AiVibeRS-485 (TIA/EIA-485)
RS-485, formally TIA/EIA-485, is an electrical standard for differential serial communication that supports multiple devices on a shared twisted-pair bus over long distances, and is the physical layer for Modbus RTU, PROFIBUS DP and many other industrial protocols.
RS-485 transmits each bit as the voltage difference between two wires, commonly labelled A and B, which gives strong immunity to common-mode electrical noise. It defines electrical characteristics only, not a protocol, and supports multipoint networks in which a device enables its driver only while transmitting. Most installations use two-wire half-duplex operation, in which devices take turns on the same pair, though four-wire full-duplex arrangements also exist.
Its robustness, low cost and support for long cable runs and many nodes made RS-485 the usual physical layer for industrial serial networks. Modbus RTU, PROFIBUS DP, BACnet MS/TP and many proprietary drive, meter and instrument protocols run over it. It remains common for connecting energy meters, VFDs, temperature controllers and legacy equipment to PLCs and gateways.
Reliable RS-485 networks need a daisy-chain topology rather than a star, termination resistors at both ends of the bus, biasing to hold the line in a defined idle state, twisted-pair cable and attention to grounding and shield connection. The standard expresses the load each receiver places on the bus in unit loads, which limits how many devices can share a segment without repeaters. Data rate and maximum cable length trade against each other.
Key points
- Differential signalling over twisted pair resists electrical noise
- Defines electrical characteristics, not a communication protocol
- Physical layer for Modbus RTU, PROFIBUS DP and BACnet MS/TP
- Needs daisy-chain topology, termination and biasing
- Higher data rates reduce the maximum usable cable length
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory, whose edge devices and AI agents let people talk to PLC, CNC and robot controllers in plain language. Agents only propose changes, a trained operator confirms each one, and the AI Factory never replaces a machine's control or safety systems.