RS-485

A differential twisted-pair serial standard, resistant to noise and usable over long cable runs, common for motors and servos.

RS-485 (formally TIA/EIA-485) is a physical-layer standard for serial communication, sending a differential signal (read as the voltage difference between two wires) over a twisted pair; it resists electrical noise well, can run over distances up to a kilometer or more, and lets multiple devices share a single bus, usually in half-duplex mode (only one side can transmit at a time). It only defines the electrical characteristics; common higher-layer protocols riding on top of it include Modbus RTU or a vendor's own proprietary protocol. In robots, many servos, joint motors, electric grippers, and sensors use RS-485. Its weakness is a lower data rate than EtherCAT or CAN FD, and it relies on a master polling each device in turn, which becomes a bottleneck once a robot has many joints running at a high control frequency.

ExampleAn electric gripper commonly runs the Modbus RTU protocol over RS-485, with the host computer sending open/close commands through a USB-to-485 adapter.

Also called

EIA-485, TIA-485

Related

Controller Area Network / CAN with Flexible Data-Rate · EtherCAT (Ethernet for Control Automation Technology) · Servo (Smart Serial Bus Servo) · Servo Drive / Motor Driver · Unitree GO-M8010-6 Motor

Sources

RS-485 - Wikipedia