Don't-care identification on specific bits of test patterns

Given a test set for stuck-at faults, a primary input value may be changed to the opposite logic value without losing fault coverage. One can regard such a value as a don't-care (X). The don't care values can be filled appropriately to achieve test compaction, test data compression, or power reduction during testing. However, these uses are better served if the don't cares can be placed in desired/specific bit positions of the test patterns. In this paper, we present a method for maximally fixing Xs on specific bits of given test vectors. Experimental results on ISCAS benchmark circuits show how the proposed method can increase the number of Xs on specific bits compared with an earlier proposed method.