An electronic device for storing protected data is disclosed. The electronic device includes memory protection logic operable to interface with memory, such as non-volatile ROM for storing protected data therein. The protected data in one embodiment is program code. The access to the protected data is restricted by a local processor, such as a microcontroller or microprocessor for execution thereon within the electronic device. Further, the electronic device includes validation logic operative in a first mode, for checking the validity of the data and for producing a validity signal, such as a checksum, enabled to determine whether that data is valid. In order to prevent access to intermediate validity calculations which may allow an individual to gain knowledge of the protected data, a validity signal output control is provided for inhibiting an output of the validity signal to outside the device until the validity of a predetermined quantity of the protected data has been checked. This predetermined quantity is made sufficiently large and preferably equal to all of the protected data. In another embodiment, a reset for setting the contents of the validity signal if the checking is interrupted is also included.