During the first year of running, HERA operated with 10 electron and proton bunches (the design value is 210). This reduced operation was a good match to the initial learning phase of ZEUS. A first level trigger rate of 10-15 Hz was obtained by applying loose calorimeter energy thresholds. The second and third level triggers further reduced the rate to 3 Hz by applying a timing requirement in the rear and forward calorimeters, and by rejecting cosmic-ray events and first level noise triggers. HERA is currently operating in 90 bunch mode and the sophistication of the trigger system has correspondently increased. We anticipate achieving the system design values in the near future.
In summary, the application of transputers to parallel readout, triggering and data acquisition is widely adapted in the ZEUS experiment. Different hardware modules have been built for interfacing transputers to other hardware devices and a variety of transputer network topologies have been employed. Future high energy physics experiments may use, for example, the TMS320C40 DSP or the IMS T9000 transputer for applications similar to those performed by the IMS T400 and IMS T800 series of transputers in the ZEUS experiment. We are using transputers on a large scale (over 620 in total) and the different approaches to the hardware and distributed processing are working in harmony to increase our understanding of the subatomic world.