Semiconductor memory having control means for preventing unauthorized erasure of a memory array portion
First Claim
1. A single-chip microcomputer having a non-volatile memory and a central processing unit coupled to the non-volatile memory and to a random access memory, the non-volatile memory comprising:
- a memory array comprising a first group of non-volatile memory cells and a second group of non-volatile memory cells;
electrical erasure means for executing an erasure operation on said memory array;
selecting means, coupled to said memory array, for selecting a non-volatile memory cell from said memory array;
designating means, coupled to the electrical erasure means, for designating whether the selected non-volatile memory cell is in the first group of non-volatile memory cells or in the second group of non-volatile memory cells;
control register means, coupled to the electrical erasure means, for controlling the erasure operation of the electrical erasure means on said memory array including a first control bit means, the firsts control bit means having a first state for inhibiting the eraser operation of the electrical erasure means on the memory array and a second state for enabling the erasure operation of the electrical erasure means on the memory array; and
,erase inhibit override means for inhibiting the erasure operation of the electrical erasure means on the second group of non-volatile memory cells regardless of the second state of the first control bit means when the designating means designates that the selected non-volatile memory cell is in the second group of non-volatile memory cells.
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Accused Products
Abstract
A volatile storage circuit for latching data is disposed outside a non-volatile memory array. Before a bulk erase of the memory array, some of the data items contained therein are transferred to and held by the storage circuit. The data items thus saved are rewritten to the non-volatile memory array after the bulk erase, or alternatively, on the basis of control data items transferred to the storage circuit, only regions designated by these data items are subjected to the bulk erase. Thus, in case of a bulk erase of an EEPROM, some of the stored data items can be preserved, so as to prevent illicit use of and maintain the integrity of the preserved data. Also the testing time of the data rewritten to the memory array is reduced because of the elimination of the need to test the memory area containing the preserved data in that only the integrity of the memory area containing data sourced externally need be tested.
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Citations
14 Claims
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1. A single-chip microcomputer having a non-volatile memory and a central processing unit coupled to the non-volatile memory and to a random access memory, the non-volatile memory comprising:
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a memory array comprising a first group of non-volatile memory cells and a second group of non-volatile memory cells; electrical erasure means for executing an erasure operation on said memory array; selecting means, coupled to said memory array, for selecting a non-volatile memory cell from said memory array; designating means, coupled to the electrical erasure means, for designating whether the selected non-volatile memory cell is in the first group of non-volatile memory cells or in the second group of non-volatile memory cells; control register means, coupled to the electrical erasure means, for controlling the erasure operation of the electrical erasure means on said memory array including a first control bit means, the firsts control bit means having a first state for inhibiting the eraser operation of the electrical erasure means on the memory array and a second state for enabling the erasure operation of the electrical erasure means on the memory array; and
,erase inhibit override means for inhibiting the erasure operation of the electrical erasure means on the second group of non-volatile memory cells regardless of the second state of the first control bit means when the designating means designates that the selected non-volatile memory cell is in the second group of non-volatile memory cells. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An integrated circuit card comprising a single-chip microcomputer having a non-volatile memory and a central processing unit coupled to the non-volatile memory and to a random access memory, the non-volatile memory comprising:
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a memory array comprising a first group of non-volatile memory cells and a second group of non-volatile memory cells; electrical erasure means for executing an erasure operation on said memory array; selecting means, coupled to said memory array, for selecting a non-volatile memory cell from said memory array; designating means, coupled to the electrical erasure means, for designating whether the selected non-volatile memory cell is in the first group of non-volatile memory cells or in the second group of non-volatile memory cells; control register means, coupled to the electrical erasure means, for controlling the erasure operation of the electrical erasure means on said memory array including a first control bit means, the firsts control bit means having a first state for inhibiting the eraser operation of the electrical erasure means on the memory array and a second state for enabling the erasure operation of the electrical erasure means on the memory array; and
,erase inhibit override means for inhibiting the erasure operation of the electrical erasure means on the second group of non-volatile memory cells regardless of the second state of the first control bit means when the designating means designates that the selected non-volatile memory cell is in the second group of non-volatile memory cells. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification