Chip protection register lock circuit in a flash memory device
A chip protection register lock circuit uses a plurality of lock bits in a lock bit register. If the register contains N bits, N/2 bits of the register are coupled to an erase circuit and the remaining N/2 bits are coupled to a programming circuit. After the chip protection register is programmed, the group of N/2 bits coupled to the erase circuit are erased and the remaining N/2 bits are programmed such that an alternating pattern of logical ones and zeros are in the lock bit register. A read and compare circuit generates a lock indication if the alternating pattern is present.
1. A non-volatile memory device comprising:
a memory array comprising a plurality of non-volatile memory cells;
an N-bit mini array comprising non-volatile memory cells that is separate from the memory array; and
means for generating a lock indication comprising:
means for programming a first group comprising a first predetermined quantity of bits of the N-bit mini array;
means for erasing a second group comprising a second predetermined quantity of bits of the N-bit mini array; and
means for comparing bits within each of the first and second groups for generating the lock indication when the mini array contains a predetermined lock pattern.
2. The device of claim 1 wherein the means for comparing comprises a NOR function coupled to the first group and an input AND function coupled to the second group.
3. The device of claim 2 wherein the means for comparing further comprises an output AND function coupled to the NOR and the input AND such that a logical one is generated when the mini array contains the predetermined lock pattern.
4. The device of claim 1 wherein the first group is comprised of N/2 bits of the N-bit mini array and the second group is comprised of the remaining N/2 bits of the N-bit mini-array.
5. The device of claim 1 wherein N=8 and the predetermined lock pattern is 10101010.
6. The device of claim 1 wherein the non-volatile memory device is a NAND flash memory device.
7. The device of claim 1 wherein the non-volatile memory device is a NOR flash memory device.
8. A method for generating a lock indication in a memory device, the memory device having a non-volatile memory array and a non-volatile mini array that is separate from the memory array and comprising N bits, the method comprising:
performing an erase operation on a first group of the N bits;
performing a programming operation on a second group of the N bits;
comparing each of the first group and the second group to respective predetermined patterns; and
generating the lock indication in response to the comparison.
9. The method of claim 8 wherein the first group is comprised of N/2 bits of the N-bit non-volatile register.
10. The method of claim 8 wherein the second group is comprised of the remaining N/2 bits of the N-bit non-volatile register.
11. The method of claim 8 wherein the erase operation is performed on even N/2 bits of the lock bit register and the programming operation is performed on odd N/2 bits of the N-bit non-volatile register.
12. The method of claim 8 wherein the first group is compared to a predetermined pattern of all logical ones and the second group is compared to a predetermined pattern of all logical zeros.
13. An electronic system comprising:
a processor that generates control signals; and
a non-volatile memory device, coupled to the processor, for storing data in a non-volatile memory array in response to the control signals, the non-volatile memory device comprising:
a memory array comprising a plurality of memory cells;
a mini array comprising N non-volatile lock bits that is separate from the memory array; and
a lock indication circuit coupled to the mini array, the circuit comprising:
a program circuit coupled to a first group of the N non-volatile lock bits, the first group comprising a first predetermined quantity of the N non-volatile lock bits;
an erase circuit coupled to a second group of the N non-volatile lock bits, the second group comprising a second predetermined quantity of the N non-volatile lock bits; and
a comparison circuit for comparing the first group to a first predetermined pattern, the second group to a second predetermined pattern, and generating a lock indication in response to the comparisons.
14. The system of claim 13 wherein the comparison circuit comprises a NOR function coupled to the first group, an input AND function coupled to the second group, and an output AND function coupled to the NOR and input AND functions such that the lock indication is a logical one in response to the N non-volatile lock bits storing a predetermined lock pattern.