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What is RS232
The RS-232 interface (TIA / EIA-232) is related to the serial data transmission interface standard between the transmitter or terminal (Data Terminal Equipment, DTE) and the receiver or communication equipment (Data Communications Equipment, DCE), was established by the Electronic Industries Alliance (EIA) in 1960.



RS232 is widely used in the connection of peripherals of the computer’s serial interface. Connect the cable to mechanical, electrical, signal, and transfer processes, such as Servo Controllers, CNC Machines tools and PLC machines. but most computers currently do not have RS232 COM ports, because USB to Serial Converter is more convenient to connect devices such as serial printers, scanners and GPS devices.



Since the communication data is based on the voltage on the wires relative to the ground level, the ground connection must be made between the RS-232 communication device. the following is RS232 wiring diagram and Specification Summary.


What is RS422
RS-422, also known as TIA/EIA-422, is a technical standard that specifies electrical characteristics of a digital signaling circuit originated by the Electronic Industries Alliance.



The RS-422 line is 4 wires for data transmission and one common GND ground wire, allows you to send and receive data on separate lines (full duplex) simultaneously, each signal uses two wires to pass the data. The differential voltage on the A and B wires represent the digital value. If B>A, the value is 1. If A>B, the value is 0.



It has a maximum transmission distance of 4000 feet (about 1219 meters) and a maximum transmission rate of 10 Mb/s.



Contrast to RS232, RS422 adopts a combination of balanced driver and a differential receiver, which has strong anti-common mode interference capability enables systems to operate over long distance, much better than RS232.


What is RS485
The most widely used serial interface is the RS485 or EIA-485 protocol. the RS-485 standard specifies differential signaling on two lines to generate effective common-mode noise cancellation. It has a great advantage over RS232 interfaces by using a multi-point topology, multiple receivers and transmitters can be connected.



RS485 can operate in half-duplex mode (with 2 contacts) or full-duplex (with 4 contacts), the transmission distance can reach up to 4000 feet (about 1219 meters) and the maximum transmission rate is 10 Mb/s. but if the distance is too long, you should put an Industrial RS-485 repeater/Isolator in the middle or at the beginning of the bus, the repeater with photoelectric Isolation can be extended to 3000 meters.



RS485 is used commonly as a protocol for POS, metering instruments, data acquisition and control and especially in noisy environments, which make data transmission on a higher speed and longer distance, the RS485 is also common use for computers, PLCs, microcontrollers and intelligent sensors in scientific and technical applications.


More Info:https://www.upcomnet.com/blog/difference-between-rs232-rs422-rs485-converters-2.html