Hints on RS-485 networks: Termination resistors You always need them. Termination resistors should be added to the nodes located at the ends of the line. The communication may works without them if the wire is short enough and/or the bit rate is low. Pull up/down resistors a.k.a failsafe bias resistors Why you need it is well explained here: https://electronics.stackexchange.com/a/284788/88486 When you need it: It depends on the RS485 transceiver IC. Most modern transceivers include these. Common ground Do you have a common ground between your transceivers? RS-485 is not a 2 wire network. Besides the A-B lines it requires ground. See: http://store.chipkin.com/articles/rs485-rs485-cables-why-you-need-3-wires-for-2-two-wire-rs485 Schematics at http://www.analog.com/media/en/technical-documentation/application-notes/AN-960.pdf page 4. Isolation When you deal with long links, you have to take care of isolation. Page 8 at http://www.analog.com/media/en/technical-documentation/application-notes/AN-960.pdf