RS232 & RS485 Communication Interfaces

Both RS-232 and RS-485 are electrical interface standards for serial communication (physical layer), widely used in industrial control and device communication. Core differences: RS-232 supports short-distance, point-to-point and full-duplex communication; RS-485 supports long-distance, multi-point bus, half/full-duplex communication with strong anti-interference performance.

1. RS-232 Interface

Full name: EIA-RS-232 (Recommended Standard 232)
Positioning: An early standard for point-to-point short-distance communication.

• Signal mode: Single-ended signal (TX/RX referenced to GND)

• Electrical level & logic:
Logic 1: -3V ~ -15V
Logic 0: +3V ~ +15V

• Transmission mode: Full-duplex (sending and receiving simultaneously)

• Transmission distance & baud rate:
Max distance: ≤ 15 meters
Max baud rate: About 115.2 kbps

• Wiring: Minimum 3 wires (TXD, RXD, GND)

• Connector: DB9 (9-pin) / DB25

• Advantages: Simple, universal, full-duplex

• Disadvantages: Short transmission distance, weak anti-interference, only one-to-one connection

• Application scenarios: PC serial ports, debugging ports, old instruments, short-distance devices

2. RS-485 Interface

Full name: TIA/EIA-485-A
Positioning: Mainstream in the industry, supporting long distance, multi-node and strong anti-interference.

• Signal mode: Differential signal (judged by voltage difference of A/B twisted pair)

• Electrical level & logic:
Logic 1: A > B (voltage difference > +200mV)
Logic 0: B > A (voltage difference < -200mV)

• Transmission mode: Half-duplex (2 wires by default) / Full-duplex (4 wires)

• Transmission distance & baud rate:
Max distance: 1200 meters @ 100 kbps
Max baud rate: 10 Mbps (short distance)

• Wiring: 2 wires (A+ / B-) + GND

• Connector: No standard (terminal block, DB9, RJ45 commonly used)

• Advantages: Long transmission distance, strong anti-interference, multi-point bus (one master and multiple slaves, up to 32/128 nodes)

• Disadvantages: Transmit-receive switching required for half-duplex, relatively complex protocol

• Application scenarios: Industrial PLC, sensors, inverters, building automation, power monitoring

3. Core Comparison


4. Selection Guide

Choose RS-232 if:

• Short distance (within several meters)

• Only two devices connected directly

• Full-duplex (simultaneous sending and receiving) is required

• Old devices / PC serial communication

Choose RS-485 if:

• Long distance (tens to thousands of meters)

• Multi-device networking (multiple devices on one bus)

• Industrial environment (strong electromagnetic interference)

• Long-distance sensors, PLC and inverter networking