Hall B

The CLAS detector in Experimental Hall B consists of almost 40000 instrumented channels interfaced to 19 FASTBUS and 5 VME crates. It is, by an order of magnitude, the largest DAQ system implemented using CODA at Jefferson Lab. It is of similar (or even greater) scale than the proposed Hall D detector. Typical ``high'' running rates in Hall B are 2.5 $\,$kHz and 10 MBytes/s. Readout latency for the front-end crates run between 60 to 200 $\mu$s. Crates holding the TOF high resolution TDCs (Lecroy 1872) not only have the longest readout latency but also the highest conversion deadtime (around 50 $\mu$s), hence they drive both the DAQ rate limitations as well as the deadtime for the system. In tests where these crates were dropped from the system, they were able to achieve rates up to 7 $\,$kHz to tape. The DAQ system for CLAS would certainly benefit from the development of a pipelined high resolution TDC.