Re: switchable or separate termination in can network

Hello,

The SW-switchable resistors may or will be tricky -- common implementations
switch a resistor into use only, when the device has power on. So, when you
have your system unpowered, typically there is no way to measure, in which
devices the resistors are activated.

The detection is not simpler with the powered system, where you cannot measure
the resistance directly. You can measure the voltage levels, but with three
resistors the network may enter bus-off and you should think about, how it is
reliable to use history data in the detection.

My advice is to use a wiring harness with fixed terminators and just an option
connector for the FMS unit.

Best regards,

-H

Heikki Saha, CTO
  M.Sc. Automation
  Dr.Tech. Electronics
TK Engineering Oy
Mail address:  P.O. box 810, FIN-65101 VAASA
Visit address: Yrittäjänkatu 17, FIN-65380 VAASA
+358 (0)50 588 6894
[email protected]
http://www.tke.fi/
http://www.canopen.fi/

----- Original Message -----
From: "Hadarits Kft." <[email protected]>
To: [email protected]
Sent: Wednesday, June 24, 2015 10:58:08 PM
Subject: [CANLIST] switchable or separate termination in can network

Hi All,

we  install fleet managenet devices in vehicles and sometimes connect its to
the CAN system too. We need to keep the termination value on 120ohm. The
device's installation manual offer to measure (with multimeter) the
resistance between the CANL and CANH wires (without powering the CAN
network; in general switch off the ignition). Depends on the measured value
we have to swith on or off the device's termination resistor.
My question: if the CAN network consists one or two node with switchable
termination resistor at the network's end, will the measurement (without
powering) shows the real network termination resistance? In case it won't
shows the real value, is there any easy way to determine it?  (or I have to
use scope to  evaluete the rise and drop edges?)

Thanks in advance: Tamas Hadarits
www.tachografszerviz.hu





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