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DC-free line code and bit and frame synchronization for arbitrary data transmission

  • US 5,438,621 A
  • Filed: 05/05/1992
  • Issued: 08/01/1995
  • Est. Priority Date: 11/02/1988
  • Status: Expired due to Term
First Claim
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1. A method of encoding a digital bit stream for transmission over a communication link, the method comprising:

  • maintaining a cumulative polarity indicative of bits which have been transmitted over the link during a predefined time interval, the cumulative polarity being positive if more logical one bits than logical zero bits have been transmitted and negative if fewer logical one bits than logical zero bits have been transmitted;

    obtaining a plurality of data bits from the stream for transmission as a data word;

    forming a frame by combining the data bits of the data word with a plurality of additional bits, a predetermined first selected bit of the additional bits having a logical value opposite a second selected bit adjacent to the first selected bit such that the first selected bit and the second selected bit establish a master transition in a predetermined location in the frame;

    selecting a third bit immediately preceding the first selected bit, and selecting a fourth bit immediately following the second selected bit;

    setting the third selected bit to the same logical value as the first selected bit in various ones of a plurality of frames, and setting the fourth selected bit to the same logical value as the second selected bit in various ones of a plurality of flames such that the master transition is not always immediately preceded or immediately followed by another transition; and

    setting the logical values of the combined bits such that the frame has a different polarity than the cumulative polarity, the frame polarity being positive if the frame contains more logical one bits than logical zero bits and negative if the frame contains fewer logical one bits than logical zero bits.

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