The Hardware Event Preprocessor for IBIS (HEPI)
HEPI is the interface between the detector plane and the DPE.
The HEPI control electronics is built up with an ASIC (Application Specific Integrated Circiut). During the engineering phase FPGA's (Field programmable Gate Arrays) were used. Due to the required amount of mass memory two PCB were needed to mount all components. They are mounted in a sandwich style.
HEPI functions are related to both detectors and could be split in Housekeeping and Scientific functions.
- PICSIT and ISGRI overall events counter
- PICSIT pixel rate meters
HEPI scientific functions:
- HEPI provides the time synchronisation of PICSIT and ISGRI.
- Scientific event data from ISGRI and PICSIT are sent via high speed lines to HEPI.
HEPI provides the following pre-processing for PICSIT data:
- amplitude correction
- multiple event reconstruction
and for both data types:
- ISGRI and PICSIT time coincidences identification (could be disabled by setting the science function table)
- ISGRI and PICSIT time format change
HEPI routes the ISGRI data through to the DPE. ISGRI and PICSIT events are analysed for time coincidences. In case of a time coincidence HEPI creates a Compton event, that contains the data of the two coincident events.
For PICSIT data there are six different functions in HEPI:
- PICSIT Photon by Photon: an energy bandwidth filter is applied and PICSIT data are routed through to the DPE event by event
- PICSIT Standard Histogram: PICSIT single and double events are put into separate energy histograms
- PICSIT Polarimetry Histogram: PICSIT double events are put into a histogram with energy bins and scattering angle bins (only alternatively to Standard Histogram)
- PICSIT Calibration Histogram: PICSIT single events are put into 511 keV and 1.275 MeV histograms
- PICSIT Spectral Timing: A eight energy channel histogram without spatial resolution over periods of some msec.
- PICSIT Rate meters: counter for each individual pixel
In all scientific sub modes PICSIT calibration histograms are accumulated in HEPI. The set-up command defines the accumulation time. After this time the two HEPI calibration buffers are switched between histogram accumulation and sending data to DPE.
In Diagnostic mode HEPI provides a transparent mode where data from selected detector layers are transmitted without processing.