last update: 050131
The trigger maintains two-way communication with RHIC through the RHIC rack in the DAQ room.
The RS signal acts as the STAR Trigger heartbeat. We use the coincidence of the BRB and YRB in the trigger to eliminate beam-gas interactions. These signals come to STAR via two V124 VME units in the RHIC rack. Each V124 unit has 8 channels. We control the programming of the V124 units via the PET (Parameter Editing Tool) provided on the RHIC workstation in the control room. Channel 1 in each V124 is reserved for a copy of the RS signal, so it is programmed to output every 3rd click of the RF strobe. Note that each ring contains 360 buckets but that at most 120 are filled. It is this 1/3 filling factor that set the RS to be 1/3 of the RF strobe.
The MCR will tell us which of the Yellow and Blue buckets are full and we will then transfer this information to the second channel of the V124 units to give us the BRB and YRB signals.
NOTE: One of the tricky aspects of trigger setup is synchronizing the RS with our CDB ADC gates and synchronizing the BRB and YRB signals for the correct crossing. This is done via computer settable delays in the V124 units.