Maximal multiple fault coverage using single fault test sets

In this paper, an analysis based on the sensitization structure behavior in the existance of multiple faults for the general class of combinational circuits is presented. The analysis is based on partitioning the set of primary inputs into three subsets S/sub e/ (excitation set), S/sub p/ (persistency set), and S/sub c/ (control set). The problem of augmenting a single fault test set to obtain a maximal multiple fault coverage is formulated as the one of maximizing the number of primary inputs in the S/sub c/ set (or minimizing the number of primary inputs in S/sub p/) It is shown that this analysis can be used in extending single fault test sets in order to achieve a maximal multiple fault coverage. We have presented a procedure for augmenting any single fault test set. An experiment has been carried out on the 74LS181 ALU using twelve single fault test sets. It is shown that different fault classes can be covered using the procedure presented in this paper. A 100% double fault coverage for all the single fault tests is achieved.