| Originally, large voltage swings were used in RS-232 to increase the signal-to-noise ratio when transmitting data over long distances. |
| RS-485 uses only two wires for bi-directional communication, althoug not both directions at the same time. They are differential signals which are more immune to common-mode noise picked up on the pair of signal conductors. The two conductors used inn RS-485 act like a true transmission line and reflections are ellimiated by terminating the bus at each end. Also, multiple devices connected to an RS-485 network can act as the master to initiate data transfer. |
| RS-422 uses separate pairs of signals for transmitting and receiving data. Thus, data can be transferred in both directions simultaneously. |