Hello everybody,

I want to know if there are systematic methods which can be to develop cause & effect diagram from the PLC control program. Thanks in advance

 

Try drawing state diagrams or grafcet diagrams (SFC). Generally what you find when you try to create these after the fact however is that the original program was complex and convoluted and doesn't fit these very easily. It usually works much better to create the diagrams first and then write the PLC program to fit them.