US 4,517,552 A · Method and apparatus for N-to-M encoding

Abstract

A method and apparatus are provided for encoding successive n-bit information words into successive m-bit code words wherein m>n. Each n-bit information word is assigned with a respective set of m-bit code words. Each set of code words is comprised of either two or four words. The words in each two-word set have zero disparity, and their first bits are of opposite logical sets. In the four-word sets, two words have positive disparity and their first bits are of opposite logical sense, and the other two words have negative disparity and their first bits also are of opposite logical sense. The particular m-bit code word that is selected from the set associated with the n-bit word commences with the same bit as the last bit of the immeditely preceding code word, and the selected code word exhibits a disparity that, when combined with the digital sum variation of the preceding encoded code words, reduces the overall digital sum variation toward zero.

Claims22

Dependent claims

A method of encoding successive n-bit information words into successive m-bit words having a minimum interval between bit transitions of at least 2T (where T is the bit interval of each code word), and a predetermined maximum interval between bit transitions, and wherein m>n, comprising the steps of storing for each n-bit information word a respective set of m-bit code words, each of predetermined ones of said sets being formed of two code words having zero disparity and one of said two code words commencing with a binary "0" bit and the other commencing with a binary "1" bit, and each of the remaining ones of said sets being formed of four code words, two of said four code words having positive disparity and commencing with binary "0" and binary "1" bits, respectively, and the remaining two code words having negative disparity and commencing with binary "0" and binary "1" bits, respectively;

identifying in each set of code words assigned to an input information word those code words commencing with the same bit as the last bit of the immediately preceding code word;
and addressing among the selected code words the code word whose disparity, when combined with the digital sum variation of the preceding encoded code words, reduces the overall digital sum variation of the encoded code words toward zero.

A method of encoding successive n-bit information words into successive m-bit code words, wherein m>n, comprising the steps of storing 2.sup.n sets of m-bit code words, each set representing a respective n-bit information word with predetermined ones of said sets each including two code words of zero disparity and having first bits of opposite logical sense, and with the remaining sets each including four code words, two of which have positive disparity and first bits of opposite logical sense and the other two of which have negative disparity and first bits of opposite logical sense;

and addressing the stored code words to select a predetermined m-bit code word by using the n-bit information word to address the set of code words representative thereof, using the last bit of the preceding selected code word to address at least one of the code words in the addressed set whose first bit exhibits a predetermined relationship with said last bit, and using the digital sum variation of the preceding successing code words to address said at least one code word whose disparity, when combined with said digital sum variation, tends to reduce said digital sum variation toward zero.

Apparatus for encoding successive n-bit information words into successive m-bit code words, wherein m>n, comprising input means for receiving an n-bit information word;

means responsive to the received information word for selecting a set of code words including at least two m-bit code words each representative of said information word, said at least two code words having first bits of opposite sense and disparities of equal absolute magnitude, and each of said code words having at least two consecutive interior bits of the same logical sense;
means for detecting the last bit of the preceding code word;
means for determining the digital sum variation of the preceding successive code words;
and means responsive to the detected last bit and determined digital sum variation for designating the m-bit code word in said selected set whose first bit is of the same logical sense as said detected last bit and whose disparity when combined with said determined digital sum variation reduces the digital sum variation toward zero.

1 more element

Dependencies are inferred from the claim text.

Method and apparatus for N-to-M encoding

Life of this patent

Method and apparatus for N-to-M encoding

Life of this patent

Abstract

Claims22