The serial port on the TriStar is opto-isolated per UL requirements. For this reason, the TriStar serial port is “port powered”, which means it requires a small amount of power from the host (PC or other device). In addition to pins 2,3,& 5, pin 4 and/or 7 should be connected. For more information, refer to the document, “TriStar RS-232 Wiring”.
Tristar RS232 Wiring