BES III TOF trigger sub-system

The trigger system of Beijing Spectrometer III (BES III) is in charge of choosing interested physics events from mass data to compact to the extent that data acquirement system (DAQ) can deal with. The Time-of-Flight (TOF) trigger system, consists of a 9U_size VME TOF trigger module, a VME plug-in rear transmission module, is one of the sub systems of BES III. The sub-system is required to receive 272 scintillators hit information via 28 fibers, while it virtually owns the capability to receive 368 bits scintillators hit information signals via 34 fibers. According to the physical requirement, the TOF trigger module yields the 7 bits trigger information signals, and passes them to the Global-Trigger-Logic in real time, where the primal trigger signal L1 will be generated. It also sends 136 bits position information signals to the Track-Match-Logic in real time for the particle flight tracks processing. All these information are transmitted by the rear transmission module. In additional, all the packaged valid events data are available to the DAQ system through VME64 bus in CBLT mode. All the trigger logic algorithms are carried by 9 Altera EP1K30 and 1 EP1S40 FPGAs (Field Programmable Gate Array) on the TOF trigger module. Compared to traditional design, the employment of high capacity FPGAs ensures the reconfigurable character of the sub-system, provides the advantage of online modification and upgrading in future. During the test after the assembly of the whole BES III system, the TOF trigger sub-system works steadily and efficiently.