Self initializing phase locked loop ring communications system

Abstract

A communications network including a plurality of terminals coupled together to provide a unidirectional communications ring. Each of the terminals is coupled in series along the ring. Each terminal is adapted to transmit (at an associated data rate) a digital signal to the next downstream terminal on the ring. Each terminal is adapted to receive a digital signal at the data rate associated with the next upstream terminal. The received digital signal is applied to a phase locked loop characterized by a hold time which exceeds its lock time. The phase locked loop extracts a local timing signal for re-clocking the received digital signal. The transmission time of N bits is less than the hold time of the phase locked loop. Each terminal monitors the re-clocked signal to identify when same valued consecutive bits are received for a period less than the phase locked loop hold time, and upon such detection to cause that terminal to generate at least one transition.