Patent US 5,377,315

A method is provided for the regeneration of process control flow diagram for a programmable logic controller programmed using function blocks. It includes the steps of decompiling object code of a program of the controller to generate a listing of data concerning functions of the programmed controller, logic blocks implemented by the programmed controller, and connections and any operating parameters of those logic blocks; identifying logic blocks representing external inputs and outputs of the programmed controller; establishing a sheet data file and making it a current sheet data file; tracing and tabulating function blocks and their connections successively from each external output back towards the external inputs while placing data relative to the function blocks and their connections in the current sheet data file, eliminating duplicated entries; monitoring the amount of data placed in the sheet data file, and, whenever the amount of data in the current sheet data file reaches a level that inclusion of further data would result in overcrowding if represented on a single drawing sheet, establishing an additional sheet data file which replaces, as current sheet data file, the sheet data file last established; including, each time an additional sheet is established, in the last established and additional sheet data files respectively, input and output references respectively for connections between function blocks tabulated in the two sheet data files; scanning the data placed in the sheet data files to locate duplicated output references and removing those references from the sheet data files; and individually converting each sheet data file into a drawing file by calculating and adding, based on the content of that sheet data file, data as to location of function blocks and connection lines within a sheet to which that file relates, and descriptive data as to content of that sheet.