The TSC sits in the calorimeter backbeam area adjacent to the FECs. It has 8 current inputs (4 left and 4 right) and generates 4 outputs. The cables from the FEC to the TSC are the same length throughout the FCAL, BCAL and RCAL. The only major exception is additional cable length added to compensate for faster tubes used in the FCAL EMC towers. The result is that the groups of FCAL, BCAL and RCAL TSCs receive their signals within 2 nsec of each other.
Each TSC output consists of two amplifiers each driving one half of a shielded twisted pair cable in differential mode. The TSC sums left and right FEC sums for each trigger tower to produce two sums (EMC and HAC) for each of two towers containing EMC and HAC sections. The TSC produces up to four separate HAC sums for towers without EMC sections. In order to facilitate special combinations of HAC cells in those FCAL and RCAL regions which are shadowed by BCAL EMC towers, the TSC has internal jumpers that can be used to combine up to all eight of its inputs to generate a single output. In practice, up to six inputs are combined. In these cases, one or more of the four output channels are unused. In most locations, two input channels are summed in one output channel. However, in regions of complex geometry, the TSC is used to directly combine the left and right sides of two HAC (four inputs) sections in a single output sum.