Nonvolatile memory and method with state encoding and page-by-page programming yielding invariant read points

A non-volatile memory, comprising:

• an array of memory cells, wherein individual memory cells are each in one of eight memory states, the eight memory states being an erase state and seven programmed states with increasing threshold values across a threshold window;
• a group of data latches for storing each bit of a 3-bit code word for each memory cell among a group of memory cells operating in parallel, the 3-bit code word being one of eight 3-bit code words generated from a 3-bit code to encode the eight memory states;
• the 3-bit code being constituted from a lower bit, a middle bit and an upper bit, wherein a lower page, middle page and upper page of data are respectively constituted from the lower bit, middle bit and upper bit of each memory cell among the group;
• read circuits for reading page by page, the lower, middle or upper pages each being read by reference to a respective set of read points of predetermined threshold values;
• programming circuits for programming the group of memory cells in parallel, page by page, in order of the lower page, the middle page and then the upper page;
• and
• wherein the respective set of read points for each of the lower, middle or upper pages is invariant irrespective of whether a higher order page has been programmed or not.

A method of operating a non-volatile memory, comprising:

• providing a two-dimensional or three dimensional array of memory cells;
• partitioning a threshold window of each of the individual memory cells into one of eight memory states, the eight memory states being an erase state and seven programmed states;
• encoding the eight memory states with eight 3-bit code words with a predefined ordering;
• each 3-bit code word having a lower bit, a middle bit and an upper bit, and wherein a group of memory cells has a lower page, middle page and upper page of data are respectively constituted from the lower bit, middle bit and upper bit of each memory cell among the group;
• programming the group of memory cells in parallel, page by page, in order of the lower page, the middle page and then the upper page, said programming for each page increasing the threshold value of the group of memory cells in such a way that the respective set of read points for each of the lower, middle or upper pages is invariant irrespective of whether a higher order page has been programmed or not;
• and
• reading page by page, the lower, middle or upper pages, each being read by reference to a respective set of read points of predefined threshold values.