This document specifies the line code 4b/10b for dependable multimedia signal transmission required for complex machines@ such as robots and automobiles. This document corresponds to the functions specified in layer 1 to layer 2 of the OSI reference model (ISO/IEC 7498). The purpose of this document is to facilitate the development and use of the 4b/10b in dependable systems by providing a line code protocol. This document provides a line code protocol for interconnections among distributed real-time systems@ including embedded systems@ control systems@ amusement systems@ robot systems@ and intelligent buildings. The 4b/10b can achieve the line code with ECC (error code correction). The 4b/10b is the line code that realizes embedded clock@ DC balance@ error detection and error correction at a time; it is not possible to satisfy these functions in one codec by conventional schemes@ and the 4b/10b line code can achieve highly reliable and dependable digital communications.