GB1481008A - Digital data transmission systems and apparatus therefore - Google Patents

Abstract

1481008 Data transmission; D.C. suppression GENERAL ELECTRIC CO Ltd 27 Sept 1974 [29 June 1973] 30995/73 Heading H4P In an arrangement to reduce disparity in a system in which n bit input words are converted into n - 1 digit ternary words having different disparities with a result that there are 2 alternative conversions for some binary words and a ternary word representing any binary word according to one ternary code is the inverse of an another ternary word corresponding to the complement of the binary word, a simplification is made by providing a single coding matrix 6 controlled by a circuit 14 which switches at 4 the input binary word to its complement, and simultaneously from the matrix output the corresponding ternary word to its inverted value at 8, the control circuit 14 selecting the normal or complement/inverted mode in dependence on cumulative disparity and the digit value of a part, but not all of the binary word. In the embodiment described only a single digit of the binary words are used and n=4. A table (not shown) is provided in the Specification giving 3 ternary codes for each 4-bit word with the basis that: The first digit "0" ternary code II equals ternary code III first digit "1" ternary code II equals ternary code I. Instead of the first digit of each binary word being utilized, a corresponding signal from switching unit 4 may be used, passed through a further switch to bring it to its original value, but any other binary digit may be used with appropriate modification of the table. Preferably the ternary words for "0000" and "1111" are not changed so as to enable word misalignment to be detected.