Results are reported from a beam test of prototype silicon microstrip detectors and front-end electronics developed for use in the LHC detector ATLAS. The detector assemblies ("modules") were 12 cm long and were read out with binary electronics. Both irradiated and unirradiated modules were measured in a 1.56 T magnetic field for efficiency, noise occupancy, and position resolution as a function of bias voltage, binary hit threshold, and detector rotation angle with respect to the beam direction.