Answer: CPU is the core of PLC and acts as a nerve center. Each PLC has at least one CPU. It receives and stores user programs and data according to the functions assigned by the PLC system program. It collects the status or data sent by the field input device by scanning and stores them in the specified register. At the same time, it diagnoses the working status of the power supply and PLC internal circuits and syntax errors in the programming process. After entering the operation, it reads instructions one by one from the user program memory, and after analysis, it generates corresponding control signals according to the tasks specified by the instructions to command the relevant control circuits.
The CPU is mainly composed of an arithmetic unit, a controller, registers, and data, control and status buses that realize the connection between them. The CPU unit also includes peripheral chips, bus interfaces and related circuits. Memory is mainly used to store programs and data and is an indispensable component of PLC.
From the user's point of view, it is not necessary to analyze the internal circuit of the CPU in detail, but there should be enough understanding of the working mechanism of each part. The CPU controller controls the CPU operation, which reads, interprets and executes instructions. But the working rhythm is controlled by the oscillation signal. The arithmetic unit is used to perform digital or logical operations and works under the command of the controller. The register participates in the operation and stores the intermediate results of the operation. It also works under the command of the controller.
CPU speed and memory capacity are important parameters of PLC. They determine the working speed, I/O quantity and software capacity of PLC, thus limiting the control scale.
