Central Trigger Control System (TCS)

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  • 8 FinOR 8 L1A
  • Partition Controller 8 DAQ Partitions
  • Throttle Logic
  • STATUS Signals from FMM
  • IO Tracker Emulator
  • Counters: deadtime, etc.


The central Trigger Control System (TCS) has two main tasks

  • It controls the L1A (Level-1 Accept) rate and limits it if necessary
  • It provides control signals for all readout and trigger crates

To achieve the first task, the TCS receives status information from the readout electronics as well as from the Data Acquisition System (DAQ) and trigger electronics via the so-called Trigger Throttling System (TTS). The front-end readout electronics uses a synchronous TTS (sTTS), the DAQ an asynchronous TTS (aTTS). However, due to the limited size of the subdetector buffers and because of the non-negligible signal propagation time between different parts of the experiment, in the case of some of the subsystems this is not sufficient. Therefore, local state machines (emulators) are used to emulate the occupation of the front-end buffers of individual subsystems. When a subsystem is not ready to accept triggers, they may be either delayed or temporarily inhibited. In this way it is possible to guarantee that triggers are distributed according to well-defined rules specifying the maximum admissible instantaneous and average rates of L1A signals, and thus to minimize the danger of buffer overflows in subsystems. In addition, the system monitors and records the dead time of the various subsystems.

The second main task of the TCS is to provide not only the distribution of L1A signals to all subsystems, but also to deliver special control signals for reset commands, calibration purposes, and tests (BCRES [bunch crossing zero], resynchronization and reset commands,L1RESET and other so-called BGo or control commands). These signals are distributed via the Trigger, Timing and Control (TTC) network of the CMS experiment.

Thus, the functions of the TCS are to

  • limit the trigger rate, according to programmed Trigger Rules, based on
    • signals from subsystems
    • signals from subsystem emulators
  • generate and distribute control signals
  • generate calibration and test trigger sequences
  • monitor the dead time of all subsystems

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