Abstract: In many applications, for example in a telecommunications system, it is necessary to identify a unique data sequence at a high speed serial data interface within one bit period of the complete sequence being received. This pattern recognition is often used in order to synchronize the receiver to the frame timing of an incoming data stream and thus identify the octet boundaries. It is usually required to react to this pattern within one data bit period at the interface in order to synchronize internal counters. A data stream pattern recognition apparatus recognizes a predetermined pattern of sequential data within a data stream by including a state machine having at least as many state units connected in series as there are bits in the predetermined pattern, the state machine transfers sequentially from state to state on receipt of each bit of the series.