A device includes memory cells, reference memory cells, and a sensing unit. The reference memory cells are configured to store first bit data, second bit data, third bit data, and fourth bit data, in which the first bit data and the fourth bit data are configured to be a high logic state, and the second bit data and the third bit data are configured to be a low logic state. The sensing unit is configured to read bit data stored in one of the memory cells according to the first bit data, the second bit data, the third bit data, and the fourth bit data.