I am testing my CANopen boards with 20m long cable communication@1M, I used below setup and the two cards could communicate for about 7~8 seconds, then stop. when I use 5m cable@1M. the communciation was ok.
From the bus waveform we captured, It seems that the RX card can’t send the ACK signal to TX card, I attached the waveform.
The interesting thing I found is that the communication was ok when there was 120 Ohm resistor at one end of the bus( either end), but failed with both the resistors. When using short cable, the communication was ok with both the resistors.
Could you please suggest what may cause such kind of problem?
Thanks in advance!