The ATLAS Level-1 Central Trigger Processor (CTP)

The ATLAS Level-1 Central Trigger Processor (CTP) com- bines information from the Level-1 calorimeter and muon trig- ger processors, as well as from other sources such as calibration triggers, and makes the final Level-1 Accept deci- sion. The CTP synchronises the trigger inputs from different sources to the internal clock and aligns them with respect to the same bunch crossing. The algorithm used by the CTP to com- bine the different inputs allows events to be selected on the basis of trigger menus. The CTP provides trigger summary information to the data acquisition and to the Level-2 trigger system, and allows one to monitor various counters of bunch- by-bunch as well as accumulated information on the trigger inputs. The design of the CTP with its six different module types and two dedicated back-planes will be presented.