Patent Document ID: 4723244
Application ID: 06782347

Base Claim:
1. In a communication system wherein information is transmitted in the form of a data word representing the information and a check word for error detection, wherein the data word and the check word each include a plurality of code symbol groups, and wherein symbol groups of a received data word are processed at a node of the communications system to produce symbol groups of a modified data word, an apparatus for producing a modified check word to conform with the modified data word, said apparatus comprising: first means for processing a symbol group of the receiving data word and a symbol group of the modified data word after said modified data word symbol group is produced and for producing a comparison symbol group in response thereto; means for encoding said comparison symbol group to produce an encoded symbol group; second means for processing said encoded symbol group and a symbol group of the received check word after said encoded symbol group is produced, to produce a symbol group of the modified check work.

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Claim 4:
4. The apparatus of claim 1 wherein when the symbols of the data and the check words are binary numbers the first means includes an exclusive OR gate having a first input terminal responsive to each symbol of the received data word symbol group and a second input terminal responsive to each symbol of the modified data word symbol group, wherein each symbol of the comparison symbol group is available at the output terminal thereof, wherein said exclusive OR give performs the exclusive OR function on a bit-by-bit serial basis to produce each symbol of the comparison symbol group at the output terminal thereof.