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CTD Second Level Trigger

The SLT is closely integrated into the CTD readout electronics. The sense wires are read out individually by a FADC system containing 16 channels per board (two cells). A DSP on each FADC board analyses the FADC data to produce, amongst other things, drift times. The drift times are the input data to the SLT. The FADC boards are further grouped into 16 crates of 18 boards each.

To simplify the connections for the first level trigger (FLT) and to exploit parallel processing in the SLT, the CTD will be read out in azimuthal sectors. The chamber is divided into 16 azimuthal sectors and each one assigned to a FADC crate.

High tex2html_wrap_inline798 tracks from the bunch-crossing point are almost radial. The cell information for these tracks will resides in a single sector and hence a single crate. For NC events, 76% of all tracks are contained in two sectors and above a tex2html_wrap_inline798 of 300 MeV/c a track is always contained in two sectors [2]. Thus overlapping sector processors will pick up most of the interesting tracks. We plan on implementing this by passing the information from the edges of adjacent sectors to neighbouring sectors by transputer links between crates.

The CTD SLT will be implemented in an array of transputers forming an interlocking network with the data acquisition system. The SLT transputers will be either T4's or T8's depending on the need for floating point arithmetic.gif The minimal number of transputers is determined by the number of links needed for communication by the SLT, data acquisition system, and monitoring network. We envision SLT local processing being performed on two or more transputers on each FADC readout-controller board (one board per crate). The transputers search for track segments within local cell masks and these segments are matched, along with the adjacent crate segments, to form tracks at a higher level of processing. Figure 1 show the readout controller transputer link connections.

  figure31
Figure 1:   Readout controller transputer link connections.


next up previous
Next: Online Pattern Recognition Up: Segment Finding Previous: Introduction

Douglas M. Gingrich
Thu Mar 28 18:08:05 MST 1996