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Canbus strange behaviour.

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(@angelo)
Posts: 31
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Topic starter
 

Hi, I am playing with the canbus setup, in the lab, before installing everything in the dyno room.

I have a 40 meters cable, with 120ohms impedance. I use it on a railway machine, both for ethernet and RS-485 without problems.

Yes, I know, I know, 40 meters for canbus is very long, but it should work. In the dyno room, the cable will be around 10 meters.

 

In the lab, the config is: Ultimate controller with integrated term resitor -20 meters- 2 Persystec lambda controllers -20 meters- Lawicel CANUSB interface with term. resistor. Total resistance is ok, I measure about 60 ohms.

 

At 1Mbits/s, the Ultimate controller receive and displays the messages I send from the PC, 40 meters away.

But it didn't displays the messages comming from the Persystec controllers, 20 m. away. These messages are seen by the PC, also 20 m. away.

 

At 500kBits/s, everything is ok, everyone receive all messages.

 

On the oscilloscope, signals seem perfect, with good rising and falling edges. Recessive voltage is 2.5V.

I should check the exact active levels.

 

Any idea ???

 

Angelo

 
Posted : 19/04/2023 10:56 am
(@admin)
Posts: 1460
Member Admin
 

Hi,

I would first try with a shorter cable. Maybe there could be a ground potential difference between the units too? You can try to pull a ground cable between the units. The CAN bus tolerates quite large ground potential differences, so I don't really think that is the problem, but you can check. 

Also make sure to run latest software and firmware. There have been some CAN bus improvements lately. 

 
Posted : 20/04/2023 11:30 pm
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