Trigger System is the central control system of the BESⅢ. It collects signals from the different detector electronics systems and uses them to generate the final event acquisition signal L1*. L1* is then distributed to all the electronics systems with fiber and the sub-trigger systems with differential cables. Fig. 1 shows the scheme of the whole trigger system.

  All signals are pipelined in the Trigger System. Signals from all the electronics systems are transported with fiber. The trigger latency is about 6.4 ms. The Trigger System contains the following sub-trigger systems:

  MDC sub-trigger : To deal with signals from the MDC electronics system;

  EMC sub-trigger: To deal with signals from the EMC electronics system;

  TOF sub-trigger: To deal with signals from the TOF  electronics system;

  MU sub-trigger : To deal with signals from the m Identifier electronics system;

  TKM (TracK Match) sub-trigger : To match long track information from the MDC sub-trigger and hits information from the TOF sub-trigger;

  GTL (Global Trigger Logic) sub-trigger: To collect the trigger conditions from the different sub-trigger systems, generate the L1* signal and fan it out.