A scan test circuit includes a scan flip-flop that receives a reset
signal, a data signal, a scan data signal, and a scan shift enable signal
selecting either the data signal or the scan data signal. A reset control
circuit controls the reset signal according to the scan shift enable
signal. Even if the reset signal originates in a combinatorial circuit,
the reset control circuit can prevent the flip-flop from being reset
during a scan shift sequence, without the need for external control of
the reset signal. Further control of the reset signal can be provided by
a mask circuit. These reset control features enable improved fault
coverage to be obtained with a reduced number of external input
terminals, a reduced number of test patterns, and only a small amount of
additional test circuitry.