RS485 is a widely used standard for serial communication, particularly in industrial and commercial environments. Here's a structured overview:

​Basics
​Standard: Developed by the Electronic Industries Alliance (EIA), RS485 defines the electrical characteristics of a serial communication system.
​Purpose: Designed for robust, long-distance data transmission in noisy environments.
Key Features
1. Differential Signaling:

Uses two wires (A and B) to transmit data via voltage differences, enhancing noise immunity.
Voltage Range: Typically ±5V, with a minimum detectable difference of ±0.2V.
2. Multi-Drop Capability:

Supports up to ​32 devices on a single bus (expandable to 256 with repeaters).
​Topology: Bus or daisy-chain configuration.
3. Duplex Modes:

​Half-Duplex: Two-wire setup (communication in one direction at a time).
​Full-Duplex: Four-wire setup (rarely used; RS422 is more common for full-duplex).
4. Distance and Speed:

​Maximum Distance: Up to ​1,200 meters (4,000 feet) at lower speeds.
​Data Rates: Ranges from 100 kbps (long distances) to 10 Mbps (short distances).
5. ​Noise Immunity:

Rejects common-mode noise due to differential signaling, making it ideal for industrial settings.
​Technical Considerations
​Cabling: Twisted-pair cables with 120Ω characteristic impedance.
​Termination: 120Ω resistors at both ends of the bus to prevent signal reflections.
​Biasing: Resistors may be added to stabilize the idle state in half-duplex systems.
​Applications
Industrial automation (e.g., PLCs, sensors).
Building automation (HVAC, security systems).
Protocols like ​Modbus RTU, Profibus, and DMX512.
​Comparison with RS232
​RS232: Point-to-point, shorter distances (<15 meters), single-ended signaling, prone to noise.
​RS485: Multi-drop, longer distances, differential signaling, noise-resistant.
​Key Notes
​Protocol Agnostic: RS485 defines only the physical layer; data protocols (e.g., Modbus) handle addressing and messaging.
​Addressing: Devices are identified via software protocols, not hardware.
​Common Misconceptions
​Full-Duplex: While possible with four wires, RS485 is typically half-duplex. RS422 is the full-duplex counterpart.
​Speed vs. Distance: Trade-offs exist; higher speeds reduce maximum cable length.
RS485 remains a cornerstone of reliable serial communication in demanding environments, balancing distance, speed, and robustness.