How do I properly terminate my RT CAN equipment?
In order to ensure that reflection does not cause communication failure, the transmission line must be terminated. This cannot be done in the RT hardware itself, as it depends on the installation as to whether it is required or not. If this is not done correctly, then it is likely that CAN interface will not work, or will have erratic behaviour.
Both ends of the pair of signal wires (CAN_H and CAN_L) must be terminated. This is because communication flows both ways on the CAN bus. CAN_L is pin 2, and CAN_H is pin 7 on the standard 9-Pin D-Sub connector. The termination resistors on a cable should match the nominal impedance of the cable. ISO 11898 requires a cable with a nominal impedance of 120 ohms, and therefore 120 ohm resistors should be used for termination. If multiple devices are placed along the cable, only the devices on the ends of the cable need termination resistors. The diagram below gives an example of how to terminate a high-speed network.