RS-232, RS-422 and RS-485 are serial connections which can be found in various consumer electronics devices. Namely, RS-232 (ANSI/EIA-232 Standard) is the serial connection which can be historically found on IBM-compatible PCs. It is employed in many different scenarios and for many purposes, such as connecting a mouse, a printer, or a modem, as well as connecting different industrial instrumentation. Due to improvements in line drivers and cables, applications often expand the performance of RS-232 beyond the distance and speed limits which are listed in the standard. RS-232 is restricted to point-to-point connections between PC serial ports and various other devices. RS-232 hardware can be employed for serial communication up to distances of 50 feet.
On the other hand, RS-422 (EIA RS-422-A Standard) is the serial connection which can be historically found on Apple Macintosh computers. RS-422 employs a differential electrical signal, as opposed to unbalanced signals referenced to ground with the RS-232. Differential transmission employs two lines each for transmitting and receiving signals which lead to greater immunity to noise and the signal can travel longer distances as compared to the RS-232. These advantages make RS-422 a better option to consider for industrial applications.
Finally, RS-485 (EIA-485 Standard) is an improvement over RS-422, because it increases the number of devices from 10 to 32 and defines the electrical features necessary to safeguard adequate signal voltages under maximum capacity. With this enhanced multi-drop capability, one is able to create networks of devices connected to a single RS-485 serial port. The noise immunity and multi-drop capability make RS-485 the serial connection of choice in industrial applications requiring many distributed devices networked to a PC or other controller for data collection, HMI, or other operations. RS-485 is a superset of RS-422; therefore, all RS-422 devices can be controlled by RS-485. RS-485 hardware can be employed for serial communication with up to 4000 feet of cable network.