A system, apparatus and method of isolating a plurality of limiting
logical cones in a chip during a logical built-in self test (LBIST) are
provided. An LBIST is performed on the chip in order to locate a first
latch that fails the test. Particularly, latches on the chip are arranged
in a plurality of scan chains wherein each latch holds data for a logical
cone. The LBIST is performed on one scan chain at a time. Once the first
latch is located, a first limiting cone (i.e., the cone for which the
first latch is holding data) may be isolated. After isolating the first
limiting cone, the data from the first latch is masked out and the LBIST
is repeated on the scan chain. The data is masked out in order to
facilitate the identification of any other latch that may fail the test.
Again, if another latch fails the test a corresponding limiting cone may
be isolated.