Question:
Why should the main program PLC_PRG not be renamed or deleted?
Answer:
PLC_PRG is a special predefined block for a cyclic task. This block is called exactly once per control cycle. PLC_PRG is generally the main program in a Single_task program.
If Project --> Insert object is executed for the first time after a new project was created, the default input in the dialog box block is a block named PLC_PRG, type program. You should not change this default input!
If other tasks have been defined in the project, the PLC_PRG block is not absolutely essential because then the execution sequence depends on the task allocation.