There are three communication methods for plc, namely: 1. Signal line connection, which is the simplest way, that is, connecting signal lines between devices such as microcontrollers or touch screens and PLC; 2. Free port Communication; 3. ModBus communication, this method uses the ModBus protocol for communication.
#The operating environment of this tutorial: Windows 10 system, Dell G3 computer.
How many communication methods are there for plc?
Three common communication methods of plc
PLC = Programmable Logic Controller, a programmable logic controller, an electronic system for digital operation, designed for use in industrial environments Designed. It uses a type of programmable memory to store programs internally, perform user-oriented instructions such as logical operations, sequence control, timing, counting and arithmetic operations, and control various types of machinery through digital or analog input/output. or production process. PLC communication methods mainly include RS232, RS485, PPI/MPI, PROFIBUS DP/PA/FMS field bus, Ethernet bus, DEVICEnet bus, and wireless network and other communication methods.
There are many plc methods, and many manufacturers have their own unique ones, such as Schneider's MB; AB's DH, CONTROLNET; Siemens' PROFIBUS, MPI; and many general ones. For example, RS232, RS485, Ethernet, GPRS, etc.
1. Signal line connection
This is the simplest way, that is, to connect the signal line between the microcontroller or touch screen and other equipment and the PLC. The input of the PLC is connected to the output of the microcontroller; PLC The output is connected to the input of a microcontroller. This is the most common way. In this way, the PLC can be connected to almost any industrial control device, such as servo systems, frequency converters, robots, etc.! The disadvantage is that if too many signals need to be transmitted, Then the number of cables will be very large, and once the cables are damaged, it will be very difficult to maintain!
2. Free port communication
We have talked about free port communication many times before, and we have specifically explained it ASCII code, friends in need can go to my previous articles to find it, I won’t repeat it today.
3.ModBus communication
The third method is to use the ModBus protocol for communication.
The main communication method is 485 communication, followed by 422, 232, and CAN bus communication. Assume that one of the plcs is the host computer and the others are slave computers. Set different station numbers for interactive communication.
Under normal circumstances, if you do not need to read too many parameters, you can also use the touch screen. All PLCs communicate with the touch screen, and then switch control through the touch screen. PLC communication mainly uses serial asynchronous communication, and its commonly used serial communication interface standards include RS-232C, RS-422A and RS-485.
RS-232 and RS-422, when communicating with the host computer, it means the PLC communicates with the computer. If the transmission distance is less than 16 meters, you can directly use the serial port RS-232. If the transmission distance is greater than 16 meters, you must use PS-232. /RS-422 converter converts it to RS-422 and then connects it to the computer. The RS-232 interface has a low data transmission rate, limited transmission distance, and poor anti-interference ability. RS-422 uses a full-duplex communication method and differential transmission method to enhance its anti-common mode interference ability. There is also RS-485, which is an improvement on RS-422. The difference between them is that RS-485 uses a half-duplex communication method.
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