Method and system to recognize change in the storage characteristics of a programmable memory
First Claim
1. Method to recognize change in the storage characteristics and affecting a stored memory content in a read-only memory (ROM) element, especially an erasable programmable read-only memory element (EPROM) having programmed memory cells,in which a computer (1) is provided, capable of sequentially generating read-out command signals and the memory element or cells thereof are addressable by the computer, comprising the steps ofreading-out a first time the memory content of addressed cells of the read-only memory element with a standard or design read-out voltage;
- storing the memory content of the cells of the read-only memory element, as read out the first time, in a computer memory;
reading-out a second time the memory content of said previously addressed cells of the read-only memory with a read-out voltage which differs from said standard or design read-out voltage;
comparing the content stored in the computer memory, as read out the first time, with the data derived from the cells of the memory element as read-out said second time;
and generating an error signal upon non-concurrence of the data derived from the read-only memory element as read out the second time with the content of the computer memory.
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Accused Products
Abstract
To recognize change in the storage characteristics of programmable memory elements, particularly EPROMs, the memory content of an addressed memory element or cell is read out, the first time, at normal design voltage level; the data so read are then again read out at a changed voltage level, for example at a higher or lower read-out voltage, or higher or lower operating voltage of the EPROM, and compared. If the data do not match, the particular memory cell will have the tendency to become defective due to loss or accumulation of charge carriers in due course although, for some time yet, the specific memory cell will function satisfactorily. Detection of errors upon operation under changed voltage conditions provides early warning of failure of a cell.
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Citations
14 Claims
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1. Method to recognize change in the storage characteristics and affecting a stored memory content in a read-only memory (ROM) element, especially an erasable programmable read-only memory element (EPROM) having programmed memory cells,
in which a computer (1) is provided, capable of sequentially generating read-out command signals and the memory element or cells thereof are addressable by the computer, comprising the steps of reading-out a first time the memory content of addressed cells of the read-only memory element with a standard or design read-out voltage; -
storing the memory content of the cells of the read-only memory element, as read out the first time, in a computer memory; reading-out a second time the memory content of said previously addressed cells of the read-only memory with a read-out voltage which differs from said standard or design read-out voltage; comparing the content stored in the computer memory, as read out the first time, with the data derived from the cells of the memory element as read-out said second time; and generating an error signal upon non-concurrence of the data derived from the read-only memory element as read out the second time with the content of the computer memory. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. In combination with a read-only memory (ROM), especially an erasable programmable read-only memory (EPROM),
an incipient error recognition sytem to recognize change in the storage characteristics of memory cells in the read-only memory (ROM) element (4) having a voltage applying means to apply operating voltage to the memory element; -
a computer (1) capable of sequentially generating read-out or interrogating signals, connected to said read-only memory element, and addressing selected addressable cells in the read-only memory, said computer having a computer having a computer memory, comprising means (8-13) coupled to the read-only memory for controlling an operating voltage applied to the read-only memory by the voltage applying means between at least two selected voltage levels, in which one of the voltage levels is at a standard or design level, and another voltage level is changed with respect to said standard or design level in increasing or decreasing direction; and means (5) coupled to the voltage applying means connected to and controlled by the computer (1) for reading-out the memory of said read-only memory at (a) the standard or design voltage; and
, also(b) at another voltage level; the computer memory being connected for storing the content of the read-only memory during read-out of the content at said standard or design level; said computer further including a comparator, the comparator being connected to and controlled by said selective voltage applying means (5) and connected to compare the stored memory content in the computer memory with the content of the read-only memory (ROM) being read out at said other voltage level, wherein said computer (1) provides sequentially generated read-out command signals, and the memory element, or cells thereof are addressable by the computer; said computer controlling reading-out a first time the memory content of addressed cells of the read-only memory element with a standard or design read-out voltage; storing the memory content of the cells of the read-only memory element, as read out the first time, in a computer memory; reading-out a second time the memory content of said previously addressed cells of the read-only memory with a read-out voltage which differes from said standard or design read-out voltage; comparing the content stored in the computer memory, as read out the first time, with the data derived from the cells of the memory element as read-out said second time; and generating an error signal upon non-concurrence of the data derived from the read-only memory element as read out the second time with the content of the computer memory. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification