One should wonder why the use of RS-232 is any different than the use of an RS-422 and what the difference between each one of them is. Both of these are telecommunications standards and there are some differences between them and we are going to get into that in this article.
RS-232 is the most commonly used serial interface even though it was one of the first ones to exist, the creators really did a great job with it. It is used as the standard component on most computers that use Windows and in fact, most of the PC purchases done will immediately be including one within. Sometimes, as it happens, there is even more than one RS-232 port (that’s how popular they are).
Most of this popularity comes due to convenience. RS-232 is so readily available that people start using it as the standard unit, without really going into other resources. Most PC purchases include one and as such, that is that. There are, however, some disadvantages to it.
The first one is limited distance. The cable lengths have a limit of 50 ft. and sometimes even less, this is definitely not positive. Some manufacturers might claim to have a little more length, but that isn’t recommended as it is not a part of what is specified for an RS-232. Another disadvantage is that the RS-232 is susceptible to noise. It is single ended and this means that both the transmit and receive lines are on common ground. Finally, only one RS-232 device can be connected per port. This isn’t very good, since in the case that you have 2 meters to connect to a PC, you’ll need 3 ports.
The RS-422 on the other hand, although similar to the RS-232 can be programmed the same way, it may also offer other advantages, as well as have its own disadvantages. The first problem anyone finds in it is that you either need an RS-422 port or an RS-422 to 232 converter, since most PC’s are ready for RS-232.
The advantages, however, include long distances runs. Up to 500 feet is usually doable, and in some cases further distances are possible. The RS-422 is also noise resistant, since it uses separate transmit and receive pairs providing it better noise immunity as well, with a total of four wires in the midst of it.
The best part is that usually 32 devices can be used per port, and with repeaters it goes even further than that. Each device is designed a unique address that distinguishes it from the others, facilitating the process to great lengths. The addresses that each device has can be defined either by software or by switches, depending on the design of the device itself.