What is RS232 and What is it Used for?

Summary

RS-232 is a serial communication standard for transmitting data between devices. It was once widely used in industry and remains common in some legacy equipment.

A common connector is the 9-pin DB9. RS-232 encodes binary data using voltage polarity: positive voltage represents 0, and negative voltage represents 1.

RS-232 can connect PLCs to compatible equipment, including HMIs, computers, motor drives, robots, vision systems, and I/O modules. The video distinguishes between:

• DTE (data terminal equipment), such as a computer
• DCE (data communications equipment), such as a modem

Two devices of the same type may need a reverse null modem cable to communicate. The video notes that PLCs are typically DTE, while connected devices are typically DCE. A familiar example of RS-232 communication is a computer sending commands to a printer.

Limitations and current use

RS-232 has relatively low data speeds—around 20 kilobytes per second—and a typical maximum cable length of about 50 feet. Beyond that distance, cable resistance and voltage issues can become problematic.

USB and Ethernet have replaced RS-232 in many applications, but adapters can connect older RS-232 equipment to newer standards. Because of its long history and low cost, RS-232 is still found in industrial equipment.

Guide or tutorial points

The video introduces RS-232, covering its signal encoding, device roles and cabling, common applications, and limitations.

Main speaker or source

• RealPars narrator — introductory industrial-automation explainer.