DC-free line code and bit and frame synchronization for arbitrary data transmission
First Claim
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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Accused Products
Abstract
A method of encoding data for transmission over a communication link. A cumulative polarity of previously-transmitted frames is maintained. A frame is prepared for transmission by combining a data word with a plurality of additional bits. The additional bits provide a master transition. A phantom bit is encoded in the additional bits. If the polarity of the frame is the same as the cumulative polarity, the data bits or in some instances all the bits are inverted so as to maintain balance. Control words and fill words are provided and are distinguished from data words by encoding the additional bits. Control words carry additional data or control instructions and are distinguished from fill words by the number of transitions. The phantom bit either conveys additional data or is used for such purposes as error checking.
71 Citations
23 Claims
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1. A method of encoding a digital bit stream for transmission over a communication link, the method comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of encoding a digital bit stream for transmission over a communication link, the method comprising:
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maintaining a cumulative polarity indicative of bits which have been transmitted over the link during a predefined 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; selecting a word from among a plurality of data bits from the stream, a plurality of control bits, and a predefined fill word bit pattern; forming a frame by combining the bits of the selected 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 bits 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 frames such that the master transition is not always immediately preceded or immediately followed by another transition; and if the selected word is a data word or a control word, 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. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification