After all VXI crates the DT32 bus passes through a histogrammer unit which is a VME module acting as a spy onto the data. The unit is software programmable to select any specific parameters from any choosen detectors and build histograms via direct memory increment into global dual port memory.

The histograms can be examined using any of the workstations to check the quality of the data and monitor detector performance.

Additionally by histogramming the control tokens generated by the readout system (for example the start event token and end subevent tokens) the histogrammer can be used as a very powerful hardware diagnostic tool.

Currently there are 32 Mbytes of histogramming memory but this can be increased by adding more memory cards into the VME crate.

The DT32 bus histogrammer can only histogram data which is part of a multi-parameter event. In order to obtain "true" singles it is necessary to histogram data based on the detection of an event by the CFD of the detector channel in the Ge VXI card. See next page.