To the left of the I/O connections on the , there are three DIP switches for terminating and biasing the RS485 communication bus.

The correct configuration depends on the topology of the RS485 bus. In most cases, activating all resistors is the recommended choice. Do this if you are unsure. This is different if the is not at the end of the communication bus or if another device has active bias resistors.

If your is manufactured before 1 August 2024:

(These devices have white switches coming from a black component).

The termination resistor is active when the corresponding DIP switch is in the down position.
The bias resistors are active when the corresponding DIP switches are in the down position.

If your is manufactured after 1 August 2024:

(These devices have white switches coming from a red component).

The termination resistor is active when the corresponding DIP switch is in the up position.
The bias resistors are active when the corresponding DIP switches are in the up position.

Eastron SDM120M