Memory device to detect and compensate for defective memory cells

A memory device in which a plurality of data are successively written, comprising:

• data holding means for holding data;
• data writing means for writing data into said data holding means;
• data reading means for reading data out of said data holding means;
• write-data holding means for temporarily holding data to be written into said data holding means;
• detecting means for detecting a defective area within said data holding means by detecting a discrepancy between the data obtained by the operation of said data reading means and the data initially written by said data writing means;
• alternate data-holding means having a function equivalent to that of said data holding means;
• alternate data-writing means for writing data into said alternate data-holding means;
• alternate data-reading means for reading data out of said alternate data-holding means;
• switching means for switching the destination of a write operation either to said data holding means or to said alternate data-holding means;
• and
• control means for performing control so that in the first-half period of a successive write operation, the data to be written is stored into said write-data holding means, and said data reading means performs a data read operation immediately after a data write operation by said data writing means, thereby detecting a defective area within said data holding means, and so that in the second-half period of the successive write operation, the destination of the write operation is switched either to said data holding means or to said alternate data-holding means, and the data held in said write-data holding means is written together with the data to be written.

A memory device in which a plurality of data are successively written, comprising:

• first holding means for holding data;
• first writing means for writing data into said first holding means;
• first reading means for reading data out of said first holding means;
• write-data holding means for temporarily holding data to be written into said first holding means during the first-half period of a successive write operation;
• determining means for determining whether or not there is a defective area within said first holding means during the first-half period of the successive write operation by checking whether the data read out of said first holding means agrees with initially written data;
• second holding means for holding data;
• second writing means for writing data into said second holding means;
• second reading means for reading data out of said second holding means;
• and
• switching means for switching the destination of the write operation from said first holding means to said second holding means during the second-half period of the successive write operation when said detecting means has determined that said first holding means contains a defective area.

A memory device in which a plurality of data are successively written, comprising:

• first holding means for holding data;
• second holding means having a function equivalent to that of said first holding means;
• writing means for writing data into said first and said second holding means;
• reading means for reading data out of said first and said second holding means;
• write-data holding means for temporarily holding data to be written into said first holding means during the first-half period of a successive write operation;
• detecting means for detecting a defective area within said first, holding means during the first-half period of the successive write operation by detecting a discrepancy between the data obtained by the operation of said reading means and the data initially written by said writing means;
• and
• switching means for switching the destination of the write operation from said first holding means to said second holding means during the second-half of the successive write operation when said detecting means has detected a defective area within said first holding means.