Ethernet (Ethernet) is a kind of LAN communication technology. The IEEE 802.3 standard of IEEE has established the technical standard of Ethernet. It specifies the content of the connection including the physical layer, electronic signal and medium access layer protocol. Ethernet uses twisted pair as the transmission medium, and can cover a range of up to 200 meters without relaying. The most popular Ethernet type data transmission rate is 100Mb/s, and the updated standard supports 1KMb/s and 10KMb/s.
The biggest advantage of Ethernet technology is that it is the most popular LAN technology at present, and has gradually replaced other LAN standards such as Token Ring, FDDI and ARCNET. Nowadays, the Internet that we are familiar with refers to the network that covers the whole world after all these large and small LANs are connected together.
2. Serial communication technology
Serial port is a very common interface for communication between devices. It is also widely used for communication between devices and instruments. Common serial ports are RS-232 (using 25-pin or 9-pin connectors) and half-duplex RS-485 and full-duplex RS-422 for industrial computer applications.
Serial communication uses serial communication, that is, serial port sends and receives byte sequences in bits. Typically, serial ports are used for ASCII character transmission. Serial communication is done using 3 wires: ground, transmit and receive. Serial communication can receive data with the receiving line while transmitting data using the transmission line. It is simple and can communicate over long distances, and its communication length can reach 1200 meters.
The biggest point of serial communication is the high penetration rate. The serial port PC is still standard. Up to now, in order to facilitate the connection of printers, most industrial devices have serial ports. Those devices without serial ports are commonly connected through serial ports during their development. On the computer for development, the serial port is the easiest and easiest way for the device to communicate.
It is also worth mentioning that if you do not consider the cable connected to the serial port, the cost of serial communication is very low.
The networking capability of serial communication is poor. Although it is usually more stable than wireless, in industrial environments, it is also susceptible to communication instability caused by the electromagnetic environment of the cable, and even the serial port burnout. The communication speed of the serial port is still quite different from that of Ethernet. Generally speaking, it is only suitable for low-rate and small-data communication.
Unlike the previous communication technologies, Modbus is generally considered to be an application layer protocol standard that uses serial communication. It does not contain electrical specifications. Modbus was originally published by Modicon in 1979 for communication using programmable logic controller (PLC). Later, Modbus RTU, Modbus ASCII and Modbus TCP were derived. The first two physical interfaces used are the serial ports described above. The latter uses the Ethernet interface.
With the wide application of PLC in the industrial field, Modbus has become the most popular communication protocol in the industrial field. It uses Master/Slave communication, which is a one-to-many connection. One master controller can support at most. 247 slave controllers