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.
HEPI scientific functions:
and for both data types:
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:
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.