A parallel decompressor capable of concurrently generating in parallel multiple portions of a deterministic partially specified data vector is disclosed. The parallel decompressor is also capable of functioning as a PRPG for generating pseudo-random data vectors. The parallel decompressor is suitable for incorporation into BIST circuitry of ICs. For BIST circuitry with multiple scan chains, the parallel decompressor may be incorporated without requiring additional flip-flops (beyond those presence in the LFSR and scan chains). In one embodiment, an incorporating IC includes boundary scan design compatible with the IEEE 1194.1 standard. Multiple ones of such ICs may be incorporated in a circuit board. Software tools for generating ICs with boundary scan having BIST circuitry incorporated with the parallel decompressor, and for computing the test data seeds for the deterministic partially specified test vectors are also disclosed.