RS-485 is a standard for serial communication that specifies the electrical characteristics of balanced differential signaling over long distances. It is an improvement over the older RS-232 standard, offering greater range, higher data rates, and better noise immunity, making it well-suited for industrial and commercial applications where reliable communication over long distances is required.

Key features of RS-485 communication include:

1. Differential Signaling: RS-485 uses differential signaling, where data is transmitted as voltage differences between two lines (A and B), rather than with respect to a single ground reference. This allows RS-485 to provide better noise immunity and longer communication distances compared to single-ended signaling standards like RS-232.

2. Multipoint Communication: RS-485 supports multi-drop or multipoint communication, allowing multiple devices to share the same communication bus. Each device on the bus has a unique address, and communication occurs in a half-duplex mode, meaning that devices can transmit and receive data, but not simultaneously.

3. Long Communication Distances: RS-485 can support communication distances of up to 1200 meters (about 4000 feet) at data rates up to 100 kbps, depending on factors such as cable quality and environmental noise. With lower data rates, longer communication distances are possible.

4. Higher Data Rates: RS-485 supports higher data rates compared to RS-232, typically ranging from 100 kbps to 10 Mbps, depending on the implementation and cable quality.

5. Master-Slave Configuration: RS-485 communication often utilizes a master-slave configuration, where one device (the master) initiates communication with one or more slave devices. This allows for centralized control and coordination of communication on the bus.

6. Half-Duplex Communication: RS-485 communication is typically half-duplex, meaning that data can be transmitted and received, but not simultaneously. Devices on the bus must take turns transmitting and receiving data, using mechanisms such as polling or token passing.

RS-485 is commonly used in industrial automation, building automation, process control, access control, and other applications where robust, reliable communication over long distances is required. It is also used in applications such as RS-485 Modbus networks, which are widely used for connecting programmable logic controllers (PLCs), sensors, actuators, and other industrial devices.