Scan compression has emerged as the most successful solution to solve the problem of rising manufacturing test cost. Compression technology is not hierarchical in nature. Hierarchical implementations need test access mechanisms that keep the isolation between the different tests applied through the different compressors and decompressors. In this paper we discuss a test access mechanism for Adaptive Scan that addresses the problem of reducing test data and test application time in a hierarchical and low pin count environment. An active test access mechanism is used that becomes part of the compression schemes and unifies the test data for multiple CODEC implementations. Thus, allowing for hierarchical DFT implementations with flat ATPG.