Near-optimal tests for classes of write-triggered coupling faults in RAMs

Abstract

This article is concerned with the detection of write-triggered coupling faults and toggling faults (certain double coupling faults) in n × 1 random-access memories (RAMs), where n is the number of one-bit words in the memory. In an earlier article we showed that any functional test that detects all multiple coupling faults must have a length of at least 2n 2 + 3n. Since such a test is prohibitively long, given modern RAM capacities, we study more manageable subclasses of the class of all coupling faults. We show that there exist two hierarchies of fault models corresponding to nested subclasses of toggling faults and coupling faults, respectively, of increasing maximum multiplicities. We then identify optimal or near-optimal tests for two classes of toggling faults and five classes of coupling faults; these tests are of order n or nlog2 n.