Abstract: A data processing system has at least one processing module containing one or more blocks of memory, having control registers which are accessible via a diagnostic interface, and a clock module which distributes system clocks to the processing module(s), the operation of which is controllable using a similar diagnostic interface. One of the possible actions in the clock module is the generation of a single-shot clock pulse. A diagnostic control unit is connected to the separate diagnostic interfaces of the processing module(s) and the clock module, and is capable of simultaneously controlling the two diagnostic interfaces in such a way that a single-shot clock pulse can be synchronized with the diagnostic access to a processing module to effect the loading or dumping of a block of memory line by line.