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The specific relationship between the data programmed into the memory cells and the threshold voltage levels of the memory cell depends on the data encoding scheme used for programming the memory cells. In one example, a gray code scheme may be used to assign data values to the threshold voltage distribution curves. "Gray code encoding" refers to a type of encoding scheme based on a numbering system that assigns a certain bit values to a range of threshold voltages that a memory cell may have. The bit values are assigned such that the bit pattern differs between adjacent threshold voltage ranges by only one bit. Such a bit pattern assignment is advantageous because while a threshold voltage may change, drift, from one range to a neighboring range, unintended change or drift is likely not enough to cause a two bit change in the encoding. In this manner, undesired drift can be detected and accommodated.

Added by DJM 12 2021