Three common communication methods of PLC - Mitsubishi

A PLC network consists of multiple subnets. The communication process of each subnet is determined by the communication protocol. The communication method is the core content of the communication protocol. The means of communication include visit control and data transmission. What are the three common communication methods of PLC?

Three common communication methods of PLC - Mitsubishi

1. Cyclic I/O communication form

Periodic I/O is generally used for long-distance I/O in the form of communication PLC. The I/O links in a link operate as primary. The PLC long-distance I/O host is the master station, and all I/O equipment of other long-distance stations is the slave station. The master station is equipped with a "long-distance I/O buffer" and a mailbox structure is selected. It is divided into several sub-boxes, with one sub-box for each slave. Each subbox is divided into two grids, one for sending and the other for acceptance. The master station communication processor selects the periodic scanning method, communicates data with each slave in turn, sends the grid data sent by the corresponding sub-box to the station, and the slave reads the data and puts it into the receiving grid of the corresponding sub-box. In this way, the primary "long-distance I/O buffer" is refreshed periodically.

2. Overall I/O communication form

The overall I/O communication form is the communication form of serial shared memory area, which is mainly used for communication with the PLC in the link area communication form.

The principle of communication in the form of big picture I/O is shown above. Each I/O area of each PLC in the PLC network is divided into a link area, and each link area is structured as an e-mail. The same number is sent to the same area as the receiving area and occupies the same address area. One is the sending area and the other is the receiving area. Communication via broadcasting. The data of the PLC1 transmission area is broadcast on the PLC network of the top transmission area. After receiving the data, PLC2. The PLC3 stores the data in their respective acceptance area No. 1

3. Master-slave bus communication method

The main bus communication form, also known as the 1:N communication form, refers to the bus structure PLC subnet with N stations, of which only one master station and the others are slave stations.

1:N communication form uses centralized visit control technology to distribute bus visits, and generally uses the method of round table meeting. The so-called round-robin checklist is a list of slave number sequences configured in the master. The master station queries the slaves according to the order of the inspection table to check whether the bus is used to achieve the intention of allocating the bus usage rights.

For sites with high real-time requirements, the slave number can appear in the wheel martyrdom table multiple times, giving the site a higher communication priority. In some 1:N communications, the polling table approach is combined with the abort approach. Urgent tasks can abort normal cycle polling to gain priority.

Token bus communication, also known as token bus communication N:N communication, refers to the fact that there are N stations in the same condition on the PLC subnet of the bus structure, which have nothing to do with the master and slave. It can also be said that N sites are masters.

There are two forms of data transmission at the site where the token is obtained, i.e., the non-response data transmission form and the response data transmission method. When the non-response data transmission form is selected, the station that obtains the token can immediately send the data to the intent station and complete the communication process after the transmission is completed; When the data transmission method with response is selected, the station that obtained the token does not complete the communication after sending data to the intent station. As long as the intent station obtains the token and sends the corresponding frame to the sending station, the entire communication process can be completed. The echo time of the latter increases significantly, and the real-time performance decreases.

4. Communication method of the main station of the floating station

The communication form of N:M communication is suitable for the PLC network of bus structure, that is, there are M stations on the bus, including M stations. N(N

The N:M communication form adopts the visit control technology that combines the token bus and the master-slave bus. First of all, N master stations form a logical ring. Through the token flow in the logical loop, the bus usage rights are scattered between N masters, which is the meaning of floating masters. The master station that has obtained the bus access will decide which stations to communicate with during its token holding time according to the master station's method. The master station is generally equipped with a polling table, which can be based on others

What are the three common communication methods of PLC? Data transmission with the FX3U, FX2N, FX2NC, FX1N, FX0N programmable manipulators can be built on an N:N basis. Using this network communication, they can link data in a small-scale system.

Three common communication methods of PLC - Mitsubishi

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