an optical code recognition unit for recognizing a predetermined n - bit optical code has an n - way splitter having an input and n parallel outputs . a plurality of combiners are associated with the splitter outputs , and a respective gate is controlled by the output of each of the combiners . each of the splitter outputs is subject to a different delay of from 0 to bit periods , and each combiner receives an input from at least one of the splitter outputs . the ocru is such that all the gates are turned on if a predetermined optical code is applied to the splitter input .