Connectiing ABB REF542 to Stallion EasyConnection using RS-485

The project in which I am involved requires to connect ABB REF542 relay units to Stallion EasyConnection module which is connected to Honeywell PlantScape Servers. I am experiencing problem in establishing communication between the server and ABB REF542. The serial communication is of 2 wire RS-485. A resistor of 120Ohms is used in one end. There is no reply from ABB REF542 for the server requests. Communication port of ABB was checked and found to be working.

The cable used is a twisted pair cable and no grounding is used in Stallion EasyConnection side. Also the Stallion EasyConnection is a asynchronous type. Can any one help me in troubleshooting this problem?