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Grant Baker

CAN Lambda / Resistor

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Hi Guys,

Have searched for this, but not come up with a definitive answer...

When installing a CAN Lambda on a wire-in or plug-in ECU, do you need a terminating resistor?

It doesn't say in the instructions, but in the help files, it does indicate that it would be needed...

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All our ecus have one built in so nothing needed at ecu end, but the Link CAN lambda doesn’t (to allow multiple lambdas on same bus).  So you should add a 120ohm resistor near the far end of the bus.

Having said that if your bus is less than about 2 meters long then it will usually work fine without the termination at the far end - always best to do it right first time though.

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Resistor added.

Interesting while setting this up and following the manual for CAN setup, had an issue.

In the CAN Devices tab, I selected the CAN Lambda, then tried to update the speed to 1mb/s (from 500mb/s). Then proceeded to "send". It said it failed and to cycle power, which I did by unplugging the connector and reconnecting.

Tried it several times but it didn't succeed, so had to alter the main bit rate on the CAN Connection to 500mb/s.

Anybody else had this?

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Its easy to get bit errors if the CAN bus does not have a 60 ohm load, the resistor although should be applied to each end of the bus they can practically be placed inbound somewhat, the resistance provides a load so the electronic bus driver that helps it drive the voltage up and down fast without skew (the angle of the rise and fall of the pulse)

The faster you run the bus say 1Mbps then the skew becomes more important to control also at that speed on a transmission buss you can easily have on transmission spanning 6 Meters, and thats where the end of line resistors help and it damps out the reflected data, returns it to ground if you like.

Just make sure the can bus has a termination resistor on both ends or as near as practicle.

The other thing is the wires much be twisted this give the transmission line an impedance and stops a lot of mainly magnetic interference. 

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Thanks. 

Resistor is looped around to join the ends of the trunk 30mm past the CAN LAMBDA. 

Also getting lots of CAN errors. 

Will check the twisting tomorrow morning but that is correct iirc. 

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19 hours ago, Grant Baker said:

Also getting lots of CAN errors. 

What errors are you getting Grant, the CAN Bus is quite informative but can generate spurious errors when one thing is wrong.

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