Method of detecting and correcting errors in digital data storage systems
First Claim
1. Method of detecting errors in digital data, said data being stored as an array of bits, said array having orthogonal extension in at least two dimensions, wherein the improvement comprises generating first parity-dependent check bits in each of said dimensions during the writing of said data into said array;
- regenerating comparable second check bits in each of said dimensions during the reading of said data from said array;
comparing said first and second check bits in at least one of said dimensions to generate an error syndrome;
inverting bits identified as in error by said syndrome; and
comparing said first and second check bits in the remaining of said dimensions, thus determining whether said inverting eliminated errors from said array.
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Abstract
An error detection and correction method for digital data storage is described which comprises horizontal and vertical generation of parity check bits. These may be used to correct errors in up to two bits per word and to indicate whether all errors in a given record have been corrected during a read operation or not. Hamming codes are used to generate check bits in a vertical direction, while cyclic redundancy codes are used in the horizontal direction. The invention is described as embodied in a solid-state memory unit utilizing charge-coupled devices for data storage.
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Citations
24 Claims
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1. Method of detecting errors in digital data, said data being stored as an array of bits, said array having orthogonal extension in at least two dimensions, wherein the improvement comprises generating first parity-dependent check bits in each of said dimensions during the writing of said data into said array;
- regenerating comparable second check bits in each of said dimensions during the reading of said data from said array;
comparing said first and second check bits in at least one of said dimensions to generate an error syndrome;
inverting bits identified as in error by said syndrome; and
comparing said first and second check bits in the remaining of said dimensions, thus determining whether said inverting eliminated errors from said array. - View Dependent Claims (2, 3, 4, 5)
- regenerating comparable second check bits in each of said dimensions during the reading of said data from said array;
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6. Method for detecting and correcting errors in stored digital data, said data being organized into records each comprising at least one word, each word consisting of information bits and stored check bits, comprising the steps of:
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generating check bits corresponding to each word; comparing said generated check bits with said stored check bits; if a single-bit error is indicated by said comparison, inverting a bit indicated as in error and storing the location of said bit in a data register; if a double-bit error is indicated by said comparison, inverting the bit stored at the location defined by the contents of said data register, and inverting a second bit indicated as in error; performing a cyclic redundancy check; and providing an indication of reading accuracy based on the results of said check. - View Dependent Claims (7, 8, 9, 10, 11)
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12. Method of storage of digital data, said data being organized into at least one record comprising at least one word, comprising a read stage and a write stage, the write stage including the following steps:
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generating a first plurality of check bits uniquely corresponding to each word of data; and storing said first plurality of check bits in conjunction with said word; said read stage including the following steps; generating a second plurality of check bits uniquely corresponding to each word of data; comparing said first and second pluralities of check bits to generate an error syndrome; if said syndrome is zero, proceeding with said read operation; if said syndrome is odd, using it to identify a single bit of said word which is in error, inverting said bit, and proceeding with said read operation; if said syndrome is even, comparing it with the contents of a mask register to generate a second error syndrome, using said syndromes to identify two bits in error and inverting said bits; and
, when the last word of said record has been read, providing a representation of whether or not said read operation has been performed without errors. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification