Why Crates?

1. Why Crates? Dave Doughty 7/23/03 Hall D Electronics Review

2. Plays to our Strengths/Experience • JLAB has lots of experience with crates • Successful deployment of large crate system in Hall B • CODA handles this nicely • JLAB has built numerous complex boards • Trigger supervisor – all three halls • Trigger for Hall B – level 2 uses FEE backplane for communication • F1 TDC • JLAB has experience with distributed pre-amps • Hall B – 35,000 pre-amps • Some pain involving deterioration/access/replacement • Hall D Electronics group is fairly small

3. Simplifies Trigger Design • Boards in crates leads naturally to “crate sums” of energy, tracks • Use backplane for passing board sums to “crate summer” • If backplane exists – why not use for data concentration at the ROC? • Each calorimeter crate of ~256 channels needs 4 fiber links for trigger • Distribution of L1 Trigger signal (for hit/energy/feature extraction) is simpler

4. Simplifies DAQ/CODA Design • Architecture of Hall D with crates is essentially that of Hall B • Slightly larger in crate count • CODA needs minimal changes • Handle event blocking • ROC-FEE change • Handle distributed event building • Managing crates and ROC doesn’t change

5. Simplifies Power/Mechanical • Only power to run all over is pre-amp power • Low power • Heavy-duty power (think FADC) now has tens of endpoints rather than thousands • Mechanical support is automatic • Except pre-amps which are light and small

6. Simplifies ADC/TDC Development • F1 TDC developed for current use at JLAB will work with very minor modifications for Hall D • Flash ADC development in VME or CPCI will be easier to test/debug