Abstract: The code word recognition unit (51) comprises an optical switching element which can be controlled electrically and serves as a light switch, a sequence generator (75) for electrically controlling the switching element (57), an optoelectrical transducer (60), an electrical integrator (63), a threshold circuit (66) and a control unit (69). In addition, there is a clock generator (72) and a decision unit (73).Code words appear periodically at the input (53) as optical bit patterns (OM) which are synchronized with an assigned electrical comparison pattern (VM) at the control input (44). The light let through by the switching element (57) forms a voltage pulse (U) via the transducer (60) at the integrator (63), the level of the voltage pulse (U) forming a measurement for the agreement of the two patterns (OM, VM). If the two patterns agree, there is a clear maximum.The code word recognition unit (51) serves for the rapid recognition of address codes on optical lines.