Working principle of upper and lower computers

The host computer is a computer that people can directly issue control commands to, usually a PC, and various signal changes (hydraulic pressure, water level, temperature, etc.) are displayed on the screen. The slave computer is a computer that directly controls the equipment to obtain the equipment status, usually a PLC/single-chip microcomputer. The command issued by the host computer is first given to the slave computer, and the slave computer then interprets the command into the corresponding timing signal to directly control the corresponding equipment. The slave computer reads the equipment status data (usually analog) from time to time, converts it into a digital signal and feeds it back to the host computer. In short, the actual situation varies greatly, but the essence remains the same: both the upper and lower computers need to be programmed and have a dedicated development system.

In concept

The controller and service provider are the host computers

The controlled and served are the lower machines.

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

But the upper and lower computers can be converted

How it works

How the two machines communicate generally depends on the lower computer. TCP/IP is generally supported. However, the lower computer generally has a more reliable unique communication protocol. When you buy a lower computer, you will get a lot of manual CDs that tell you how to use the unique protocol to communicate. There will be a lot of examples in it. Generally, for programmers, it is just that simple at first glance, using some new APIs. Multi-language support function modules generally support several high-level languages ​​for upper computer programming at the same time.

Usually, the communication between the host computer and the slave computer can adopt different communication protocols, such as RS232 serial communication or RS485 serial communication. When the computer and PLC communicate, not only the traditional D-type serial communication can be adopted, but also the two-wire PROFIBUS-DP communication which is more suitable for industrial control can be adopted. The communication between PLC and the host computer can be realized by using the packaged program development tool. Of course, you can write the driver interface protocol to control the communication between the host computer and the slave computer.

Usually, industrial computers, workstations, and touch screens are used as host computers, and communication control PLCs, microcontrollers, and other lower computers are used to control related equipment components and drive devices.