Abstract: The invention relates to data generators producing output signals representative of data and in compliance with a predetermined telecommunications standard. A generator of the invention comprises a memory device programmed with data which produces signals representing control bits for controlling the configuration of output data, e.g. frame and multiframe synchronization signals, and additional signals which control a sequence generator producing a sequence of data to be inserted in the data pattern. Operation is completely programmable and may be adapted to numerous different telecommunications standards. The invention is applicable to testing telecommunications networks.