Method and apparatus for DC-level constrained coding

A method that constrains a DC level of an input word for a perpendicular recorder that records symbols on a magnetic media, comprising:

• dividing said input word into a plurality of components, wherein said components include n symbols;
• summing said n symbols of said components and generating a sum for each component;
• comparing an absolute value of said sum to a threshold;
• encoding said component into a substitute component having fewer than n symbols if said absolute value of said sum for said component exceeds said threshold;
• combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word, wherein said substitute components reduce a digital sum of said symbols of said input word;
• and
• writing said output word using said perpendicular recorder on said magnetic media.

A DC-level constraining circuit that constrains a DC level of an input word, comprising:

• dividing means for dividing said input word into a plurality of components, wherein said components include n symbols;
• summing means for summing said n symbols of said components and for generating a sum for each component;
• comparing means for comparing an absolute value of said sum to a threshold;
• encoding means for encoding said component into a substitute component if said absolute value of said sum for said component exceeds said threshold;
• and
• combining means for combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word.

A DC-level constraining circuit that constrains a DC level of an input word for a perpendicular recorder that records symbols on a magnetic media, comprising:

• dividing means for dividing said input word into a plurality of components, wherein said components include n symbols;
• summing means for summing said n symbols of said components and for generating a sum for each component;
• comparing means for comparing an absolute value of said sum to a threshold;
• encoding means for encoding said component into a substitute component having fewer than n symbols if said absolute value of said sum for said component exceeds said threshold;
• combining means for combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word, wherein said substitute components reduce a digital sum of said symbols of said input word;
• and
• writing said output word using said perpendicular recorder on said magnetic media.

A DC-level constraining circuit that constrains a DC level of an input word, comprising:

• a divider that divides said input word into a plurality of components, wherein said components include n symbols;
• a summer that sums said n symbols of said components and generates a sum for each component;
• a comparator that compares an absolute value of said sum to a threshold;
• and
• an encoder that encodes said component into a substitute component if said absolute value of said sum for said component exceeds said threshold and combines said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word.

A DC-level constraining circuit that constrains a DC level of an input word for a perpendicular recorder that records symbols on a magnetic media, comprising:

• a divider that divides said input word into a plurality of components, wherein said components include n symbols;
• a summer that sums said n symbols of said components and generates a sum for each component;
• a comparator that compares an absolute value of said sum to a threshold;
• an encoder that encodes said component into a substitute component having fewer than n symbols if said absolute value of said sum for said component exceeds said threshold and that combines said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word, wherein said substitute components reduce a digital sum of said symbols of said input word;
• and
• a perpendicular recorder that writes said output word on said magnetic media.

A method for decoding an output word of DC-level constraining encoder, comprising:

• identifying address and indicator symbols in said output word;
• selecting an output word template based on said address and indicator symbols;
• and
• using said output word template to identify good components and substitute components in said output word.

A DC-level constraining circuit that constrains a DC level of an input word, comprising:

• an error correction coding (ECC) circuit;
• an encoder that communicates with said ECC circuit, wherein said encoder divides said input word into a plurality of components each having n symbols, sums said n symbols of said components and generates a sum for each component, compares an absolute value of said sum to a threshold, encodes said component into a substitute component if said absolute value of said sum for said component exceeds said threshold, and combines said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word;
• and
• a disk drive that communicates with said encoder and that writes said output word onto a magnetic media.

A DC-level constraining circuit that constrains a DC level of an input word, comprising:

• error means for providing error correction coding;
• encoding means that communicates with said error means for dividing said input word into a plurality of components each having n symbols, for summing said n symbols of said components, for generating a sum for each component, for comparing an absolute value of said sum to a threshold, for encoding said component into a substitute component if said absolute value of said sum for said component exceeds said threshold, and for combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word;
• and
• drive means that communicates with said encoding means for writing said output word onto a magnetic media.

