A calorimeter trigger system for the ISR Axial Field Spectrometer

A fast and flexible trigger processor system designed to run in parallel up to 51 different types of trigger is used in a large hadron calorimeter experiment at CERN-ISR. A very fast data bus connected to 255 10 bit address ECL memory chips allows programmable selection of events according to their topology and energy pattern in less than 150 ns. In addition this system can interrogate two programmable processors (ESOP) to isolate events characterized by a large energy flow in the central drift chamber (<500 mu s). All functions of the trigger processor can be checked externally by a computer through injecting in parallel simulated input signals into various stages of the system. Salient features and performances are discussed. (3 refs).