RS-232, RS-422 and RS-485 compared

Electrical differences, distances, node counts and wiring of RS-232, RS-422 and RS-485 (2-wire/4-wire), with typical pinouts and when to use which.

RS-232, RS-422 and RS-485 define electrical interfaces only; protocols such as Modbus RTU run on top of them.

Comparison

	RS-232 (TIA-232)	RS-422 (TIA-422)	RS-485 (TIA-485)
Signalling	Single-ended, ±3…±15 V	Differential, 1 driver	Differential, multi-drop
Topology	Point-to-point	1 transmitter, up to 10 receivers	Bus, up to 32 unit loads (more with 1/4, 1/8 UL transceivers)
Typical distance	~15 m (lower at high baud)	up to ~1200 m	up to ~1200 m (at ≤ 100 kbit/s)
Wires	TxD, RxD, GND (+ handshake)	2 pairs + GND	1 pair + GND (2-wire) or 2 pairs (4-wire)
Termination	No	At receiver end	At both ends of the bus (≈120 Ω)

RS-232 DB9 (DTE, PC side): 2 = RxD, 3 = TxD, 5 = GND. Two DTE devices need a null-modem (crossed 2–3) cable.
RS-485 labels differ between vendors (A/B, D+/D−, TxD+/−). The Modbus spec calls them D0/D1 with a common; when in doubt, measure idle voltage (B more positive than A in TIA-485 terms) or swap and test.
PROFIBUS DP uses RS-485 on DB9 pins 3 (B, red) and 8 (A, green).

RS-232: short service connections, legacy modems, single devices next to the PC/PLC.
RS-422: one master sending to several receivers or long point-to-point links (some encoders, displays).
RS-485: multi-drop field networks — Modbus RTU, PROFIBUS DP, many proprietary protocols.

Always use a common reference (GND) in RS-485 even though it is differential, and keep the bus as a line (daisy chain), not a star.

Loading the map…

Updated 2026-10-04