Abstract: A system, method, and computer program product for scan testing a device under test (DUT). In one embodiment, compressed test data comprising packets are received at a serial test data input. The packets contain encoded data characterizing a test data bit stream and each includes a bucket select field and a fill value field. The bucket select field contains an bucket select value that maps to a length of a bit-string. The fill value field contains a fill value indicating the uniform binary value of the bit-string. The compressed test data is then expanded and the expanded test data is scanned into internal structures of the DUT to test internal structures of the DUT. In a preferred embodiment, the compressed test data is received at a first clock rate. The test data is expanded and scanned into the internal structures of the DUT at a second clock rate that is higher than the first clock rate.