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
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