A semiconductor chip and method for diagnostic testing of combinational logic in a logic and array system including Logic Built in Self Test (LBIST) diagnostics are provided. The semiconductor chip includes a logic and array system, an LBIST system, a clocking module, and an addressing module. The method for diagnostic testing includes providing an initialization pattern to an array in the logic and array system, applying a diagnostic control setup, and running the diagnostic test. The diagnostic control setup includes firing a clock every diagnostic test clock cycle and selecting an address from a subset of an address space.