BST Glossary

Structure

The Pad Detector in its final setup consists of 64 wedge shaped silicon detectors with 32 sensitive pads each. They are mounted onto four carbon fibre wheels positioned in -z direction of the vertex (that is: 'backward' in H1 coordinate system) in distances between -612mm and -800mm. The sensitive area of each wheel is segmented 16-fold in phi and 8-fold in radius (between 59mm which is closest possible to the beam pipe, and120mm). Thus a single detector covers 22.5 degrees in phi and delivers individual signals of its 8 radial segments. Adjacent detectors in phi are mounted such that no sensitive gap is allowed. Currently only two sectors of the four wheels are equipped with sensors (phi = 0...45° ).

All the sensitive elements of the Pad Detector are read out simultaneously. On a hybrid directly attached to the silicon the signals are shaped and discriminated upon an adjustable threshold. Every four pads of a given radius are then ORed logically. This digital signal is transmitted to a so-called repeater where synchronization to the H1 clock and a 4:1 data compression takes place. This is to reduce the number of cables to the trigger electronics in the trailer.

Synchronization and data reduction are done in field programmable gate arrays, the XILINX chips. Each XILINX processes signals of those four detectors which are placed in succeeding z-positions within the same phi sector and generates from 32 inputs an 8-bit output at each H1 bunch crossing. The XILINX chips are reconfigurable by remote action; thus synchronization schemes, data reduction rules and logic output formats may be altered on demand and even be different in different phi sectors. For the sake of physics analysis a thorough bookkeeping of the changing configurations is mandatory. Therefore each configuration file is registered upon use and given a unique 16bit identifier. Finally 16 XILINXs will be operated; their configuration files taking approx. 64kByte.

The BST Pad frontend electronics is linked to the trailer by two bunches of cables: one for Slow Control and Powering, the other for Trigger Control and Trigger Data. See the complete cabling layout.

In the BST Slow Control Crate a Macintosh driven Slow Control System is housed. It handles powering of the detectors and the repeater, controlling and measuring the system performance, configuring the XILINX chips. It consists of two double-width PDS (Power Download Station) modules, commercial CAN/IEEE bus drivers, a digital I/O interface and a separate modular Hewlett Packard Power Supply. Slow control is steered from a LabView panel running on the BST Mac (Frame B21 right in room 307 of the Hall North). Also the BBL3 system hardware interface of the BST is located in this rack.

The BST pad data as generated by the repeater are transmitted to the so called TriggerCard in the BST STC crate. This module receives the logic output of four repeaters, thus two Trigger Cards are required in total. The Trigger Card passes information to the PQZP pipelined DAQ system (Store Card) and to the MasterCard where trigger bits for the level 1 trigger of H1 are generated. The Store Card holds a pipeline for the full XILINX output of all repeaters and up to 32 recent bunch crossings. Those data are provided to the DAQ at a level 3 trigger. The Master Card introduces a further 16:1 data reduction when merging the 16 sector data to a single 8bit L1 trigger word.

The BST Store Card(s) and the TriggerCard(s) are read out when the Silicon Branch is included in the DAQ and two banks called TSCD and SITR are written. SITR is a record of the XILINX configuration identifier and the TriggerCard status register. TSCD contains for each event the full 2.3 microseconds history of the BST's digital channels, that is 16 Bytes per time slice with BST 1996 version, organized in four 32bit wide 'RAMs'. Look here for the complete channel map.

Back to the Shift Instructions. To the BST site.