 The first pair of cells will stay latched until the second pair of cells gets latched and so forth.In this way, data flow direction is controllable through clock zones

Wire-crossing in QCA cells can be done by using two different quantum dot orientations (one at 45 degrees to the other) and allowing a wire composed of one type to pass perpendicularly "through" a wire of the other type, as shown schematically in figure 8.The distances between dots in both types of cells are exactly the same, producing the same Coulombic interactions between the electrons in each cell.