Figure 2. Typical Isolated RS-485 Circuit Using Digital Isolators
This implementation shows the connections between the transceiver and the digital isolators.
Note that the driver enable (DE) and receiver enable (/RE) are connected to form a single
direction control. In other implementations, these two signals may be separately controlled, to
put the transceiver in a low-power state, for example. This requires one additional digital isolator.
Note that although the electronics at the various nodes are galvanically isolated from each other
by the digital isolators, a ground wire connects the transceivers on all the nodes. This grounding
scheme is needed to keep the transceivers referenced to a common voltage potential and is
necessary for isolated and non-isolated networks.
Another implementation of the isolated interface is shown in Figure 3. In this Illustration,
optocouplers are used to transmit the digital signals across the isolation barrier. Optocouplers
are commonly used in applications where the superior performance of digital isolators is not
needed.