Electrically erasable and programmable memory that allows data update without prior erasure of the memory

Abstract

A processor-implemented method is described for updating a datum stored in a nonvolatile memory, bits of which cannot be overwritten from a first logical state to a second logical state without a prior erasure. A first storage location in the memory that stores a first version of the datum is accessed. A status field of the first storage location is checked to determine whether the first version of the datum has been superseded. If the status field of the first storage location indicates that the first version of the datum has not been superseded, then a most recent version of the datum is stored in a second storage location of the memory. An address of the second storage location is then written into a next location address field of the first storage location and the status field of the first storage location is written to indicate that the first version of the datum has been superseded such that the datum is updated without the prior erasure of the memory. If the status field of the first storage location indicates that the first version of the datum has been superseded, then the next location address field of the first storage location is accessed to obtain the address of a next storage location that stores a second version of the datum that supersedes the first version of the datum. The next storage location is then caused to be the first storage location and the method repeats itself to access the first storage location. An apparatus for storing a datum is also described.