The 14507549 RS-232 to RS-485 Adapter Module (“Adapter”) allows a notebook or desktop PC to communicate with controllers on a C-Bus in an Excel Building Supervisor (XBS) system (Ver. 1.2.2 or later). The Adapter is external to the PC and interfaces to the PC COM port via a RS-232 signal cable. A special WYE power cable routes power to the Adapter from the PC keyboard connection. The Adapter is able to drive a full-length C-Bus via a standard XW570 C-Bus cable. The Adapter provides complete opto-isolation to eliminate ground-loop problems. It also provides built-in resistors that are externally selectable for proper C-Bus biasing and termination. Built-in LEDs indicate C-Bus activity. The Adapter can be used in European applications that require CE certification.