The upper computer refers to the computer that people can directly send control commands, generally PC, and display various signal changes (hydraulic pressure, water level, temperature, etc.) on the screen. The lower computer is the computer that directly controls the equipment to obtain the condition of the equipment, generally PLC / SCM and so on. The command sent by the upper computer is first given to the lower computer, and then the lower computer interprets the command into the corresponding time sequence signal to directly control the corresponding equipment. The lower computer reads the equipment status data from time to time (generally analog quantity), converts it into digital signal and feeds it back to the upper computer. In short, the actual situation is very different, but the changes are inseparable: the upper and lower computers need programming, and there are special development systems.


The controller and service provider are the upper computer

The controlled and served are the lower computers

It can also be understood as the relationship between host and slave

But the upper computer and the lower computer can be converted

working principle

How to communicate between two computers generally depends on the lower computer. TCP / IP is generally supported. But the lower computer generally has a more reliable unique communication protocol. When you buy the lower computer, you will bring a lot of manual CDs to tell you how to use the unique protocol communication, which will give a lot of examples. Generally speaking, for programmers, it’s just like that, using some new APIs. Multi language support function module, generally support several high-level languages for PC programming at the same time.

Usually, different communication protocols can be used for communication between upper computer and lower computer, such as RS232 serial port communication or RS485 serial communication. When using computer and PLC to communicate, not only the traditional d-form serial communication can be used, but also the dual line PROFIBUS-DP communication which is more suitable for industrial control can be used, The communication between PLC and host computer can be realized by using the encapsulated program development tool. Of course, you can write your own interface protocol to control the communication between the upper computer and the lower computer.

Generally, industrial control computer, workstation and touch screen are used as upper computer, communication control PLC, single chip microcomputer and other lower computers, so as to control the relevant equipment components and driving devices.

Editor in charge: LQ

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