, ▁written ▁by ▁D erek ▁Brown ▁for ▁H ite ch ▁Electron ic ▁Dis plays ▁of ▁Clear water , ▁Florida , ▁communic ates ▁with ▁on board ▁P LC s ▁using ▁two ▁interfaces . ▁The ▁serial ▁interface ▁is ▁used ▁to ▁receive ▁the ▁ 4 ▁character ▁command ▁codes ▁separated ▁by ▁spaces ▁to ▁sign ify ▁the ▁end ▁of ▁each ▁command . ▁The ▁N ID A Q ▁( National ▁Inst rument ▁Data ▁Ac quisition ) ▁card ▁was ▁used ▁to ▁provide ▁status ▁back ▁to ▁the ▁P LC s . ▁There ▁are ▁ 8 ▁opt ically ▁isolated ▁status ▁channels . ▁One ▁channel ▁was ▁used ▁to ▁provide ▁a ▁heart be at ▁signal ▁to ▁tell ▁the ▁P LC ▁that ▁the ▁software ▁is ▁on ▁and ▁function ing . ▁The ▁file ▁formats ▁were ▁un com pressed ▁AV Is ▁passed ▁through ▁a ▁mask ing ▁filter ▁to ▁put ▁the ▁pixels ▁in ▁the ▁sp ots ▁for ▁the ▁countries . ▁ ▁During ▁the ▁first ▁two ▁minutes ▁of ▁the ▁show , ▁the ▁Earth ▁glo be ' s ▁LED ▁screens ▁were ▁off . ▁It ▁was ▁brown ▁in ▁color , ▁but ▁invisible ▁in ▁the ▁thick ▁black ▁of ▁the ▁night . ▁The ▁Earth ▁Glo be ' s ▁LED ▁screens ▁turned ▁on ▁in ▁part ▁two ▁of ▁the ▁show , ▁showing ▁imag ery ▁of ▁the ▁natural ▁world ▁and ▁icon ic ▁man - made ▁structures . ▁S light ly ▁fewer ▁than ▁ 3 0 0 ▁pictures ▁appeared ▁on ▁the ▁Glo be ' s ▁spher ical ▁video ▁screen ▁during ▁the ▁show . ▁Century ▁III , ▁an ▁Or lando ▁area ▁film ▁company , ▁edited ▁the ▁video ▁portion