Direct Computation of LFSR-Based Stored Tests for Broadside and Skewed-Load Tests

Abstract

Using both broadside and skewed-load tests for delay faults provides a higher fault coverage and more compacted test sets. An earlier work showed that it is possible to share input test data between broadside and skewed-load tests, and thus reduce the input test data volume. This article develops an algorithm for computing stored tests that can be used for applying both broadside and skewed-load tests in the context of a specific test data compression method. Under this method, a programmable linear-feedback shift register is used for on-chip decompression. In the stored test data, a stored test consists of a seed and two primary input vectors. The seed determines the scan-in state of the applied broadside or skewed-load test as well as the additional scan-in vector required for a skewed-load test. In the algorithm developed in this article, stored tests are computed directly without first computing broadside or skewed-load tests. This avoids situations where the tests cannot be compressed or do not have common input test data.