Patent ID: 7559002

Claim:
A method of simulating integrated circuit performance of a scan ring having a plurality of serially connected latches in a scan chain, said method comprising: 1) starting a scan clock for a functional scan of a scan chain; 2) recording a first “snap shot” of scan ring data; 3) starting a scan ring; 4) shifting the scan ring using the current scan data; 5) stopping the scan clock when said scan ring has been completely shifted and then taking a second “snap shot” of scan ring data; and 6) comparing the first “snap shot” and the second “snap shot;” wherein if the first “snap shot” and the second “snap shot” are not identical; then thereafter locating a broken spot within the scan latches of the scan ring; wherein each latch comprises an L1 latch and an L2 latch, gated by normal function clocks and scan A/B clocks including a scan A clock and a scan B clock; wherein: when said scan A clock is on, shifting scan data into the L1 latch; and when said scan B clock is on, shifting scan data into the L2 latch; and locating a broken chain if the functional scan fails, comprising the steps as follows: 1) comparing the latches to their expected shifted values in every scan of the scan A clock and the scan B clock; 2) saving previous values of each of a plurality of L2 latches; and 3) obtaining a current latch value and comparing it to a previous value of a precedent latch.