Abstract: In this paper we propose a new apparatus for embedding deterministic patterns in pseudo-random sequences, with application to at-speed BIST. We employ an arbitrary length Shift Register driven by a LFSR (LFSR/SR) with the size of the LFSR dependent only on the number of care bits in any test vector. We provide an efficient method to compute positions of bit-patterns at arbitrarily chosen tap configurations in the LFSR/SR sequence. Hence, one can make an optimal choice of test segments (seeds) while taking inherent advantage of don't care bits in test vectors, say corresponding to random pattern resistant faults. The length of the LFSR/SR can be arbitrarily increased to feed several interconnected logic blocks such that all the care bits of any deterministic test vector can be predictably generated without compromising computational efficiency.