The echo problem is only relevant for the highest baudrates, where the length of the cable
and the propagation time is in the same order of magnitude as a baud time. If you run a CAN at 250 kHz it will run on any cable. Notice that the susceptibility for high frequencies may suffer ! Gert Van: [email protected] [mailto:[email protected]] Namens Cortland Richmond Verzonden: dinsdag 24 januari 2012 20:18 Aan: '[email protected]' Onderwerp: Re: 120 ohm CAN cable Gary, Any reflections that unacceptably degrade the CAN signal must be avoided, which is the reason for terminations. Network cables usually run 105 Ohms or so and reflections from cable-to-load will at 120 Ohms be relatively low-level. You can probably DEMONSTRATE there's no need for better by actually setting up the requisite length of cable as installed and looking at BER and waveforms. That may be faster and cheaper than calling for outside analysis. Cortland Richmond On 1/24/2012 1347, McInturff, Gary wrote: Thanks, that is exactly what I keep trying to tell them, unsuccessfully for the moment, and wanted to check my facts. Gary From: Rob Kado [mailto:[email protected]] Sent: Tuesday, January 24, 2012 10:42 AM To: McInturff, Gary; '[email protected]' Subject: RE: 120 ohm CAN cable The cable itself does not need to be 120 Ohms; it is the resistor across CAN High to Low at the end. Rob Kado Manager & Sr Technical Specialist Electromagnetic Compatibility Chrysler 800 Chrysler Drive CIMS 481-47-20 Auburn Hills, MI 48326 Desk: (248) 576-6915 Mobile: (248) 467-0639 Fax: (248) 576-7045 From: [email protected] [mailto:[email protected]] On Behalf Of McInturff, Gary Sent: Tuesday, January 24, 2012 1:16 PM To: '[email protected]' Subject: 120 ohm CAN cable Can bus requires a 120 termination, and I have a client that is trying to do it with the bare cable, and I don't know that such cable exists unless custom built. I'm aware of impedance controlled coax but this is just your standard hookup cable in an appropriate jacket. We terminate the line at each end but don't control the cable itself. Yes there will be reflections but as I understand it the CAN standard identifies the termination requirements but doesn't identify a specific 120 ohm cable between the terminating resistors. Comments please? Gary McInturff Reliability/Compliance Engineer - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
