Fig. 6.-1 Pin usage table for the 9-pin D-type connector (X1) The RS-485 interface of the RER 133 module is shown in Fig. 6.-2. The connector (X2) is an 8-pin Weidm¸ller terminal block. If GND (pin 5) is used, then it is required for all other nodes to be isolated as well.
The EIA RS-485 Specification labels the data wires "A" and "B", but many manufacturers label their wires "+" and "-". In our experience, the "+" wire should be connected to the "A" line, and the "-" wire to the "B" line. When wiring RS-485 , use a shielded twisted pair cable with an internal impedance of 100-120Ω. Examples of recommended cables are CAT 5, Belden RS-485 (9841- 9844) and Alpha Wire (Alpha 6222-6230)
The shield of the cables must be directly connected to ground in one of the nodes. In the other nodes the connection should be made via a capacitor, i.e. if the shield of the cable is connected to pin 1 in node 1, all the other nodes must be grounded using pin 2.