Any planar liquid crystal cell, asymmetric with respect to the middle plane parallel to the boundary plates, presents an electro-optical response dependent both on the amplitude of the external electric field and on its polarity. Pixels of commercial passive liquid crystal matrix correspond to symmetric cells and hence their electronic multiplexing schemes are not suitable to address matrices composed of asymmetric pixels. All known bistable nematic cells present a kind of asymmetry, and new multiplexing schemes have to be developed. Here we show how the polar and the dielectric couplings in bistable nematic cells can be used to perform novel effective waveforms.