The EUROGAM trigger system

EUROGAM was designed for gamma ray spectroscopy and the simplest mechanism for event detection is to count the number of coincident gamma rays detected in the array which gives a figure of merit to each event. The EUROGAM detector array uses the XIV backplane system for front-end electronics including triggering and readout. The main tasks of the trigger system are described. The trigger system is distributed with an intelligent local trigger in each of the detector electronics channels. Novel aspects of the system are the use of XIV lines to generate and to distribute trigger signals and the distributed nature of the system to allow efficient parallel and pipelined operation with low system dead times. Throughout the design of the trigger system the various design proposals were tested against a few difficult triggers devised by the physicists who intend to use the system. As an example, one of the simpler triggers is considered.<>