is followed by a code beginning with a 0 bit (1, 4, 5, 6, 7), so will always appear separated by multiples of the 5-bit encoded symbol length (and never separated by a single symbol). Violations of this property are used for special synchronization codes. Command characters The following codes are sometimes referred to as command characters. They are commonly used in pairs, although USB-PD uses 4-symbol sequences to begin its packets. See also GCR 4B-5B encoding References External links Simulator - 4B/5B Encoder line written in Matlab CodSim 2.0: Open source simulator for Digital Data Communications Model at the University of Malaga written in HTML Telecommunications standards Line codes