Patent Document ID: 4851837
Application ID: 06865725

Base Claim:
1. A method of processing digital information prior to recording, comprising the steps of: inputting a succession of digital words each comprising a plurality of bit locations; generating a respective code word for each digital word, with each word having the same period as the input digital word but a number of time slots which is twice the number of bit locations in an input digital word, each code word having a minimum spacing of a period equal to the period of three time slots between adjacent transitions; providing a running sum whose value depends on the number and spacing of transitions in successively generated code words; and providing four groups of code words from which each successive code word is generated, the four groups comprising first and second group pairs, the code word generated for a particular digital word being generated from the particular group in a group pair as a function of the polarity of the running sum; defining a predetermined adjacent pair of time slots, being the same time slots for each code word, code words in the first group pair having no transitions in the predetermined time slots, and code words in the second group pair having a transition in one or other of the predetermined time slots; the code word generated for a particular digital word being generated from the first or second group pair in dependence on the immediately preceding code word, and if the code word is to be generated from the second group pair, the position of the transition within the predetermined pair of time slots is dependent on the particular digital word that is being coded.

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Claim 4:
4. A method in accordance with claim 1, wherein the running sum is updated for each successive code word at the same time as the code word is being selected, by monitoring the characteristics of the code word as it is being selected.