Partially detectable faults in synchronous sequential circuits

Faults in sequential circuits are studied. Undetectable and redundant faults under different modes of operation are analysed. Undetectable faults are split into two classes: operationally redundant faults and partially redundant faults. Operationally redundant faults are defined as faults that are never manifested as faulty output during normal operation. Partially redundant faults are defined as faults that can affect the output sequence under certain initial conditions otherwise it is undetectable. Faults in sequential circuits are, accordingly, classified into three classes: detectable, partially detectable and operationally redundant. Test generation strategies and the relation between test sequences under different modes of operation are analysed.