Dual function ECC system with block check byte

In a dual function ECC system for alternately correcting from a single syndrome byte random 1-bit errors in a data word having M-1 data byte positions and one check byte position, or multi-bit errors in the same byte position of successive data words, where corresponding bytes of successive data words are each stored in a failure independent storage unit and where each said syndrome byte is developed from a write check character and a read check character where each bit position of said check characters represents the modulo-2 sum of the value of data in bit positions of a data word which have been selected from a parity check matrix H' derived from a parity check matrix H which corresponds to an m-sequence of length 2.sup.b -1 where b is equal to the number of bit positions in each said byte, said H' matrix being derived by selecting M b.times.b submatrices from said H matrix which are spaced apart .lambda.-b columns, where .lambda. is greater than b and is selected such that none of the selected submatrices overlap, and means for generating said syndrome byte for each word, said system including:

• (a) a syndrome processing circuit having an input and an output and operable to provide at said output a sequence of different b bit vectors, each vector being positionally related in said m-sequence to said syndrome byte by a factor K.lambda. where K is the position number in said sequence;
• (b) means for transferring each non-zero syndrome byte to said processing circuit;
• and
• (c) means responsive to the output of said processing circuit to indicate the byte location and error pattern of a random single-bit error in said data word and for correcting said error, the improvement comprising:
• (1) means for logging the indicated byte location, the single-bit error pattern, and said non-zero syndrome byte for each processed word where a correction was made for a predetermined number of processed words;
• (2) means for generating a write block check character, a read block check character, and a block syndrome byte from said block check characters which is related by a linear function to the sum of all errors which occurred in the data byte positions of said predetermined number of processed words;
• (3) a comparator;
• and
• (4) summing means to provide a summed error pattern byte from all said single-bit error patterns;
• said comparator being operable at the end of each said block of words for comparing said block syndrome byte with said summed error pattern byte to confirm the validity of each said single-bit error pattern correction.