Understanding RS485

RS-485 is a standard communication interface, RS (Recommended Standard) recommended standard meaning, 485 is the identification number.

RS-485 uses two(Twisted-pair cable is generally used in the long-distance transmission of differential signals, differential transmission is a signal transmission technology, and the traditional practice of a signal line and a ground line is different, differential transmission in the two lines have a signal transmission, the amplitude of these two signals are the same, the phase of the opposite, then the transmission of signals in the two lines of the signal is a differential signal. The signal receiver compares the difference between the two voltages to determine the logic state sent by the transmitter.)The bus wiring is widely used for data acquisition and industrial control, and one of its main advantages is that it allows multiple RS485 devices to be placed on the same bus.

specificities

Transmission distance: RS485 theoretically the farthest communication distance is 1200 metres, if the distance is more than 1200 metres, you can use the 485 repeater (extender) to extend, theoretically the farthest can be extended to 3000 metres.

High speed: RS485 data transmission rate can reach 10Mbps, but if it is transmitted over long distances, the rate will be reduced to ensure signal quality.

Multi-device access: RS485 interface allows up to 32 (in some cases up to 256) devices to communicate on the same bus.

Communication mode: half-duplex(Half duplex, or Half duplex Communication, means that at any point in the communication process, information can be transmitted both from A to B and from B to A, but only one transmission exists in one direction, not both. Like full duplex transmission, half duplex consists of a bi-directional line (the line can pass data in both directions), and with half duplex, the transmitter and receiver at each end of the communication system, which are relayed to the communication line by a receive/transmit switch, switch directions, and, therefore, incur time delays)communication mode (at the same moment, only one party can send or receive, both parties cannot send or receive at the same time) or multi-point communication (one-to-many).

Differential Signal Transmission: RS485 uses differential signals for data transmission (two twisted pairs of wires, A and B, to transmit the signal), which can effectively suppress common mode interference.(Common mode interference current size is not necessarily equal, but the same direction (phase). Electrical equipment external interference is mostly common mode interference, external interference is also mostly common mode interference, common mode interference itself is generally not harmful to the equipment, but if the common mode interference is transformed into a differential mode interference, the interference will be serious, because the useful signals are differential mode signals)Improved noise immunity.

Supported protocols

Modbus RTU: Modbus is a widely used industrial communication protocol, Modbus protocol is simple, easy to implement, mostly used for data acquisition and control between industrial equipment.

Profibus-DP: It is a bus system for industrial automation, more suitable for high-speed, real-time control applications. Support a variety of devices connected, commonly used in complex industrial automation environment.

CANopen: is a CAN (Controller Area Network) bus based on the application layer protocol, in some cases can also be achieved through the RS485. It supports distributed real-time control applications and is used more in the automotive field.

DeviceNet: A fieldbus standard used in automation, developed by Allen-Bradley, with a high market share in the U.S. The DeviceNet protocol supports a wide range of device types, including sensors, actuators, and controllers.

Ethernet/IP: Industrial Ethernet Protocol, the IP in the name is short for Industrial Protocol, not Internet Protocol. It provides high-speed data transmission capability and supports communication between a variety of industrial equipment.

DNP3: A communication protocol designed for power systems, the DNP3 protocol supports a variety of communication media, including RS485, and is suitable for secure and highly reliable power automation and remote monitoring systems.

DLT645: DLT645 protocol is mainly used for energy meter data acquisition, and is also the most commonly used and simplest communication protocol for meter acquisition, refer to DLT645 protocol - PV meter data acquisition.

CC-Link: an open fieldbus network protocol, supporting a variety of industrial equipment, can use RS485 interface.