A VXI based readout system for EUROGAM

Control and readout of the EUROGAM data acquisition system are performed over the VMEbus incorporated in D-size VXI (VME extensions for instrumentation) crates. A crate readout-controller has been developed to read, from acquisition modules within its crate, an event´s data using a single, slightly modified, VMEbus block transfer. Readout controllers buffer the data from several events until they can be transferred, over a cable bus defined for this purpose, to VME-based event-building and parameter histogramming systems. The mechanisms that have been defined permit the data for each physical event to be assembled as a contiguous block within VMEbus memory modules, without any need for prior knowledge of which detectors will produce data for an event. The contribution of the readout system to system dead-time has been minimized by the use of three independent levels of readout, with data buffering incorporated at each level. In addition to assembling data into event blocks, the readout system will concurrently create histograms of the data collected from individual detector-channels.<>