Multiple fault detection in two-level multi-output circuits

It is often stated that in irredundant two-level logic circuits, a test set for all single stuck faults will also detect all multiple stuck faults. We show by a simple example that this result does not hold for multi-output circuits even when each output function is prime and irredundant. Using a result from the programmable logic array technology, we give an output ordering constraint that, if satisfied during test generation, will make a single stuck fault test set a valid multiple stuck fault test set for irredundant two-level multi-output circuits.