code: function(mode, wid, name, type, units, data)
         {
            var padded4 = (data.length + 3) >> 2;
            var pad = Buffer.alloc( (padded4<<2) - data.length);
            var format = 'CCSLLLCxxxLaa';
            var requestLength = 6 + padded4;
            var dataLenInFormatUnits = data.length / (units >> 3);
            return [format, [18, mode, requestLength, wid, name, type, units, dataLenInFormatUnits, data, pad] ];
         }
docs: mode: 0 replace, 1 prepend, 2 append format: 8/16/32