How many resistor on CAN Bus?

Your wiring isn't the impedance you think it is, or you don't have resistors at each end of the line???

I know nothing about the CAN bus, but 120 ohms seems a highly peculiar line termination value. 70, or 100 ohms is more likely. Check it. Do you have both ends of the bus terminated?

There are three distinct issues.

1. CAN must be terminated at each end of the main bus.

1. There is a maximum stub length to each device.

2. The controller does not sit at the 'end' of the bus in a multidrop system.

Violate any of the above and your CAN bus may not operate as advertised. The max speed depends on the length of the system.

Cheers

PeteS

That's the usual termination value. The original description appears to be of a bus with only a single terminator.

It's also worth noting that there is no master on a CAN bus.

Robert

There should be a resistor at BOTH ends of the bus.

Meindert

This morning I insert a resistor at the other side of the bus, near the master, and it works! Thank you!

That's nastily close to the absolute maximum of 250m at that bit rate. It's right on the rule-of-thumb limit of 50e6 (m*bit)/s. You will have to be quite careful about cabling, transceivers and oscillator tolerances to make that work reliably.

There is no such thing as "the" master on a CAN bus. CAN is a multi-master bus.

Bad. Stretching the bus length this close to the limit, you absolutely need terminators at both ends.

In the original post Giulia mentioned that she is using CANopen on top of CAN, CANopen has an master. It is called Network Management (NMT) master. It's only a a logical behavior, of course no influence of the physical and Data Link Layer protocol as such.

Heinz

Ah, Missed that.

Robert