99% AC test coverage using only LBIST on the 1 GHz IBM S/390 zSeries 900 Microprocessor

This paper explains a new logic built-in self-test (LBIST) technique used in production on the zSeries 900 microprocessor and associated cache chips. LBIST is a test technique critical to the S/390 suite of tests. Various improvements have been made over successive generations of S/390 part numbers. New for the '00 design is the programmable selection of weights during LBIST. This is a comprehensive paper covering why we wanted to improve LBIST, how we improved it, choices made in implementing the enhancement and the results. The results include both the improved LBIST fault coverage and a discussion of the empirical fallout data showing the effectiveness of this technique in production. In addition, we include an example showing added benefits of the new technique.