For a complete PLC, its components include:

1. Power supply
2. Input IO port
3. Output IO port
4. CPU
5. RAM/ROM, etc.

Among them, the power supply is responsible for providing power support to the equipment, and the more common specification is 9-30VDC. The input IO port is responsible for collecting digital or analog signals, digital signals are PNP/NPN input signals, counter signals, etc. The analog input IO signal is divided into current analog input IO signal, voltage analog input IO signal, temperature analog input IO signal, pressure analog input IO signal and so on.

The output IO is responsible for the output and communication of PLC control commands, and it is also divided into two categories: digital and analog. Digital output IO is divided into two types: PNP or NPN output, and analog output IO is divided into current analog output, voltage analog output, relay analog output, pulse analog output, etc.

The CPU, also called the central processing unit, is responsible for the execution and calculation of the PLC control program. It is the core and brain of the PLC system.

RAM and ROM are the program storage locations of the PLC, you can call them random access memory and read only memory.