RS-485 (officially TIA/EIA-485) is a standard for serial communication widely adopted in industrial automation. Designed to overcome the limitations of RS-232C, RS-485 utilizes differential signaling over a twisted-pair cable. Unlike the single-ended signaling of RS-232C, this balanced transmission method provides high immunity to common-mode noise, ensuring stable performance even in electrically noisy environments.
Key advantages of RS-485 include long-distance communication capabilities--up to 1.2 kilometers (4000 feet)--and support for multi-drop networking. While RS-232C is limited to one-to-one connections, a single RS-485 bus can connect a master controller (such as a PC or PLC) to multiple slave devices, including programmable power supplies, sensors, and drives. Due to its robustness and wiring simplicity, RS-485 serves as the physical layer for many industrial protocols, such as Modbus RTU and PROFIBUS.