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Implied Retention of Byte Parity Bits when Using Error Correcting Codes

IP.com Disclosure Number: IPCOM000092376D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 87K

Publishing Venue

IBM

Related People

Stanton, RJ: AUTHOR [+2]

Abstract

Excess capacity of a Hamming type error-correction code ecc, when available, can be used to advantage to carry information not related to the error-correction function. With sufficient excess capacity, several bits of such unrelated information can be carried through the ecc channels.

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Implied Retention of Byte Parity Bits when Using Error Correcting Codes

Excess capacity of a Hamming type error-correction code ecc, when available, can be used to advantage to carry information not related to the error- correction function. With sufficient excess capacity, several bits of such unrelated information can be carried through the ecc channels.

For this purpose the excess positions of the detected ecc, that is, the code resulting from a comparison of an original ecc carried as a supplement to a data word and an ecc newly generated from the same word, are treated as virtual or pseudo bits. The unrelated information is considered present in the ecc when and only when the detected ecc is one of the codes assigned to a virtual bit. In the example described, the unrelated information is the validity of segments of the word supplemented by the corresponding virtual ecc.

Shown at A is a system comprising a Memory with internal error correction and a User device such as a computer. The latter has the ability to detect, but not correct, byte errors.

With regard to the use of the virtual codes, words in the User system contain four bytes, each consisting of eight data bits and a parity check bit. Memory words consist of thirty-two data bits supplemented by six ecc bits. In transfers of words from User to Memory, the four byte parity check bits of the User word are normally discarded. A group of six newly generated bits of a Hamming type ecc, suitable for detection and correction of single bit errors, is supplied at the Memory interface. Conversely, in transfers from Memory to User the supplemental ecc is discarded and replaced by four newly generated byte parity error detection bits.

The six ecc bits in the memory system have the capacity as a code to assume 2/6/ =64 distinct combinational states. In this system, one state is used to indicate the error free condition and thirty-eight more of these combinational states are used to identify erroneous bit positions of the associated word. The remaining states, which normally are not used, represent excess capacity of the ecc. As explained below the remaining states can be used to denote errors in virtual positions of a word which correspond to validity information supplied by the User system.

In transfers of words from User to Me...