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The Detector Memory System

The Detector Memory System allows detector data to be collected, displayed and transferred to the system computer. A detailed description of the system is given by Johnson 1986 (RGO Electronics Report 413, the Detector Memory System) and this will not be repeated here.

Essentially, the DMS is a purpose-built computer, with a large area of memory for storage of detector data. The system is based on the industry-standard VME architecture. There is a high speed data interface (DICI; Dual IPCS CCD Interface) between the detectors and the VME memory. The system also has an image display facility, based on an Opal Graphics Controller.

After each exposure, the data from all detectors appears in memory in the Detector Memory System (DMS). Images obtained with CCD detectors are read out into the DMS at the end of an exposure; for a full-frame read-out this can take several minutes. Photon counts from the IPCS-2 are continually transferred to the DMS during an exposure, where they are built up into an image. All data are displayed on a dedicated monitor as they arrive.

The DMS is capable of handling multiple detectors simultaneously, reading the data from different detectors into different areas of memory (normally referred to as buffers). This feature is particularly important for the operation of ISIS.

Once the data is in the DMS, it can be transferred to the Sparcstation for quick evaluation, or it can be transferred to the system computer for archival to tape. It is also possible to display images on the DMS, and carry out some basis data-analysis functions; however, with the introduction of the SPARCstation it is expected that these DMS functions will be used less frequently.