A memory that stores a plurality of data storage words, each data storage
word includes a plurality of data storage cells arranged as a plurality of
columns of data storage cells, at least one of the data storage cells
storing data specifying a data value having 3 or more states. The memory
includes a plurality of data lines, one such data line corresponding to
each column of data storage cells. Each data storage cell sets its state
or provides a signal representative of its state via the data line
connected to that cell in response to control signals. The memory also
includes an error encryption circuit for receiving a data word to be
stored in the memory and generating therefrom an encrypted data storage
word. The encryption circuit divides the encrypted data storage word into
a plurality of sub-data storage words. The two least significant bits of
the sub-data storage words are encrypted via a first error-encryption
algorithm and the most significant bits of the sub-data storage words are
either not encrypted or encrypted via a second error encryption algorithm,
the second error encryption algorithm having a Hamming Distance that is
less than the Hamming Distance of the first error-encryption algorithm. An
error decrypting circuit generates a corrected data word from the
uncorrected sub-data storage words by generating an increment or decrement
to be added to an uncorrected sub-data storage word to arrive at a correct
sub-data storage word value.
