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Double Error Correction for Low End Memories

IP.com Disclosure Number: IPCOM000047601D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Schomburg, JF: AUTHOR

Abstract

Double error correction (DEC) techniques are added to existing memory cards, which contain "single error correct-double error detect" (ECC (error correction code)) circuitry, by the use of off-card inverters and the routing of recomplemented data back to an all-good address in the memory before performing the second stage of the ECC routine. The double complement-retry (DCR) method of correcting two errors (if at least one of them is a "hard" error) requires that the codeword which has two errors be inverted and re-written in memory, then fetched and inverted again before being processed through the ECC circuitry.

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Double Error Correction for Low End Memories

Double error correction (DEC) techniques are added to existing memory cards, which contain "single error correct-double error detect" (ECC (error correction code)) circuitry, by the use of off-card inverters and the routing of recomplemented data back to an all-good address in the memory before performing the second stage of the ECC routine. The double complement-retry (DCR) method of correcting two errors (if at least one of them is a "hard" error) requires that the codeword which has two errors be inverted and re-written in memory, then fetched and inverted again before being processed through the ECC circuitry. In the case of existing cards, where there is no space to retrofit a set of inverters and no way to provide a path for off-card data to pass through the on-card ECC circuitry without passing through the on-card memory arrays, the DCR method can be used if the following is effected: 1. Both reading and writing are done without using the ECC circuitry. 2. Inverters are placed off-card. 3. In order to pass the new codeword through the ECC circuitry, it is written at some address known to

have no errors, and then read back through the ECC

circuitry. 4. If microcode is used to do DCR, it must be held in

memory known to have no errors. Thus, most of the existing card design can be preserved in the modified application.

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