RS485 Communication
RS485 is a differential serial communication standard commonly used for reliable communication over longer distances and in electrically noisy industrial environments.
What is RS485?
RS485 (EIA-485) defines the electrical characteristics of drivers and receivers for serial communications. Its differential signaling inherently rejects common-mode noise, which is crucial when routing cables near high-voltage industrial equipment.
How We Use It
- Industrial Sensor Networks: Connecting dozens of sensors distributed across a facility.
- Modbus Physical Layer: Providing the hardware foundation for Modbus RTU communications.
- Multi-Device Communication: Creating primary/secondary (master/slave) networks for coordinated control.
- Long-Distance Wiring: Enabling data transmission where standard I2C, SPI, or single-ended UART would fail.
Technical Details
We design RS485 interfaces utilizing robust transceivers with built-in ESD protection. Our hardware designs ensure proper bus topology (daisy-chaining rather than star), implement selectable termination resistors, and calculate optimal fail-safe biasing to maintain a known state when the bus is idle. On the firmware side, we implement precise timing control for driver enable pins (DE/RE) to avoid bus collisions.
Frequently Asked Questions
How far can RS485 communicate?
Under ideal conditions with proper cable and termination, RS485 can reach up to 1,200 meters (4,000 feet) at lower baud rates.
Why is termination needed?
Termination resistors (typically 120 ohms) are required at both ends of the bus to prevent signal reflections that cause data corruption.
How many devices can be on one RS485 bus?
Standard RS485 drivers support 32 devices, but modern fractional-load transceivers can support up to 256 devices on a single bus.
Is RS485 half-duplex or full-duplex?
RS485 can be wired as half-duplex (2 wires) or full-duplex (4 wires). We most commonly use half-duplex for industrial multi-drop networks.
What's the difference between RS485 and Modbus?
RS485 is the physical hardware layer (the wires and voltages), while Modbus is the software protocol (the language) running over those wires.