Product introduction: · PLC adopts the method of executing user program in cycle. OB1 is an organization block (main program) for cyclic processing, which can call other logic blocks or be interrupted by an interrupt program (organization block).

·After the startup is completed, OB1 is continuously called cyclically, and other logic blocks (FB, SFB, FC or SFC) can be called in OB1.

• Cyclic program processing can be interrupted by certain events.

During the processing of the cyclic program, the CPU does not directly access the input address area and output address area in the I/O module, but accesses the I/O process image area inside the CPU (in the system storage area of the CPU)