What is the connection between RS-485 and Modbus?

What is the connection between RS-485 and Modbus

　　 RS-485 is a physical interface, in simple terms, it is hardware. RS-485 belongs to wired transmission, so hardware transmission medium is needed. In fact, two wires are enough. The two wires transmit the same signal, but the transmitting end divides the signal into two. The receiving end will restore it to the original signal.

　　 The difference between RS-485 and RS-232

　　 RS-232 also requires two wires, and a ground wire must be added to communicate, so it is three wires. We don't care about the ground wire. Of the remaining two wires, one is sending and the other is receiving. Both sending and receiving can be regarded as data cables.

　　 The third wire is the ground wire. There is no clock wire on the hardware, but the communication parties have agreed on the baud rate in advance before they can communicate normally (it can be regarded as the clock frequency). Asynchronous serial communication is named after it.

RS-485

　　 Because RS-485 has the advantage of a differential transmission line, it can cancel the interference introduced by the signal in the transmission process, but the receiving end of RS-232 cannot. Therefore, RS-485 has stronger anti-interference ability and can transmit signals up to kilometers, while RS-232 can only transmit more than ten meters.

　　RS-485/Modbus is a popular way of network layout, which is characterized by simple and convenient implementation. The RS485 conversion interface is relatively cheap and has a wide variety of types.

　　What is Modbus?

　　 Modbus is an international standard communication protocol used to exchange data between devices of different manufacturers (usually for industrial purposes). The so-called agreement can also be understood as the "language" mentioned above, which belongs to software.

　　 Modbus is just a kind of communication protocol, just like Chinese and English, it is a language of communication, a language of communication between machines.

　　 The connection between RS-485 and Modbus

Under normal circumstances, two devices transmit data through the Modbus protocol. RS-232 was first used as the hardware interface (that is, the serial communication port (serial port) on an ordinary computer); later, RS-422 was also used, and the most commonly used RS-485, this kind of interface has a long transmission distance, which is more used in industrial scenes.

　　 Modbus protocol is divided into three modes: Modbus RTU, Modbus ASCII and Modbus TCP later developed. The physical hardware interfaces used by the first two are serial (Serial) communication ports (RS-232, RS-422, RS-485).

　　 Modbus TCP is to conform to the development trend of today's world. It can be connected by Ethernet or Internet to transmit data. So it is also called Modbus TCP mode. The hardware interface of this mode is the Ethernet port, which is the network port generally used on our computers.