A Transformation Method between PLC Ladder Diagrams and Instruction Lists Using Recursive and Stack Algorithms

Abstract

The method of transforming a ladder diagram (LD) and an instruction list (IL) of PLC (Programmable Logic Controller) to each other is investigated in this paper. Firstly, ladder-step is adopted on transforming LD into IL. Ladder-step is divided series or parallel by using recursive algorithm, and then complicated ladder-step can be divided into several simple ladder-steps which can be converted to IL easily. When obtaining simple ladder-steps’ IL, combining them together to get final IL program of complicated LD program. Secondly, on transforming IL into LD, stack algorithm contributes a lot. Scanning IL to generate LD of each instruction block, and then pushing them into stack. Combine LDs in the stack by operating instruction, and then IL is transformed into LD successfully. Finally, in the last part of this paper, we show our PLC software and lower position machine. In addition, this transforming algorithm has already applied in PLC software successfully.