Translating relay ladder logic for CCM solving

Abstract

Relay ladder logic (RLL) continues to be offered in more PLC systems than any other modeling language. Solving large RLL models with array scanning or instruction list interpreter techniques is not feasible in many applications where large amounts of inactive logic are necessary to insure quality control and safety. An improved translation algorithm is described for converting RLL models into model data for the clause counter map (CCM) solver, whose scan time depends on the current scan activity, rather than the size of the control logic.