On the Replacement of Scan Chain Inputs by Primary Input Vectors

We show that the functionality of scan chain inputs sometimes exists in a circuit as part of its functional operation, and can be exhibited by applying specific primary input vectors. By relying on such functionality it is possible to hide scan chains as part of a solution that addresses security. It is also possible to reduce the number of external scan chain inputs that need to be added to the circuit as part of the scan implementation, or remove the need to multiplex primary inputs as scan chain inputs. We define inherent scan in functions to capture the functionality of scan chain inputs that exists in a circuit, and show that they can be computed effectively by simulation. We address the case where multiple scan chains are to be used for the circuit