The DISTO first level trigger at SATURNE

The DISTO collaboration has built a large-acceptance magnetic spectrometer designed to provide broad kinematic coverage of multi-particle final states produced in pp scattering. The spectrometer has been installed in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the p&oarr;p→pK+Y&oarr; (Y=Λ, Σ0 or Y*) reaction and vector meson production (φ, ω, and ρ) in pp collisions. The common signature of such events is the multiplicity of four charged particles in the final state. A flexible 1st level trigger which uses topological information from fast detectors (scintillating fibers and hodoscope) has been built. It is completely software programmable through a menu-driven user interface and allows switching between production and monitor triggers on successive beam spills