We propose a delay test methodology for general sequential circuits. To test a combinational path between two flip-flops, the source flip-flop is initialized to the appropriate value, followed by creation of a transition, which is propagated through the path. An incorrect logic value is captured in the destination flip-flop if the path delay exceeds the clock period. The state of the destination flip-flop is observed at a primary output through path sensitization. Only one vector that propagates the transition through the path is applied with the rated clock period. All other vectors use a slow speed clock to ensure fault-free initialization and fault effect observation. The test generation method uses a 13-value algebra that represents the relevant transition and hazard states of signals. Since several path delay faults can be activated by the vector applied at the rated clock, only the flip-flops with hazard-free steady values are assumed to have deterministic states. This allows us to generate sequentially robust tests. We present the results of the test generation method on ISCAS benchmark circuits.
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