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 .