The 4400 module is a modular design that combines the various functional units of a PLC into building blocks that can be combined according to different needs. The 4400 programmable logic controller is a digital operation electronic system designed specifically for application in industrial environments. It adopts a programmable memory that stores instructions for executing logic operations, sequential control, timing, counting, and arithmetic operations internally. It controls various types of mechanical equipment or production processes through digital or analog input and output. When the programmable logic controller is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution, and output refresh. Completing the above three stages is called a scanning cycle. During the entire operation period, the CPU of the programmable logic controller repeatedly executes the above three stages at a fixed scanning speed.