A VME-based readout system for the CMS Preshower sub-detector

The CMS Preshower is a fine grain detector that comprises 4288 silicon sensors, each containing 32 strips. The data are transferred from the detector to the counting room via 1208 optical fibres running at 800 Mbps. This enormous total data flow of about 1 Tbps necessitates a significant reduction in the data volume. For the readout of the Preshower, a VME-based system is currently under development. The main objective of each readout board is to acquire on-detector data from up to 36 optical links, perform online data reduction and pass the concentrated data to the CMS event builder. The principle modules that the system is based on are being developed in collaboration with the TOTEM experiment.