Scan Insertion
Hello, Scan insertion is the process of converting the flip flops present in a circuit into scan flip flops The flip-flops in the circuit, shown in Figure, are connected together in a chain to form a shift register, also called scan chain. This makes all flip-flops in the circuit controllable and observable leaving behind only the combinational logic to be tested. During scan mode, the test vectors are shifted into (scan-in) the scan chain by shift operations. The test vectors are then applied to the combinational logic and the response is clocked back into the flip-flops. The response is then shifted out (scan-out) from the scan chain to test as the next test vector is being scanned in. This DFT converts the difficult to test sequential circuit into a fully combinational circuit. For large designs, the long chain is split into several smaller chains in order to cope with the large number of test patterns. The chains can have different lengths and the depth is define...