Experience with the first level trigger of H1

H1 is a high energy physics experiment at the electron proton collider HERA at DESY, routinely taking data since 1992. Calorimetric and tracking systems record the properties of the particles produced in the collisions in a total of 270000 electronic channels. The collision frequency of 10.4 MHz necessitates pipelining of all data in the centrally clocked trigger and front end readout systems. This report outlines the architecture of the trigger and data acquisition system and describes the experience gained in the first years of running the experiment. A crucial aspect is the clock phase adjustment and stability of all trigger signals.<
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