RS-485 (formally TIA/EIA-485) is the physical-layer serial standard that underpins a huge amount of industrial communication. It is not a protocol itself but a specification for the electrical signalling that carries protocols like Modbus RTU, PROFIBUS DP, and BACnet MS/TP over long distances on inexpensive twisted-pair wiring.
RS-485 / Serial in one line: RS-485 is a serial communication standard that uses balanced differential signalling over a twisted pair to support multidrop networks of up to 32 or more devices at distances up to about 1,200 metres, providing the robust physical layer for protocols such as Modbus RTU and PROFIBUS.
RS-485's durability comes from differential (balanced) signalling. Data is sent as the voltage difference between two wires (A and B) rather than relative to ground. Because electrical noise picked up along a cable run affects both wires almost equally, the receiver rejects the common-mode noise and reads only the difference - which is why RS-485 works reliably over long runs in electrically noisy plant environments where a single-ended signal would fail.
It is also a multidrop bus: many devices share one pair of wires, typically in a daisy-chained line topology with termination resistors at each end to prevent reflections, and bias resistors to hold the idle state defined. A classic RS-485 segment supports up to 32 standard unit loads and around 1,200 metres, with the trade-off that speed decreases as distance increases. Only one device transmits at a time, so the higher-layer protocol handles addressing and turn-taking.
By contrast, RS-232 is a point-to-point, single-ended standard limited to short distances and one device per port - fine for a local console but unsuited to field networks. RS-485's multidrop, long-distance, noise-tolerant design is why it became the workhorse for field wiring, carrying Modbus RTU meters, PROFIBUS DP, DNP3 serial, and BACnet MS/TP across pump houses, tank farms, and skids.
In cloud and remote SCADA, serial devices reach the network through a serial-to-Ethernet gateway or an RTU/edge device with RS-485 ports. The gateway terminates the serial link, speaks the field protocol (often Modbus RTU) to the daisy-chained instruments, and forwards data upward over TCP/IP. A cloud SCADA like Merobix reads those serial devices over Modbus - polled locally by an edge gateway and pushed outbound - so legacy RS-485 meters and controllers gain cloud dashboards and historization without being replaced.
No. RS-485 is a physical-layer electrical standard that defines how signals are transmitted on the wire. Protocols such as Modbus RTU, PROFIBUS DP, DNP3 serial, and BACnet MS/TP run on top of the RS-485 physical layer, which handles the differential signalling and multidrop wiring.
RS-232 is single-ended and point-to-point, limited to short cable runs and one device per port. RS-485 uses balanced differential signalling for strong noise rejection, supports multidrop networks of many devices, and reaches roughly 1,200 metres - which is why it dominates industrial field wiring.
Through a serial-to-Ethernet gateway or an RTU/edge device with RS-485 ports. The gateway polls the serial instruments locally using their field protocol (commonly Modbus RTU) and forwards the data over TCP/IP, so a cloud SCADA can read and historize legacy serial devices without replacing them.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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