Abstract

A coding method and apparatus convert a data word of m×r bits into a code word of n×r bits (m<n) with regard to a predetermined number r. The basic data word length m is made two or three bits, basic code word length n is made five bits and the predetermined number r satisfies the relation 1ࣘrࣘ4 or 1ࣘrࣘ2 respectively, the data word of m×r bits is converted into a code word of 5r bits, and coding is performed in such a manner that the run number of "0"s is greater than four and less than 19, or greater than one and less than five respectively. Further, a decoding method and apparatus decode perform decoding in accordance with the logical expressionsY1 =X13 +X14 ⋅(X19 +X20)+X9 ⋅X10 ⋅X15 +X9 ⋅X10 ⋅X11 ⋅X12 ⋅X13 ⋅14 +(X4 +X5)⋅X10 ⋅X15Y2 =X12 +X13 +X14 +X15 +X4 ⋅(X9 ⋅X14 +X10)⋅X15where X1 -X20 represents the bit series of a code word coded in such a manner that a data word of 2×γ bits is converted into a code word of 5×γ bits, where basic data word length m of a digital signal is two bits, basic code word length n is five bits and γ is an integer, and such that a run length of "0"s between a "1" and a "1" of a binary code word pattern obtained by interconnecting the code words following conversion is greater than 4, and γ satisfies the relation 1 ࣘγࣘ3, Y1, Y2 represent a bit series of a decoded data word, and X indicates the inverted value of a bit.