What do the terms “half duplex” and “full duplex” mean with regard to RS-485 products?
Half duplex means that data in a network can be transmitted in only one direction at a time. Half duplex RS-485 transmission requires only one twisted pair cable, so the driver output and corresponding receiver input are connected together on the IC (i.e., the IC is either transmitting or receiving at any given time). A full duplex network allows data transmission in both directions at the same time, so two twisted pairs are required, and the transceiver needs to be able to transmit and receive at the same time. This requires that the driver outputs be separate from the receiver inputs. Full duplex operation can improve system performance by increasing throughput. For example, in a master/slave full duplex system, the master can be polling the next slave for data, while it is receiving data from the previously polled slave.
