The High Resolution Energetic X-Ray Imager (HREXI) CZT detector development program at Harvard is aimed at developing tiled arrays of finely pixelated CZT detectors for use in wide-field coded aperture 3-200 keV X-ray telescopes. A pixel size of $simeq$ 600 $mu m$ has already been achieved in the ProtoEXIST2 (P2) detector plane with CZT read out by the NuSTAR ASIC. This paves the way for even smaller 300 $mu m$ pixels in the next generation HREXI detectors. This article describes a new HREXI calibration facility (HCF) which enables a high resolution sub-pixel level (100 $mu m$) 2D scan of a 256 $cm^2$ tiled array of 2 $times$ 2 cm CZT detectors illuminated by a bright X-ray AmpTek Mini-X tube source at timescales of around a day. HCF is a significant improvement from the previous apparatus used for scanning these detectors which took $simeq$ 3 weeks to complete a 1D scan of a similar detector plane. Moreover, HCF has the capability to scan a large tiled array of CZT detectors ($32cm times 32cm$) at 100 $mu m$ resolution in the 10 - 50 keV energy range which was not possible previously. This paper describes the design, construction, and implementation of HCF for the calibration of the P2 detector plane.
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