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A Sixteen Input, Eight Output XOR Stage for Syndrome Generation

IP.com Disclosure Number: IPCOM000122314D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 57K

Publishing Venue

IBM

Related People

Wade, WD: AUTHOR

Abstract

A class of single error correction, double error detection (SEC-DED) codes is described which enables wiring and circuitry to be minimized. For instance, a total number of 111 gates, which may be 4 or 3 input exclusive ORs (XORs), using 423 inputs are needed to generate the syndrome for a 128 data bit, 9 check bit SEC-DED (137, 128) code.

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This is the abbreviated version, containing approximately 64% of the total text.

A Sixteen Input, Eight Output XOR Stage for Syndrome Generation

      A class of single error correction, double error detection
(SEC-DED) codes is described which enables wiring and circuitry to be
minimized.  For instance, a total number of 111 gates, which may be 4
or 3 input exclusive ORs (XORs), using 423 inputs are needed to
generate the syndrome for a 128 data bit, 9 check bit SEC-DED (137,
128) code.

      The key feature of this class of codes is the 9 x 16 parity
check matrix (PCM) with a balanced number of XOR sums for the first
seven rows and all zeroes in the last two rows.  The PCM is
constructed from one 1-weight, ten 3-weight, and five 5-weight cyclic
vectors.  These 16 cyclic vectors are rotated nine times to generate
the full code. The one 3-weight vector, which has a 3x frequency,
must be removed after two or three rotations.  The modular structure
of each rotation permits the 16 inputs to be fully XORed by only 8
gates whose output is then inputted to a second stage of gates.

      Examination of all combinations of the possible one 1-weight,
ten 3-weight, and fourteen 5-weight cyclic vectors for a nine bit
syndrome code has located only four 9 x 16 PCMs which satisfy the
conditions stated above.  These four PCMs are given in the table.
PCM b can be obtained by reflection and rotation of PCM a and the
reverse.  The same is true of PCMs c and d.

      PCM a             PCM b             PCM c PCM d
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