End horiz retrace      index 05h  CRTC  protected

Layout  b7    EHB   End horizontal blanking bit 5
        b6-b5 HRD   Horizontal retrace delay (??)
        b4-b0 EHR   End horizontal retrace

- EHB (bit 7)
        Bit five of the six-bit End horiz blank.

- HRD (bits 6-5)
        ??

- End horizontal retrace (bits 4-0)
        The five-bit value used to determine the end of the horizontal
        retrace period.