RS485busser

RS485busser refers to networks and devices that operate on the RS-485 standard for serial communications. RS-485 defines the electrical characteristics of a balanced differential signaling system that allows several devices to share a single pair of wires in a multipoint topology. The arrangement is common in industrial and building automation due to its robustness and long reach.

A typical RS-485 bus uses two wires (two-wire half-duplex) or four wires for full-duplex, carried on a twisted pair. Each node has a transceiver that can drive or listen on the bus; multiple devices may be connected in a daisy-chain along the same pair. The bus is usually driven by one transmitter at a time, with higher-level protocols such as Modbus RTU or Profibus coordinating access. To minimize reflections, termination resistors (commonly 120 ohms) are placed at both ends of the main trunk, and biasing resistors establish a defined idle state. Nodes must release the bus when not transmitting; star-shaped topologies are discouraged in favor of linear layouts.

Standard RS-485 supports up to 32 drivers and 32 receivers on a single bus segment, though modern networks may use repeaters or switches to extend reach or device count. Data rate and distance trade-offs: higher speeds shorten the maximum cable length, while longer cables work at lower speeds. This makes RS-485 suitable for long-range communication in electrically noisy environments.

Applications include industrial controllers, building management systems, energy metering, and process instrumentation. RS-485 is a physical layer standard; the choice of protocol (for example Modbus RTU, BACnet MS/TP, or DMX512) determines addressing, timing, and data framing.