'font-=
size:11.0pt;color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal=
><span style=3D'font-size:11.0pt;color:#1F497D'>Back around 2011, TI's Stev=
e Corrigan had retired and he and I had started looking into cable behaviou=
r on CAN messages. <span style=3D'mso-spacerun:yes'>=C2=A0</span>I'd sent h=
im some surplus Thick <span class=3DSpellE>DeviceNet</span> cable for some =
experiments.<span style=3D'mso-spacerun:yes'>=C2=A0 </span>However he unfor=
tunately passed before we had much of a chance to do anything with that.<sp=
an style=3D'mso-spacerun:yes'>=C2=A0 </span>Never really got back to it.<sp=
an style=3D'mso-spacerun:yes'>=C2=A0 </span>He really was the expert on thi=
s bus.<o:p></o:p></span></p><p class=3DMsoNormal><span style=3D'font-size:1=
1.0pt;color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span=
 style=3D'font-size:11.0pt;color:#1F497D'>Since then most of my CAN systems=
 have had no more than about 10 nodes and there are some rules broken.<span=
 style=3D'mso-spacerun:yes'>=C2=A0 </span>Mostly on stub lengths.<span styl=
e=3D'mso-spacerun:yes'>=C2=A0 </span>It's a difficult battle with mechanica=
l engineers who don't understand that 50 ohm cable is different from 120 oh=
m cable.<span style=3D'mso-spacerun:yes'>=C2=A0 </span>Especially when the =
thin 50 ohm fits so well and bends so easily.<span style=3D'mso-spacerun:ye=
s'>=C2=A0 </span><o:p></o:p></span></p><p class=3DMsoNormal><span style=3D'=
font-size:11.0pt;color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoN=
ormal><span style=3D'font-size:11.0pt;color:#1F497D'>This summer or fall I =
hope to get back into some really long CAN bus networks at slower bus rates=
.<span style=3D'mso-spacerun:yes'>=C2=A0 </span>Maybe 100kbps for garden li=
ghting and security.<span style=3D'mso-spacerun:yes'>=C2=A0 </span>Such as =
system may not use 120 ohm cable for everything just to do some testing.<o:=
p></o:p></span></p><p class=3DMsoNormal><span style=3D'font-size:11.0pt;col=
or:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span style=3D=
'font-size:11.0pt;color:#1F497D'>John Dammeyer<o:p></o:p></span></p><p clas=
s=3DMsoNormal><span style=3D'font-size:11.0pt;color:#1F497D'><o:p>&nbsp;</o=
:p></span></p><p class=3DMsoNormal><span style=3D'font-size:11.0pt;color:#1=
F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span style=3D'font=
-size:11.0pt;color:#1F497D'><o:p>&nbsp;</o:p></span></p><div style=3D'borde=
r:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div st=
yle=3D'border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm=
'><p class=3DMsoNormal><b><span lang=3DEN-US style=3D'font-size:10.0pt;font=
-family:"Tahoma","sans-serif";mso-fareast-font-family:"Times New Roman";mso=
-ansi-language:EN-US'>From:</span></b><span lang=3DEN-US style=3D'font-size=
:10.0pt;font-family:"Tahoma","sans-serif";mso-fareast-font-family:"Times Ne=
w Roman";mso-ansi-language:EN-US'> [email protected] [mai=
lto:[email protected]] <b>On Behalf Of </b>Heikki Saha<br=
><b>Sent:</b> February-11-21 12:08 AM<br><b>To:</b> canlist@vector-informat=
ik.de<br><b>Subject:</b> [CANLIST] Single ended termination<o:p></o:p></spa=
n></p></div></div><p class=3DMsoNormal><o:p>&nbsp;</o:p></p><div><p class=
=3DMsoNormal><span style=3D'font-size:10.0pt'>Hello,</span><o:p></o:p></p><=
div><p class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p class=3DMsoNorm=
al>Had problems getting this through, John already provided nice scope scre=
enshot as an example.<o:p></o:p></p><div><p class=3DMsoNormal><span style=
=3D'font-size:10.0pt'><o:p>&nbsp;</o:p></span></p></div><div><p class=3DMso=
Normal><span style=3D'font-size:10.0pt'>The purpose of the terminator is to=
 get the end of the transmission line look like an infinitely long line wit=
h impedance equal to the line impedance&nbsp;(120ohm with CAN) and thus pre=
vent reflections. Thus, single terminator may be installed into one end, bu=
t the another end remains unterminated (infinite impedance), which leads in=
to over- and undershoots. While the communication will pass through, the tr=
ansmission line is still broken. From practical point of view, the most sig=
nificant 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 ef=
fect on the bit error probability, which is a basis for residual error rate=
, which has further effect on the availability and safety performance of th=
e entire system -- it is easy to violate the system requirements with a poo=
r&nbsp;CAN cabling design.<o:p></o:p></span></p></div><div><p class=3DMsoNo=
rmal><span style=3D'font-size:10.0pt'><o:p>&nbsp;</o:p></span></p></div><di=
v><p class=3DMsoNormal><span style=3D'font-size:10.0pt'>There are some refe=
rence designs (published by Daimler) in the literature for centre terminati=
on but they cannot be recommended, because each of such networks needs to b=
e intentionally fine tuned. In addition to the clumsy design, such will be =
a service nightmare.<o:p></o:p></span></p></div><div><p class=3DMsoNormal><=
span style=3D'font-size:10.0pt'><o:p>&nbsp;</o:p></span></p></div><div><p c=
lass=3DMsoNormal><span style=3D'font-size:10.0pt'>My recommendation is to a=
dopt a standard cabling and connector scheme, where you'll find batch cable=
s, Y- or V-branches and termination plugs, e.g. MiniChange, M12 or Deutsch =
DT04/06 series.<o:p></o:p></span></p></div><div><p class=3DMsoNormal><span =
style=3D'font-size:10.0pt'><o:p>&nbsp;</o:p></span></p></div><div><p class=
=3DMsoNormal><span style=3D'font-size:10.0pt'>Best regards,<o:p></o:p></spa=
n></p></div><div><p class=3DMsoNormal><span style=3D'font-size:10.0pt'><o:p=
>&nbsp;</o:p></span></p></div><div><div><div><div><div><div><div><div><div>=
<div><div><p class=3DMsoNormal>Heikki Saha, CTO<br>&nbsp; M.Sc. Automation<=
br>&nbsp; Dr.Tech. Electronics<br>TK Engineering Oy<br><span style=3D'font-=
family:"Arial","sans-serif"'>Hovioikeudenpuistikko 13 <span style=3D'color:=
#333333;background:white'>as 3, 65100 Vaasa</span></span><br>+358 (0)50 588=
 6894<br>email: <a href=3D"mailto:[email protected]" target=3D"_blank">hei=
[email protected]</a><br>skype: heikki.saha_tke<o:p></o:p></p></div><div><p c=
lass=3DMsoNormal><o:p>&nbsp;</o:p></p><div><p class=3DMsoNormal>We are also=
 in the 17th iCC: <a href=3D"https://www.can-cia.org/icc" target=3D"_blank"=
>https://www.can-cia.org/icc</a><o:p></o:p></p></div></div></div></div></di=
v></div></div></div></div></div></div></div></div></div></div></div></body>=
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