Many integrated circuits allow for the ability to specify among one or more optional features. Particular options are the use of inverting or noninverting address inputs, the number of bits in a word, and any number of other features. These options have been implemented in the past by making or not making connections in the metal level. This method has the drawback, however, that the circuit is not testable before the options are specified because the part is inoperative without the metal layer.
USPTO Backgrounds
USPTO Backgrounds