System and method for write-protecting predetermined portions of a memory array

• US 5,394,367 A
• Filed: 03/18/1994
• Issued: 02/28/1995
• Est. Priority Date: 03/18/1994
• Status: Expired due to Fees

• Current Assignee: Ramtron International Corporation (Infineon Technologies AG)
• Original Assignee: Ramtron International Corporation (Infineon Technologies AG)
• Inventors: Downs, Jeffery E., Yeager, Michael W.
• Primary Examiner(s): Yoo, Do Hyun
• Assistant Examiner(s): Tran, Andrew Q.
• Application Number:
  US08/210,699
• Time in Patent Office: 347 Days
• Field of Search: 365/195, 365/189.07, 365/145, 365/185, 365/189.01, 365/230.01, 342/51
• US Class Current: 365/195
• CPC Class Codes: G11C 7/24 Memory cell safety or protection circuits, e.g. arrangements for preventing inadvertent reading or writing; Status cells; Test cells

Abstract

A system and method wherein a predetermined soft fuse value may be written to a corresponding soft fuse register to control subsequent access to a number of lock bits in a non-volatile semiconductor memory array which are provided for selectively precluding writes to predetermined portions of the memory array. In a specific embodiment, the system and method may be utilized in conjunction with radio frequency ("RF") identification ("ID") transponders incorporating a non-volatile ferroelectric random access memory ("FRAM") array integrated circuit.

Claims

1. A method for write-protecting predetermined portions of a memory array utilizing a number of lock bits settable for controlling subsequent writes to selected ones of said predetermined portions of said memory array, said method comprising the steps of:

defining a first memory location for containing a known value forming a soft fuse value and a second memory location for containing said lock bits;

reading the contents of said first memory location to determine a read-out contents thereof;

comparing said read-out contents of said first memory location to said soft fuse value;

allowing setting and resetting of individual ones of said lock bits if said read-out contents do not correspond to said soft fuse value; and

allowing setting and disallowing resetting of individual ones of said lock bits if said read-out contents correspond to said soft fuse value.

2. The method of claim 1 wherein said step of defining comprises the step of partitioning said first and second memory locations within said memory array.

3. The method of claim 1 wherein said step of defining comprises the step of providing an additional memory word of said memory array as said first memory location.

4. The method of claim 1 wherein said step of defining is carried out by means of a non-volatile storage device.

5. The method of claim 4 wherein said non-volatile storage device comprises a ferroelectric random access memory integrated circuit.

6. The method of claim 1 further comprising the step of:

writing said soft fuse value to said first memory location prior to said step of reading.

7. The method of claim 1 further comprising the step of:

indicating to an external device whether said first memory location contains said soft fuse value.

8. An integrated circuit including a memory array having predetermined write-protectable portions thereof utilizing a number of lock bits settable for controlling subsequent writes to selected ones of said write-protectable portions, said memory array comprising:

first and second memory locations for containing a known value forming a soft fuse value and said lock bits respectively;

means, coupled to said first memory location, for comparing;

coupled to said first memory location, for reading the contents of said first memory location to determine a read-out contents thereof;

means, coupled to receive said soft fuse value and said read-out contents, for comparing said read-out contents of said first memory location to said soft fuse value;

means, coupled to said second memory location and responsive to said means for comparing, for allowing setting and resetting of individual ones of said lock bits if said read-out contents do not correspond to said soft fuse value; and

means, coupled to said second memory location and resposive to said means for comparing for allowing setting and disallowing resetting of individual ones of said lock bits if said read-out contents correspond to said soft fuse value.

9. The integrated circuit of claim 8 wherein said memory array comprises a non-volatile memory array.

10. The integrated circuit of claim 9 wherein said memory array comprises a ferroelectric memory array.

11. The integrated circuit of claim 10 wherein said first and second memory locations comprise a portion of said ferroelectric memory array.

12. The integrated circuit of claim 8 further comprising:

means for writing said soft fuse value to said first memory location in response to an external device.

13. The integrated circuit of claim 12 further comprising:

means for indicating to said external device whether said first memory location contains said soft fuse value.

14. An RF transponder including a memory array having predetermined write-protectable portions thereof utilizing a number of lock bits settable for controlling subsequent writes to selected ones of said write-protectable portions, said memory array comprising:

first and second memory locations for containing a known value forming a soft fuse value and said lock bits respectively;

means, coupled to said first memory location, for reading the contents of said first memory location to determine a read-out contents thereof;

means, coupled to receive said soft fuse value and said read-out contents, for comparing said read-out contents of said first memory location to said soft fuse value;

means, coupled to said second memory location and responsive to said means for comparing, for allowing setting and resetting of individual ones of said lock bits if said read-out contents do not correspond to said soft fuse value; and

means, coupled to said second memory location and responsive to said means for comparing, for allowing setting and disallowing resetting of individual ones of said lock bits if said read-out contents correspond to said soft fuse value.

15. The RF transponder of claim 14 wherein said memory array comprises a non-volatile memory array.

16. The RF transponder of claim 15 wherein said memory array comprises a ferroelectric memory array.

17. The RF transponder of claim 16 wherein said first and second memory locations comprise a portion of said ferroelectric memory array.

18. The RF transponder of claim 14 further comprising:

means for writing said soft fuse value to said first memory location in response to an external device.

19. The RF transponder of claim 18 further comprising:

means for indicating to said external device whether said first memory location contains said soft fuse value.

20. The RF transponder of claim 19 wherein said external device is an RF controller.

21. The RF transponder of claim 20 wherein said means for indicating comprises a number of bits transmitted to said RF controller indicative of said soft fuse value being present or not present in said first memory location.