I have a piece of equipment that uses RS485 with RJ45 jacks and I was wondering if I needed special cabling with only 4 of the wires phyically connected in the jack or could I just use regular CAT5 Ethernet cabling with all eight wires present? The specs that I have for the cable only list
4 wires, but they are in the same order and place as a regular CAT5 Ethernet cable. The cable will go between two like devices over RS485 connected by RJ45 jacks.
RS-485 requires only a single twisted pair assuming that proper "fail safe" termination is used (if no termination is used, you also need a signal ground reference).
If standard CAT5 Ethernet cabling is used, make sure that you use the wires from the _same_ twisted pair for RS-3485 A and B connections. Using the A signal from one twisted pair and the B wire from an other twisted pair is going to ruin the noise immunity quite quickly :-).
Paul
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