Have
you ever had a device communicate fine on the test bench, but bring down the whole
RS-485 multi-drop line in the field? The key to solving such a pesky problem is
to understand that any RS-485 device trying to transmit views the rest of the
RS-485 network as a collection of resistances in parallel. While the transmitter
expends energy to try to create a voltage difference on the line, the collection
of resistances act togather to reduce this difference toward 0v. This application
note discusses this possible cause and a test method for troubleshooting.
