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 rvec pp → pK+rvec Y (Y = Λ, Σ0 or Y*) reaction and vector meson production (ψ, 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 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