Abstract: To test the performance of an analog/digital converter, used for translating bipolar message signals into 8-bit words, the analog input of the converter is connected across a voltmeter while its digital output works into a buffer register distributing the seven amplitude bits of an emitted code word to one set of stage inputs of a comparator having another set of stage inputs connected to a manually operable word simulator; the sign bit of the code word is entered in a separate store. A logic network with inputs connected to the sign-bit store, the comparator and the word simulator controls two reversible counters which, upon manual operation of the word simulator, emit selected numerical values translated by associated digital/analog converters into output signals fed to the analog/digital converter to be tested.