An electronic data storage medium is adapted to be accessed by a data terminal, and includes a processing unit connected to a memory device that stores a data file and security reference data possessed by a person authorized to access the data file, and an input-output interface circuit activable so as to establish communication with the data terminal. The processing unit is operable selectively in a programming mode and a data retrieving mode. The electronic data storage medium also includes a function key set for manually switching the electronic data storage medium between the programming mode and the data retrieving mode.