A method for constraining a DC level of an input word, comprising:

• error correction coding an input word;
• dividing said input word into a plurality of components each having n symbols;
• summing said n symbols of said components and generating a sum for each component;
• comparing an absolute value of said sum to a threshold;
• encoding said component into a substitute component if said absolute value of said sum for said component exceeds said threshold;
• combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word;
• and
• writing said output word onto a magnetic media.

A DC-level constraining circuit that constrains a DC level of an input word, comprising:

• an error correction coding (ECC) circuit;
• an encoder that communicates with said ECC circuit, wherein said encoder divides said input word into a plurality of components each having n symbols, sums said n symbols of said components and generates a sum for each component, compares an absolute value of said sum to a threshold, encodes said component into a substitute component if said absolute value of said sum for said component exceeds said threshold, and combines said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word;
• and
• an output channel in communication with said encoder.

A DC-level constraining circuit that constrains a DC level of an input word, comprising:

• error means for providing error correction coding;
• encoding means that communicates with said error means for dividing said input word into a plurality of components each having n symbols, for summing said n symbols of said components, for generating a sum for each component, for comparing an absolute value of said sum to a threshold, for encoding said component into a substitute component if said absolute value of said sum for said component exceeds said threshold, and for combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word;
• and
• an output channel in communication with said encoder.

A method for constraining a DC level of an input word, comprising:

• error correction coding an input word;
• dividing said input word into a plurality of components each having n symbols;
• summing said n symbols of said components and generating a sum for each component;
• comparing an absolute value of said sum to a threshold;
• encoding said component into a substitute component if said absolute value of said sum for said component exceeds said threshold;
• combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word;
• and
• transmitting said output word on an output channel.

A decoding circuit for an encoded input word, comprising:

• a preamplifier that communicates with a channel that carries an encoded output word;
• a front end that communicates with said preamplifier;
• a Viterbi coder that communicates with said front end;
• a post processor that communicates with said Viterbi coder;
• and
• a decoder that identifies address and indicator symbols in said output word, that selects an output word template based on said address and indicator symbols, and that uses said output word template to identify good components and substitute components in said encoded output word.

A decoding circuit for an encoded input word, comprising:

• amplifying means that communicates with a channel that carries an encoded output word for amplifying said encoded output word;
• front end means that communicates with said amplifying means and that processes said amplified and encoded output word;
• coding means that communicates with said front end means for applying Viterbi coding;
• processing means that communicates with said coding means for providing post processing;
• and
• decoding means that communicates with said post processing means for identifying address and indicator symbols in said output word, for selecting an output word template based on said address and indicator symbols, and for using said output word template to identify good components and substitute components in said encoded output word.

A method for decoding an encoded input word, comprising:

• communicating with a channel that carries an encoded output word;
• amplifying said encoded output word;
• processing said amplified and encoded output word using a front end;
• coding said amplified and encoded output word using Viterbi coding;
• performing post processing;
• identifying address and indicator symbols in said output word;
• selecting an output word template based on said address and indicator symbols;
• and
• using said output word template to identify good components and substitute components in said encoded output word.

A software method that constrains a DC level of an input word, comprising:

• dividing said input word into a plurality of components, wherein said components include n symbols;
• summing said n symbols of said components and generating a sum for each component;
• comparing an absolute value of said sum to a threshold;
• encoding said component into a substitute component if said absolute value of said sum for said component exceeds said threshold;
• and
• combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word.

A software method that constrains a DC level of an input word for a perpendicular recorder that records symbols on a magnetic media, comprising:

• dividing said input word into a plurality of components, wherein said components include n symbols;
• summing said n symbols of said components and generating a sum for each component;
• comparing an absolute value of said sum to a threshold;
• encoding said component into a substitute component having fewer than n symbols if said absolute value of said sum for said component exceeds said threshold;
• combining said components having said sum with said absolute value that does not exceed said threshold with at least one substitute component into an output word, wherein said substitute components reduce a digital sum of said symbols of said input word;
• and
• writing said output word to an output media.