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Circuitry for Performing Error Correction Calculations on Baseband Encoded Data to Eliminate Error Propagation

IP.com Disclosure Number: IPCOM000051822D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Bliss, WG: AUTHOR

Abstract

The circuitry illustrated in the figure modifies the structural relationship (from conventional) between baseband and error correction coding (ECC) such that error correction encoding is performed on data already baseband encoded and possibly error propagating, and the check field thus calculated is baseband encoded with a non-error propagating code (such as MFM) so that many baseband codes with properties desirable for magnetic recording but possibly suffering from error propagation upon decoding can still be used with advanced error correction codes.

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Circuitry for Performing Error Correction Calculations on Baseband Encoded Data to Eliminate Error Propagation

The circuitry illustrated in the figure modifies the structural relationship (from conventional) between baseband and error correction coding (ECC) such that error correction encoding is performed on data already baseband encoded and possibly error propagating, and the check field thus calculated is baseband encoded with a non-error propagating code (such as MFM) so that many baseband codes with properties desirable for magnetic recording but possibly suffering from error propagation upon decoding can still be used with advanced error correction codes.

The circuitry is shown in the figure in connection with magnetic disk 10 having transducer 12 effective on it.

The encoding portion of the circuitry includes baseband 1 encoder 14, ECC encoder 16, baseband 2 encoder 18, switch 20 and write driver 22 connected with transducer 12. The reading portion of the circuitry includes read driver 24, switch 26, baseband 2 decoder 28, switch 3O, ECC decoder 32 and baseband 1 decoder 34, all connected as shown. Data In line 36 supplies data to encoder 14 and Data Out line 38 provides data from decoder 34. Line 40 supplies digital information to encoder 16 from encoder 14, and line 42 supplies digital information from decoder 32 to decoder 34.

Examples of a baseband code particularly desirable for magnetic recording on disk 12 but possibly suffering from error propagation upon decoding is Franaszek's run-length-limited codes [1,2]. Another example of such a desirable baseband code are the table lookup codes (X of Y) described in many code textbooks. Such baseband codes can exhibit the property of propagating a ""short'' error in the readback encoded data into a longer (or infinite error) in the decoded data. This places a large burden on error correcting codes, especially if multiple bursts must be corrected. Thus, if the normal conventional hierarchy of coding is preserved, many otherwise desirable baseband codes are not feasible.

In writing data on disk 10, switch 20 is in its ""data'' position, and data is supplied to encoder 14 which converts it to the desired baseband code, such as one of Fr...