Abstract: A method for finding an optimum read voltage includes acquiring difference values between state bit counts of different positions. A direction for finding the optimum read voltage is determined based on the difference values. An offset for finding the optimum read voltage is determined based on correspondence between a difference value of bit count and offset. Reading is performed with the offset applied to a current read reference voltage, wherein upon read-success, the current reference voltage superimposed with the offset is the optimum read voltage, and upon read-error, new first and second positions are obtained based on the direction and the offset for finding the optimum read voltage until reading becomes successful.

Abstract: A method for finding an optimum read voltage includes acquiring difference values between state bit counts of different positions. A direction for finding the optimum read voltage is determined based on the difference values. An offset for finding the optimum read voltage is determined based on correspondence between a difference value of bit count and offset. Reading is performed with the offset applied to a current read reference voltage, wherein upon read-success, the current reference voltage superimposed with the offset is the optimum read voltage, and upon read-error, new first and second positions are obtained based on the direction and the offset for finding the optimum read voltage until reading becomes successful.