Patent ID: 8279676
Filing Date: 2012-10-02
Classification: G11C

Abstract:
1. A method of operating a nonvolatile memory device comprising a main cell for storing data including a least significant bit (LSB) and a most significant bit (MSB) and a flag cell for determining a program state of the main cell, the method comprising: reading data stored in the main cell and the flag cell of a nonvolatile memory device using a first read voltage in response to a read command; determining a program state of the main cell based on the data read from the flag cell; reading data stored in the main cell and the flag cell using a second read voltage, in a case in which a most significant bit (MSB) page program has been performed on the main cell; and reading data stored in the main cell using a third read voltage or a fourth read voltage based on the data read from the flag cell using the second read voltage, and outputting the data read from the main cell using the third read voltage or the fourth read voltage, if the data read from the flag cell using the second read voltage indicates a shift in a threshold voltage of the main cell.