Published July 1999

THE ART AND SCIENCE OF RS-485

by Bob Perrin

Start • Arm Yourself • RS-485 101 • Getting Grounded • Shielding • Topology • Termination • Idle-state Biasing • Transients • Review Time • Sources

REVIEW TIME

RS-485 is not difficult, but any workhorse requires care and feeding. Before starting your RS-485 project, arm yourself with the TIA/EIA-485-A and TSB-89 documents.

While designing, rely on the many examples others have published in articles and application notes. Keep an eye out for non-network-related problems like ESD, power-supply noise, and ground bounce. The currents switched at the drivers can be quite high. Also watch out for new parts like the MAX3095. They may be just what the doctor ordered for your future designs.

Engineering is simply keeping track of details and making tradeoffs. RS-485 is no different. We’re lucky because most of the really ugly tradeoffs have been made by the standards. But you probably don’t have to worry about having your job phased out as there are still plenty of other details left to keep track of.

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