What is the difference between a “2-wire” and a “4 wire” RS-485 network?
A “2-wire” system uses a single twisted pair of wires (don’t forget to allow for a GND wire) for the RS-485 bus. This reduces cable costs, but limits the network to half duplex communications. Parts denoted as “half duplex” would be used in a 2-wire system. A “4-wire” system requires two twisted pairs (plus GND), making the cabling more expensive, and bulkier. The 4-wire system allows full duplex transmission, meaning that a particular device can both send and receive data at the same time, thereby improving throughput. Use parts marketed as “full duplex” for 4-wire systems.
