There are two main communication methods of PLC, namely parallel communication method and serial communication method. Let’s explain the two communication methods respectively. If you need to know about serial port and parallel port, please read this article “The Difference between Serial Port and Parallel Port”.
plc serial communication
Serial communication is a data transmission method based on binary bits. Only one bit is transmitted at a time. In addition to the ground wire, only one data line is required in one data transmission direction. This line serves as a data line. It also serves as a communication control line. Data and communication signals are transmitted bit by bit on this line. Serial communication requires fewer signal lines, at least two or three lines, and is suitable for long distance situations. Computers and PLCs are equipped with universal serial communication interfaces, and serial communication is generally used in industrial control. Serial communication is mostly used for data communication between PLC and computer and between multiple PLCs.
Serial communication is divided into simplex and duplex according to the direction of information transmission between devices.
Simplex communication can only send or receive data in a single direction. In duplex communication, information can be transmitted in both directions, and each station can both send and receive data.
Duplex mode is divided into two modes: full duplex and half duplex. The sending and receiving of data are transmitted by two or two different groups of data lines respectively. Both parties in the communication can receive and send information at the same time. This transmission method is called full-duplex mode; use the same line or the same group of lines. To receive and send data, both parties in communication can only send data or receive data at the same time. This transmission method is called half-duplex. Half-duplex and full-duplex communication are often used in PLC communication.
plc parallel communication
Parallel communication is a data transmission method in units of bytes or words. In addition to 8 or 16 data lines and a common line, it also requires control lines for data communication. The transmission speed of parallel communication is fast, but the number of transmission lines is large and the cost is high. It is generally used for short-distance data transmission. Parallel communication is generally used within the PLC, such as data communication between PLC internal components, between the PLC host and expansion modules, or between close-range intelligent modules.