Abstract: An integrated circuit includes a plurality of internal devices that are tested by setting the states of their data registers to respective levels, first forming a known initialization value and then a functional data value. All the data registers used for testing are coupled as one or more shift registers and by clocking data through a serial scan path, test stimuli can be shifted in and results shifted out. The scan path connections are provided in addition to the usual functional operation signal connections. During functional operation, the data transitions in the scan path signals are disabled to reduce the power dissipation associated with driving the scan path signals.