Central processing unit (CPU)

Central processing unit (CPU)

The central processing unit (CPU) is the control center of PLC. It receives and stores the user program and data input from the programmer according to the function given by the PLC system program, checks the status of power supply, memory, I / O and alarm timer, and can diagnose syntax errors in user program. When the PLC is put into operation, it first receives the status and data of each input device in the field by scanning, and stores them into the I / O image area respectively. Then, it reads the user program one by one from the user program memory. After the command is interpreted, the logic or arithmetic operation is executed according to the instruction, and the result is sent to the I / O image area or data register. After all the user programs have been executed, the data in each output state or output register of the I / O image area are finally transmitted to the corresponding output device, which runs in a cycle until it stops running.