RS-485 supports inexpensive local networks and multidrop communications links, using the same differential balanced line over twisted pair as RS-422. It is generally accepted that RS-485 can be used with data rates up to 10 Mbit/s and distances up to 1,200 m (4,000 ft), but not at the same time. A rule of thumb is that the speed in bit/s multiplied by the length in metres should not exceed 10. Thus a 50 meter cable should not signal faster than 2 Mbit/s. Under some conditions it can be used up to data transmission speeds of 64 Mbit/s.

RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. This allows RS-485 to implement linear bus topologies using only two wires. The recommended arrangement of the wires is as a connected series of point-to-point (multidropped) nodes, i.e. a line or bus, not a star, ring, or multiply connected network. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. If a star configuration is unavoidable, special RS-485 star/hub repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans.