Serial interfaces are used in most electronic equipment, some of the original serial interfaces include RS-232, RS-422and RS-485. Serial interfaces provide a single path for data transmission wirelessly or over a cable. With the prevalence of high-speed data, a serial interface is the most viable option for communications over larger distance. Serial interfaces are used to provide standardized logic levels from transmitters to receivers, define the transmission medium and connectors, and specify timing and data rates. They can perform serial-to-parallel and parallel-to-serial conversion or specify a basic data protocol, in some cases.
RS-232 is one of the oldest serial interfaces and is established as a method of connecting data terminal equipment (DTE) like electromechanical teletypewriters to data communications equipment (DCE). Serial interfaces can also be used for connections to video terminals, computers, and modems. it is still widely used in embedded computer development systems, scientific instruments, and all sorts of industrial control equipment.
RS-422 or TIA/EIA-422, is a technical standard defined by the Electronic Industries Alliance. It specifies the electrical characteristics of a digital signaling circuit. As high as 10 Mbit/s data transmit rate can be achieved through differential signaling , or may be sent on cables as long as 1500 meters. Some of the systems directly interconnect using RS-422 signals, or RS-422 converters may be used to extend the range of RS-232 connections. RS-422 standard only defines signal levels; few other properties of a serial interface like electrical connectors and pin wiring, are set by other standards.
RS-485 the interface defined by the EIA/TIA standard, is now called TIA-485. It defines not only a single device-to-device interface but also a communications bus that can be used to form simple networks of multiple devices. Its configuration and specifications extend the range and data rate beyond the RS-232 interface capabilities. The RS-485 is for higher speeds over longer ranges or if duplex networking capability is required.