Method for reliably storing non-data fields in a flash EEPROM memory array

• US 5,448,577 A
• Filed: 10/30/1992
• Issued: 09/05/1995
• Est. Priority Date: 10/30/1992
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Wells, Steven E., Hasbun, Robert N.
• Primary Examiner(s): Envall, Jr., Roy N.
• Assistant Examiner(s): NGO, CHUONG D
• Application Number:
  US07/969,464
• Time in Patent Office: 1,040 Days
• Field of Search: 371/10.1, 371/10.2, 371/21.1, 371/21.2, 371/21.3, 371/37.1, 371/40.1, 371/51.1
• US Class Current: 714/767
• CPC Class Codes: G06F 11/1068 in sector programmable memories, e.g. flash disk G06F11/1072 takes precedence
• CPC Class Codes: H03M 13/09 Error detection only, e.g. using cyclic redundancy check [CRC] codes or single parity bit

Abstract

A method for utilizing a cyclical redundancy check value with an identification field stored in memory which is constantly changing between testing of the cyclical redundancy check value. In order to allow the use of a cyclical redundancy check value with a field which constantly varies as does the field in a flash EEPROM memory array, various portions of the field are masked to the cyclical redundancy check and additional reliability checks are utilized to assure that those portions which are masked remain reliable.

Claims

1. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays comprising the steps of:

generating a cyclical redundancy check value for each non-data field written and storing the cyclical redundancy check value with the field as the field is written,

generating a new cyclical redundancy check value each time a non-data field is read,

comparing a cyclical redundancy check value stored with a field with a new cyclical redundancy check value generated when a field is read,

and invalidating a field for which a cyclical redundancy check value stored with a field and a new cyclical redundancy check value generated when a field is read do not compare.

2. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 1 in which data in the field may change between when a field is written and when a field is read in which the step of comparing a cyclical redundancy check value stored with a field with a new cyclical redundancy check value generated when a field is read further comprises the step of masking bits of a field which may change.

3. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 2 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking valid bits of a field.

4. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 2 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking revision bits of a field.

5. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 1 in which the steps of generating a cyclical redundancy check value and a new cyclical redundancy check value each comprise the steps of:

establishing a table of cyclical redundancy check values;

selecting an initial value from the table of cyclical redundancy check values;

performing a logical XOR operation using the initial value and a selected number of bits of a field;

using the result of the logical XOR operation to select a cyclical redundancy check value from the table;

performing a logical XOR operation using the cyclical redundancy check value selected from the table and a next selected number of bits of a field; and

continuing the operation of using the result of the logical XOR operation to select a cyclical redundancy check value from the table, and performing a logical XOR operation using the cyclical redundancy check value selected from the table and a next selected number of bits of a field until all bits of the field have been utilized.

6. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 5 in which each step of performing a logical XOR operation using the cyclical redundancy check value selected from the table and a next selected number of bits of a field includes a step of masking bits of a field which may change.

7. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 6 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking valid bits of a field.

8. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 6 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking revision bits of a field.

9. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 6 in which data in the field may change between when a field is written and when a field is read further including the step of duplicating bits of a field which changes.

10. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 6 in which data in the field may change between when a field is written and when a field is read further including the step of duplicating bits of a field which changes if the change would cause an error in the use of the field.

11. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 5 in which data in the field may change between when a field is written and when a field is read further including, before the step of invalidating a field for which a cyclical redundancy check value stored with a field and a new cyclical redundancy check value generated when a field is read do not compare, a step of repeating the process at a slower speed when a cyclical redundancy check value stored with a field and a new cyclical redundancy check value generated when a field is read do not compare.

12. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 11 in which the step of repeating the process at a slower speed when a cyclical redundancy check value stored with a field and a new cyclical redundancy check value generated when a field is read do not compare comprises setting a microprocessor running the process to include a greater number of wait states in running the process.

13. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays comprising the steps of:

generating an error detection value for each non-data field written and storing the error detection value with the filed as the field is written;

generating a new error detection value each time a non-data field is read,

comparing an error detection value stored with a field with a new error detection value generated when a field is read;

and invalidating a field for which an error detection value stored with a field and a new error detection value generated when a field is read do not compare.

14. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 13 in which data in the field may change between when a field is written and when a field is read in which the step of comparing an error detection value stored with a field with a new error detection value generated when a field is read further comprises the step of masking bits of a field which may change.

15. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 14 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking valid bits of a field.

16. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 14 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking revision bits of a field.

17. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 13 in which the steps of generating an error detection value and a new error detection value each comprise the steps of:

established a table of error detection values;

selecting an initial value from the table of error detection values;

performing a logical XOR operation using the initial value and a selected number of bits of a field;

using the result of the logical XOR operation to select an error detection value from the table;

performing a logical XOR operation using the error detection value selected from the table and a next selected number of bits of a field; and

continuing the operation of using the result of the logical XOR operation to select an error detection value from the table, and performing a logical XOR operation using the error detection value selected from the table and a next selected number of bits of a field until all bits of the field have been utilized.

18. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 17 in which each step of performing a logical XOR operation using the error detection value selected from the table and a next selected number of bits of a field includes a step of masking bits of a field which may change.

19. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 18 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking valid bits of a field.

20. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 18 in which data in the field may change between when a field is written and when a field is read in which the step of masking bits of a field which may change comprises masking revision bits of a field.

21. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 18 in which data in the field may change between when a field is written and when a field is read further including the step of duplicating bits of a field which changes.

22. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 18 in which data in the field may change between when a field is written and when a field is read further including the step of duplicating bits of a field which changes if the change would cause an error in the use of the field.

23. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 17 in which data in the field may change between when a field is written and when a field is read further including, before the step of invalidating a field for which an error detection value stored with a field and a new error detection value generated when a field is read do not compare, a step of repeating the process at a slower speed when an error detection value stored with a field and a new error detection value generated when a field is read do not compare.

24. A method for assuring the reliability of non-data fields in flash EEPROM memory arrays as claimed in claim 23 in which the step of repeating the process at a slower speed when an error detection value stored with a field and a new error detection value generated when a field is read do not compare comprises setting a microprocessor running the process to include a greater number of wait states in running the process.