  The Level-2 Silicon Track Trigger preprocessor (L2 STT) of the D0 detector in
Run II is described. It performs a precise reconstruction of charged particle
tracks in the Central Fiber Tracker (CFT) and the Silicon Microstrip Tracker
(SMT). Events with displaced tracks originating from the decay of long living
particles such as B hadrons are triggered on. The presence of b quarks
contained in such hadrons is relevant for B physics and crucial as signature of
top quark and Higgs boson decays.
