Q: I cannot communicate with my RS485 or RS422 devices. What is the problem?     A: First verify that the port is configured for 485 or 422 mode. For all products except the RCS/4000 you can check this with the browser interface - Port Status page. When switching from RS-232, a port server reboot is required. Furthermore, the port needs to be opened before the browser will indicate the proper interface. Assuming that it is correctly configured, the most common RS-485 problem is termination. If the receive lines end at the RCS, then the lines must be terminated with a 100-120 ohm resistor between the A and B receive lines at, or as close as possible to, the connector. On the RCS/4000 you must check the jumper settings on the board to see how the port is configured. Also, on the RCS/4000, the terminator is already built into the board. Additionally, for devices that use + and - labeling, we assume B to be + and A to be -.     Answer Last Updated: June 5, 2008