Test strategies described in previous chapters relied on two concepts: controllability and observability (C/O). Good controllability makes it easier to drive a circuit into a desired state, thus making it easier to sensitize a targeted fault. Good observability makes it easier to monitor the effects of a fault. Solutions for solving C/O problems include scan path and various ad-hoc methods. Scan path reduces C/O to a combinational logic problem which, as explained in Chapter 4, is a solved probl