Commissioning of the ATLAS Level-1 Central Trigger

The ATLAS Level-1 Central Trigger consists of the Central Trigger Processor (CTP) and the Muon-to-CTP-Interface (MUCTPI). The CTP receives trigger information from the Level-1 Calorimeter Trigger system directly, and from the Level-1 Muon Trigger systems through the MUCTPI. It also receives timing signals from the LHC machine, and fans them out along with the Level-1 Accept (L1A) signal and other control signals to all sub-detectors. From them, it collects BUSY signals in order to throttle the L1A generation. Upon L1A the Level-1 trigger systems send region-of-interest information to the Level-2 trigger system. The MUCTPI and CTP crates are already installed in the ATLAS underground counting rooms with final or close-to-final boards. We present their status and discuss first commissioning steps. Particular emphasis is put on the integration of the Central Trigger with the Muon and Calorimeter Trigger systems, the Level-2 trigger, and the readout part of the different sub-detectors.