A Transformation Algorithm of Ladder Diagram into Instruction List Based on AOV Digraph and Binary Tree

Ladder diagram (LD) and instruction list (IL) have been widely used in industries as programming languages for PLC (programmable logic controller). The LD is similar to the electrical schematic diagram, and can represent control logic explicitly. However, LD programs can not be executed directly by PLC. On the other hand the IL which is similar to the assemble language can be processed directly by PLC. Thus, it is necessary to study transformation algorithm from the LD to the IL. This paper proposes a transformation algorithm used to transform the LD into the IL for PLC systems. The transformation algorithm uses an AOV digraph to represent the LD program, and then realizes the transformation by postorder traversing binary trees built form the AOV digraph. In this paper, first some basic concepts and data structures in the algorithm are presented. Second, this paper describes main ideas and detailed steps of the transformation algorithm. A transformation example in this paper shows that the proposed algorithm is correct and has practicability