On Modifying Logic Networks to Improve Their Diagnosability

This paper considers the use of control logic to reduce the number of tests required by a logic network and to simplify test generation. The properties of EXCLUSIVE-OR (EOR) circuits as control elements are examined. Systematic procedures are presented for modifying any combinational or sequential network so that the resulting network requires only five tests. These tests can easily be generated using a set of predefined test patterns of length five. The design of diagnosable networks using a limited amount of control logic is also discussed.