Memory device and memory system

1. A memory device comprising:

memory elements which store data and parity;

a first decoder which, when a first operation including checking of the data is performed while no external access is being made to the memory device, uses a syndrome generated from the data and the parity to correct an error of a maximum of a first number of bits in a unit of the data; and

a second decoder which, when reading of the data is performed, uses the syndrome to correct an error of a maximum of a second number of bits in a unit of the data,

wherein the second number of bits is smaller than the first number of bits,

wherein in response to a first command, the memory device:

reads the data and the parity from the memory elements,

generates the syndrome from the data and the parity, and

uses the syndrome to correct the error of the data, and

wherein in response to a read command, the memory device:

reads the data and the parity from the memory elements,

generates the syndrome from the data and the parity,

uses the syndrome to correct the error of the data, and

transmits the data in which the error has been corrected.

2. The memory device according to claim 1 , further comprising:

an encoder which generates the parity from data to be written in the memory elements; and

a syndrome generator which generates the syndrome from the data and the parity,

wherein the parity and the syndrome are generated to allow an error of the first number of bits to be detected.

3. The memory device according to claim 1 , wherein when the first operation is performed, the data in which the error has been corrected is written in the memory elements.

4. The memory device according to claim 1 , wherein during the first operation, an alert is issued when a number of erroneous bits in a unit of the data is larger than the first number of bits.

5. The memory device according to claim 1 , wherein during the first operation, data received externally is re-written when a number of erroneous bits in a unit of the data is larger than the first number of bits.

6. The memory device according to claim 1 , wherein during the reading of the data, an alert is issued when a number of erroneous bits in a unit of the data is larger than the second number of bits.

7. The memory device according to claim 1 , wherein during the reading of the data, the first operation is performed or data received externally is re-written when a number of erroneous bits in a unit of the data is larger than the second number of bits.

8. A memory system comprising:

a memory device including memory elements which store data and parity;

a memory controller which controls the memory device; and

a host device which controls the memory controller,

wherein during a first operation including checking of the data, the memory controller:

transmits a first command to the memory device to read the data and the parity from the memory elements while no external access is being made to the memory device,

generates a syndrome from the data and the parity, and

uses the syndrome to correct an error of a maximum of a first number of bits in a unit of the data,

wherein during reading of the data, the memory controller:

transmits a read command to the memory device, and reads the data and the parity from the memory elements,

generates a syndrome from the data and the parity, and

uses the syndrome to correct an error of a maximum of a second number of bits in a unit of the data, and

wherein the second number of bits is smaller than the first number of bits.

9. The memory system according to claim 8 , wherein the parity and the syndrome are generated to allow an error of the first number of bits to be detected.

10. The memory system according to claim 8 , wherein the memory controller includes:

an encoder which generates the parity,

a syndrome generator which generates the syndrome,

a first decoder which corrects the error of the maximum of the first number of bits in a unit of the data, and

a second decoder which corrects the error of the maximum of the second number of bits in a unit of the data.

11. The memory system according to claim 8 , wherein:

during the first operation, the memory controller transmits the data in which the error has been corrected to the memory device, and

the memory device writes the data in which the error has been corrected to the memory elements.

12. The memory system according to claim 8 , wherein the memory controller issues an alert when a number of erroneous bits in a unit of the data is larger than the first number of bits during the first operation, or when a number of erroneous bits in a unit of the data is larger than the second number of bits during the reading of the data.

13. The memory system according to claim 8 , wherein:

during the first operation, the memory controller retransmits the data for writing together with a write command when a number of erroneous bits in a unit of the data is larger than the first number of bits, and

during the reading of the data, the memory controller transmits the first command to the memory device, or retransmits the data for the writing together with the write command when a number of erroneous bits in a unit of the data is larger than the second number of bits.

14. A memory system comprising:

a memory device including memory elements which store data and parity;

a memory controller which controls the memory device; and

a host device which controls the memory controller,

wherein:

during a first operation, the memory controller transmits a first command to the memory device while no external access is being made to the memory device,

in response to the first command, the memory device reads the data and the parity from the memory elements, generates a syndrome from the data and the parity, and transmits the syndrome to the memory controller,

upon receipt of the syndrome, the memory controller uses the syndrome to correct an error of a maximum of a first number of bits in a unit of the data,

during reading of the data, the memory controller transmits a read command to the memory device,

in response to the read command, the memory device reads the data and the parity from the memory elements, generates a syndrome from the data and the parity, uses the syndrome to correct an error of a maximum of a second number of bits in a unit of the data, and transmits the data in which the error has been corrected to the memory controller, and

wherein the second number of bits is smaller than the first number of bits.

15. The memory system according to claim 14 , wherein the parity and the syndrome are generated to allow an error of the first number of bits to be detected.

16. The memory system according to claim 14 , wherein:

the memory controller includes a first decoder which corrects the error of the maximum of the first number of bits in a unit of the data, and

the memory device includes an encoder which generates the parity, a syndrome generator which generates the syndrome, and a second decoder which corrects the error of the maximum of the second number of bits in a unit of the data.

17. The memory system according to claim 14 , wherein:

during the first operation, the memory controller transmits the data in which the error has been corrected to the memory device, and

the memory device writes the data in which the error has been corrected to the memory elements.

18. The memory system according to claim 14 , wherein:

during the first operation, the memory controller issues an alert when a number of erroneous bits in a unit of the data is larger than the first number of bits, and

during the reading of the data, the memory device issues an alert when a number of erroneous bits in a unit of the data is larger than the second number of bits.

19. The memory system according to claim 14 , wherein:

during the first operation, the memory controller retransmits the data for writing together with a write command when a number of erroneous bits in a unit of the data is larger than the first number of bits, and

during the reading of the data, the memory controller transmits the first command to the memory device, or retransmits the data for the writing together with the write command, when a number of erroneous bits in a unit of the data is larger than the second number of bits.