The 2nd level trigger system of the HADES detector

The multi-level trigger system of the HADES detector is intended to select dilepton events in heavy ion reactions and to reduce minimum bias event rates by a factor of 10000. After a first level trigger based on the charged particle multiplicity the second level is the essential dilepton trigger which identifies electron signatures in several detector components and correlates them to dileptons. The third level trigger verifies these dilepton candidates using additional tracking information. Programmable logic devices, FPGAs and CPLDs, as well as DSPs are widely used to gain flexibility and provide common solutions. The trigger concept and fully functional versions of the readout boards and the second level trigger are presented.