What is the termination resistor purpose and how to install it in the BM communication network?

The termination has the main goal to reduce the reflections that the signal may suffer at the line end. The signal reflections produce noises in the network, which can create communication issues. When the termination is well-defined, the signal energy is completely absorbed and does not exist in signal reflection.

As an example, see the image below. Notice the difference between the signals observed by an oscilloscope attached to a communication network with a 54 Ω termination resistor (on the left side) and with a 120 Ω termination resistor (on the right side).

The 120 Ω resistors always have to be installed at the communication network end, not depending on their length. In this case, must be installed at the BM-HMI and BM-MM terminals.