Storage device and control method of nonvolatile memory

1. A storage device comprising:

a nonvolatile memory including blocks, each of the blocks including pages each constituted by a memory cell group, each memory cell being capable of being set at a first threshold voltage and a second threshold voltage;

a controller configured to copy data stored in a first page in a first block to a second page in a second block; and

an ECC circuit configured to correct an error in data read from the nonvolatile memory,

wherein the controller reads data from a part of the first page by using an upper limit voltage and lower limit voltage for determining a threshold voltage of a memory cell,

performs a direct copy operation in the nonvolatile memory without via the ECC circuit if the number of error cells having threshold voltages higher than the lower limit voltage and lower than or equal to the upper limit voltage is less than or equal to a specified value, and

performs error correction by using the ECC circuit if the number of error cells exceeds the specified value.

2. The device of claim 1 , wherein the controller includes a data buffer configured to store the data read from the first page and counts the number of error cells by using data in the data buffer.

3. The device of claim 1 , wherein the nonvolatile memory includes a data buffer configured to store the data read from the first page and a count circuit configured to count the number of error cells by using data in the data buffer.

4. The device of claim 1 , wherein the nonvolatile memory includes a register configured to store an intra-page address corresponding to the part of the first page.

5. The device of claim 1 , wherein the nonvolatile memory includes a register configured to store the upper limit voltage and the lower limit voltage.

6. The device of claim 1 , wherein the nonvolatile memory includes a register configured to store the specified value.

7. The device of claim 1 , wherein

the lower limit voltage corresponds to an upper limit of a distribution of the first threshold voltage, and

the upper limit voltage corresponds to a lower limit of a distribution of the second threshold voltage.

8. The device of claim 1 , wherein

the ECC circuit generates an error correction code for each predetermined data size,

page data includes ECC frames each constituted by the predetermined data size and the error correction code, and

an intra-page address corresponding to the part of the first page is capable of being set regardless of the ECC frame.

9. The device of claim 1 , wherein the upper limit voltage and the lower limit voltage are capable of being changed for each page copy operation.

10. A control method of a nonvolatile memory which includes blocks, each of the blocks including pages each constituted by a memory cell group, and each memory cell being capable of being set at a first threshold voltage and a second threshold voltage,

the control method comprising:

copying data stored in a first page in a first block to a second page in a second block;

reading data from a part of the first page by using an upper limit voltage and lower limit voltage for determining a threshold voltage of a memory cell;

performing a direct copy operation in the nonvolatile memory without via an ECC circuit if the number of error cells having threshold voltages higher than the lower limit voltage and lower than or equal to the upper limit voltage is less than or equal to a specified value; and

performing error correction by using the ECC circuit if the number of error cells exceeds the specified value.

11. The method of claim 10 , further comprising:

storing the data read from the first page in a data buffer; and

counting the number of error cells by using data in the data buffer.

12. The method of claim 10 , further comprising storing an intra-page address corresponding to the part of the first page in a register.

13. The method of claim 10 , further comprising storing the upper limit voltage and the lower limit voltage in a register.

14. The method of claim 10 , further comprising storing the specified value in a register.

15. The method of claim 10 , wherein

the lower limit voltage corresponds to an upper limit of a distribution of the first threshold voltage, and

the upper limit voltage corresponds to a lower limit of a distribution of the second threshold voltage.

16. The method of claim 10 , further comprising generating an error correction code for each predetermined data size,

wherein page data includes ECC frames each constituted by the predetermined data size and the error correction code, and

an intra-page address corresponding to the part of the first page is capable of being set regardless of the ECC frame.

17. The method of claim 10 , wherein the upper limit voltage and the lower limit voltage are capable of being changed for each page copy operation.