There are two high-density headers fitted to the underside of the daughterboard. These headers, designated HDRX, J1, and HDRY, J2, route the signal and power interconnect to the motherboard and to the other daughterboard site. See the an243_revx.ucf constraints files, available in application note AN243, Example LogicTile Express 3MG design for a CoreTile Express A5x2.