1. August 20101 VLSI Testing and Verification Shmuel Wimer Bar Ilan University, School of Engineering

2. August 20102 Design for Testability Testability requires design to be: –Controllable: set to 1 and reset to 0 every circuit node –Observable: be able to examine the logic value of any circuit node It reduces testing cost –allows high fault coverage with relatively few test vectors –Essential to silicon debug since probing every node is impossible There are two design for testability (DFT) methods: –Scan-based design –Built-in self-test (BIST)

3. August 20103 Scan-Chain Flip-Flop When scan mode is 0 the D flip-flop behaves in ordinary mode, and input is being read from data-in. When scan mode is 1 input is taken from scan-in. Flip-flop Scan Mode Data-in Q Clock Scan-in 0 1 All the flip-flops are then serially connected from Q to data-in, a giant shift register, spanning the whole chip. In scan mode all the inputs of flip-flops can be set by streaming in their desired values. Similarly, the output of flip- flops can be streamed out.

4. August 20104 FF Combinational Logic Cloud FF Combinational Logic Cloud FF Scan-in Scan-out Inputs Outputs Scan-Chain Connections