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 devices used to convert a serial RS232 signal, (for example the COM port in older computers) to either RS485 or RS422 signals. The typical converter does this in both directions meaning from RS232 to RS485 / RS232 to RS422 but also from RS485 / RS422 to RS232, this is also referred to as a bi-directional converter.
Many of these converter units can convert from RS232 to both RS485 and RS422 but some only has either a RS485 or a RS422 converter feature.
Why use a RS232 to RS485 converter / RS232 to 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, comes with a RS232 to RS485 converter or RS232 to RS422 converter communications port. So in order to transfer data from a RS232 to RS485 converter or RS232 to RS422 device to for example a computer, engineers need a RS232 to RS485 converter or RS232 to RS422 converter. The reason is that the serial RS232 to RS485 / RS232 to RS485 converter 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 converter protocol defining the electrical characteristics of converter, drivers and receivers for use in balanced RS232 to RS485 digital multipoint systems. Even RS232 is not commonly as popular as RS422 it is extremely useful for converter units in industrial and commercial environments. A RS232 to RS485 converter is an often used interface in data acquisition and control applications where multiple nodes communicate with each other through a converter.
The advantage of a RS232 to RS485 converter is that RS485 can transfer data over longer distances, up to 4000 feet, and have up to 32 nodes per single network, and a RS232 to RS485 converter can also be used for multi-point networks.
The RS485 converter interfece uses two wires for communication, one for transmitting and one for receiving data, which is referred to as a half-duplex communication converter. The common-mode voltage range for a RS485 converter is -7V to +12V.
Usually a RS232 to RS485 converter is the preferred way to establish multi-point networks. This is a method to connect multiple RS232 to RS485 devices with each other over a RS232 to RS485 converter two-wire network. This is because a RS232 to RS485 converter can easily be addressed either by software or by DIN-switched on the particular unit.
And what is a RS232 to RS422 converter?
A RS232 to RS422 converter is a 4-wire, full-duplex, differential protocol with multi-drop capabilities and a recommended distance limit of 3600ft. ANSI/TIA/EIA-422-B is the American national standard for a RS422 converter. The RS422 converter is for data transmission, using balanced or differential RS232 to RS422 converter signaling, with non-reversible, point to point or multi-drop, and is terminated only on the end of the line opposite the RS232 to RS422 converter / RS232 to RS485 converter. In contrast to RS232 to RS422 converter EIA-485 (which is multi-point instead of multi-drop), EIA-422/V.11 does not allow multiple RS232 to RS422 converter drivers but only multiple receivers. Due to loading limitations one of the best uses of a RS232 to RS422 converter might be in point-to-point communications, such as RS232 to RS422 converter extension cords.
The RS232 to RS422 converter is however also very effective as a line extender, for example to extend a RS232 to RS422 converter wire. You do this by converting the RS232 signal to RS422 and then back to RS422. This way you can extend the RS422 signal up to 3600 feet.
The RS232 to RS422 converter is also often used in older RS232 to RS422 converter devices such as older PLC's and terminal equipment.
There are several factors to consider when choosing a RS232 to RS422 converter. For example if you are using a RS232 to RS422 converter you need to consider the noise level in the environment surrounding the RS232 to RS422 converter. A typical RS232 to RS422 converter is fairly resistant to noise however the wire connecting to the RS232 to RS485 converter or RS232 to RS422 converter needs to be protected against noise.