TRANSLATING UNRESTRICTED RELAY LADDER LOGIC INTO BOOLEAN FORM

Single-pass translation of unrestricted relay ladder logic (RLL) into an AND/OR Boolean form is described. A data representation of the ladder is specified for supporting computer-aided entry and flow displays, as well as the translation. The representation separates downward and upward vertical flow channels to simplify interpretation. The vertically separated representation can be derived during interactive keyboard entry of the model, without placing added demands on the user. The translation algorithm is explained in structured pseudocode and with a series of graphic translation examples. A dynamic data structure is given for the target AND/OR tree form. Algorithmic descriptions are done in the readable syntax of Modula-2, with pseudocode in place of specialized constructions.