3-20 C30 Controller System GE Multilin3.2 WIRING 3 HARDWARE3The baud rate for this port is fixed at 19200 bps.Figure 3–21: RS232 FACEPLATE PORT CONNECTION3.2.8 CPU COMMUNICATION PORTSa) OPTIONSIn addition to the faceplate RS232 port, the C30 provides a rear RS485 communication port.The CPU modules do not require a surge ground connection.Figure 3–22: CPU MODULE COMMUNICATIONS WIRINGb) RS485 PORTSRS485 data transmission and reception are accomplished over a single twisted pair with transmit and receive data alternat-ing over the same two wires. Through the use of the port, continuous monitoring and control from a remote computer,SCADA system, or PLC is possible.To minimize errors from noise, the use of shielded twisted pair wire is recommended. Correct polarity must also beobserved. For instance, the relays must be connected with all RS485 “+” terminals connected together, and all RS485 “–”terminals connected together. Though data is transmitted over a two-wire twisted pair, all RS485 devices require a sharedreference, or common voltage. This common voltage is implied to be a power supply common. Some systems allow theshield (drain wire) to be used as common wire and to connect directly to the C30 COM terminal (#3); others function cor-rectly only if the common wire is connected to the C30 COM terminal, but insulated from the shield.NOTENOTE
