A technique for downloading data from a processor unit, such as an inverter control computer associated with a locomotive control system. When the software for the inverter control computer is originally built, a programmer assigns an ID number to all of the possible instrumentation signals that can be downloaded from the inverter control computer. From the complete list of the instrumentation signals, the programmer defines a default set of the instrumentation signals that are downloaded. If a user wishes to change the instrumentation signals that can be downloaded, then the user provides a command signal to the inverter control computer that changes the set of ID numbers of the instrumentation signals to be downloaded.