A method and apparatus are provided for performing on-board, in-circuit,
and/or wafer level scan-based testing of integrated circuits. With the
apparatus and method, one or more sequential storage elements, e.g.,
flip/flops, are coupled to combinational logic and are configured to have
an additional port for receiving a scan mode signal. The scan mode signal
sets the sequential storage element into one of two modes of operation:
static mode in which the sequential storage element's output does not
change on a falling edge of a scan enable signal or a transitional mode
in which the sequential storage element's output is permitted to change
on the falling edge. With sequential storage elements configured in this
manner, a configuration scan is performed to set certain ones of the
sequential storage elements into a static mode and other sequential
storage elements into a transitional mode. A test pattern is then applied
to the sequential storage elements and a pattern capture cycle is
commenced.