The ALICE central trigger system

The ALICE trigger system is situated in the experimental cavern and has a centralized layout: the central trigger processor (CTP), the sub-detector interface (local trigger unit) and the TTC partitions are all installed in adjacent racks. The CTP generates three levels of hierarchical hardware triggers - LO, LI and L2. At any time, the 24 sub-detectors of the ALICE experiment are dynamically partitioned into up to 6 independent clusters. The level of event pile-up is controlled by the past-future protection logic. The local trigger unit (LTU) serves as a uniform interface between the CTP and the sub-detector readout electronics. In the stand-alone mode of operation, the LTU fully emulates the CTP protocol. An overview of the ALICE central trigger system will be presented, with the emphasis on the design of hardware modules