Fault Analysis and Test Generation for Programmable Logic Arrays (PLA´s)

Programmable logic arrays (PLA´s) are the logic implementation vehicle for many applications. Due to their regular structure, one is able to model and analyze many more of the likely physical faults than the conventional stuck faults considered for random combinational logic implementations. We investigate shorts between the lines and crosspoint defects (spurious absence or presence), as well as stuck faults in a PLA. It is shown that a complete crosspoint test set also detects most of all faults analyzed. The crosspoint-oriented test set is compact, easy to generate, and technology-invariant. For the test generation, the regularity of the PLA structure is utilized for ease of computation and for test set optimality. Groups of crosspoint defects are sensitized simultaneously. For each such fault group, a test configuration which contains the totality of the tests for the faults under consideration is efficiently generated. When the configuration is empty, there exists no test that detects the particular group of faults. A covering set of tests is then selected from the configuration. Our test generation method (TPLA) uses two basic and effective heuristics; they are the initial word ordering for processing and the use of look-ahead merit function whenever there is a free choice of values in a test input variables.