Testability conditions for linear sequential arrays

The problem of testing one-dimensional arrays made of sequential cells is addressed. Each cell is modeled as a finite state machine. Test sequence generation is accomplished using the unique input-output sequence method. The single cell fault model is adopted together with a functional model consisting of transition faults. Fault coverage is evaluated with respect to a gate level implementation of the cell. The conditions for controllability, observability and constant testability are defined. The added difficulty for such a testable approach stems from the fact that tests for sequential cells are composed of sequences of inputs instead of a single input combination (as for the combinational case). Guidelines for choosing test sequences which guarantee testability (and whenever possible, constant testability) without modification to the basic cell are introduced