The Hall A data acquisition uses CODA (CEBAF Online Data Acquisition), a toolkit developed at Jefferson Labs by the data acquisition group. General information is available separately from that group or on the web in an obvious link from the Jefferson Lab web site. We are currently using CODA version 1.4.
We have one fastbus crate in the electron spectrometer and two fastbus crates in the hadron spectrometer. The fastbus modules are of the following types: (1) LeCroy model 1877 TDCs operating in common-stop with 0.5 nsec resolution for our drift chambers and straw chambers; (2) model 1875 TDCs operating in common-start with 0.1 nsec resolution for our scintillators and trigger diagnostics; and (3) model 1881M ADCs for signals from scintillators, Cerenkov, and leadglass detectors. Event-driven readout of our beam current and position monitors will be available from VME systems.
The trigger supervisor is a custom-made module built by the data acquisition group. Its functions are to synchronize the readout crates, to administer the deadtime logic of the entire system, and to prescale various trigger inputs. It has several other capabilities which we don't use. We have two trigger supervisors, one in each spectrometer. This allows us to run the spectrometers independently if needed, and to switch between one or the other for coincidence mode; generally the spectrometer which is slowest should have the active trigger supervisor in order to reduce the required delay.
Use the ``adaq'' account for running CODA and other online software. The directory tree of an experiment is adaq/$EXPERIMENT. The software for our online diagnostics, scaler display, and offline data analysis will be described in separate subsections below. The trigger management software is described in the trigger chapter.