RS-232 stands for Recommend Standard number 232 and C is the latest revision of the standard, also referred to as EIA232. It is a telecommunications standard used for binary serial communications between devices, the devices are usually referred to as a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). Since the transmit data and receive data are separate circuits it can operate with a full-duplex protocol meaning that it can send and receive data at the same time.
In general, many modern applications for RS232 use only the electrical standard (3-wires, TDX, RXD and Common), however some devices makes use of handshake signals but are often left out or disabled.
The cable length limit for RS232 is 50 feet and the valid signals for RS232 are plus or minus 3 to 15 volts, however signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the power supplies available within a device. Usually a D-subminiature (DB9) connector is used for connecting RS232.

EIA-485, also known as TIA/EIA-485 or RS-485 is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. Even RS485 is not commonly as popular as RS232 it is extremely useful in industrial and commercial environments. RS485 is a often used interface in data acquisition and control applications where multiple nodes communicate with each other.
The advantage of RS485 over RS232 is that RS485 can transfer data over longer distances, up to 4000 feet, and have up to 32 nodes per single network, whereas R232 cannot be used for multi-point networks.
RS485 uses two wires for communication, one for transmitting and one for receiving data, which is referred to as half-duplex communication. The common-mode voltage range for RS485 is -7V to +12V.

4-wire, full-duplex, differential with multi-drop capabilities and a recommended distance limit of 3600ft. ANSI/TIA/EIA-422-B is the American national standard for RS422. RS422 provides for data transmission, using balanced or differential signaling, with unidirectional/non-reversible, point to point or multi-drop, and is terminated only on the end of the line opposite the transmitter. In contrast to EIA-485 (which is multi-point instead of multi-drop), EIA-422/V.11 does not allow multiple drivers but only multiple receivers. Due to loading limitations one of the best uses of RS422 might be in point-to-point communications, such as RS232 extension cords.

A universal asynchronous receiver/transmitter (abbreviated UART), is the key component of the serial communications subsystem. An UART controller takes bytes of data and transmits the individual bits in a sequential fashion and at the destination, a second UART re-assembles the bits into complete bytes. The common physical apperance of the UART is a plastic molded micro chip such as FTDI or MAX232. Most modern UART’s are version 16550 and more recently 16650.

Since most newer computers does not come with a serial RS232 COM port the use of USB to serial RS232 adapters and converters has become popular. A USB to serial adapter can be either a USB to RS232, USB to RS485 or USB to RS422 adapter, wither way is simply converts RS232, RS485 or RS422 serial data to USB data signals. It’s a very easy, useful and effective way to connect any serial device to a computer. There are however some limitations and common challenges by using a USB to serial adapter, click here for more information. USB to serial adapters are used both in industrial, commercial and private environments.

With a serial Ethernet server, also called a Serial Device server or Serial over Ethernet converter, you can connect any serial device remotely to a computer over a LAN or Ethernet network. It simply converts all serial data to packets which can be sent over a CAT5 cable. It does this bi-directional which means that it can communicate both ways, serial to Ethernet and Ethernet to serial. A Serial Device Server is mostly used in commercial and industrial environments.