Generally about the RS232 to RS485 converter / RS232 to RS422 converter:
The serial RS232 to RS485 converter and RS232 to RS422 converter units, also called serial converters, are small electronic devices used to convert a serial RS232 signal, (for example the COM port in older computers) into either RS485 or RS422 signals. The typical serial converter does this in both directions which is also referred to as a bi-directional converter.
Some of these converters can convert from RS232 to both RS485 and RS422 however many standard models only has one of the protocols.
Why use a RS232 - RS485 /RS422 converter? Most newer consumer electronics comes with an USB, Firewire or other high-speed communication port, however a lot of industrial and commercial equipment, both old and new, is made only with a RS485 or RS422 serial communications port. So in order to transfer data from a RS232 serial interface engineers need a converter to be able to connect to a RS485 or RS422 interface. The reason is that the serial RS232 protocol is, even its old, a very reliable, stable and solid communication protocol, which can easily be implemented with existing industrial equipment.
So what is a RS232 to RS485 converter?
RS485, also known as TIA/EIA-485 is a standard serial communications protocol defining the electrical characteristics of a serial converter, drivers and receivers for use in balanced RS485 digital multipoint systems. Even RS485 is not commonly as popular as RS232 it is extremely useful for converters in industrial and commercial environments. A RS232 - RS485 converter is often used in industrial data acquisition and control applications where multiple serial devices communicate with each other through a converter.
The advantage of the RS485 protocol is that this it can transfer data over longer distances, up to 4000 feet, and have up to 32 nodes per single network, and it can be used for multi-point networks where multiple serial devices are setup in a bus network.
The RS485 converter interface uses two wires for communication, one for transmitting and one for receiving data, which is referred to as a half-duplex communication converter. The typical common-mode voltage range for a RS485 converter is -7V to +12V.
Usually a RS232 - RS485 converter is the preferred way to establish multi-point networks when working with RS232 devices. This is a method for connecting multiple RS485 devices with each other over a two-wire network. However since only a true RS485 network can have addressable serial RS485 devices, the RS232 converter needs to be addressable either by software or by DIP switches when using it in this type of configuration.
And what is a RS232 to RS422 converter?
A RS232 - RS422 converter is a 4-wire, full-duplex, differential protocol with multi-drop capabilities and a recommended distance limit of 4000ft. ANSI/TIA/EIA-422-B is the American national standard for the RS422 protocol.
The RS422 converter is used for data transmission, using balanced or differential signaling, it is mainly used in industrial and commercial environments since lots of process equipment and machinery have this protocol built-in. The RS232 - RS422 converter is also often used in older serial devices such as older PLC's and terminal equipment.
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 a RS232 to RS422 serial converter might be in point-to-point communications, such as extending an existing RS232 line. Extending a RS232 line is done by converting the RS232 signal into RS422 and then back to RS232 at the remote end. This way you can extend the RS422 signal for up to 4000 feet.
There are several factors to consider when choosing a RS232 - RS422 converter. For example you need to consider the noise level in the environment surrounding the serial converter. If there is a lot of environmental electrical noise then an optical isolated converter is preferred. We also highly recommend using paired twisted cable for connecting most converters.