A method and apparatus are provided for enhanced Logic Built in Self Test
(LBIST) diagnostics. First multiplexers are respectively coupled between
adjacent sequential channels of a plurality of sequential channels under
test. Each of the first multiplexers selectively receives a first data
input in a first scan mode with the sequential channels configured in a
common scan path and a second data input in a second scan mode with each
the sequential channels configured in a separate scan path responsive to a
first control signal. A first multiple input signature register (MISR)
including multiple MISR inputs is coupled to a respective one of the
plurality of sequential channels under test. A blocker function is
configured for blocking all MISR inputs except for a single MISR input
receiving the test data output of the last sequential channel responsive
to a recirculate control signal. A second MISR shadow register is coupled
to the first multiple input signature register.
