Static information storage and retrieval – Floating gate – Data security
Reexamination Certificate
2002-08-23
2004-07-20
Yoha, Connie C. (Department: 2818)
Static information storage and retrieval
Floating gate
Data security
C365S185050, C365S189040, C365S189050, C365S201000, C365S228000
Reexamination Certificate
active
06765826
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an electronic assembly with at least one non-volatile memory device that includes a controllable write protect terminal.
Configuration data and operating parameters of electronic assemblies are often stored in non-volatile memory devices located on the assemblies. These non-volatile memory devices are programmed with configuration data and operating parameters at a test location at the factory before the assembly is mounted in a target system. In the target system, the operating parameters and the configuration data are read by a higher-ranking unit of the target system. But they usually must not be modified in the target system.
EEPROMs (Electrically Erasable Programmable Read Only Memories) are customarily utilized as such non-volatile memory devices. Such EEPROMs can be repeatedly written to. EEPROMs are usually capable of one of two methods of preventing unintentional or unauthorized writing.
The first possibility is to protect the contents of the EEPROM against further writing by using a special programming mode.
The second common method of protecting commercial EEPROMs against unauthorized writing involves a write protect terminal. The contents of the EEPROM are protected against overwriting as long as a first signal at the write protect terminal has a level which activates the write protection. Writing is possible only when the signal at the write protect terminal is the inverse of the first signal. The write protect terminal can be high-active or low-active.
For storing the data of a recent maintenance or data for reconfiguring the assembly, operating parameters and configuration data must be kept on an electronic assembly in a reparameterizable form.
On the other hand, any modification of these data in the target system must be prevented. Misoperations or, when the target system is a computer, viruses may render the assembly unusable for long periods of time or may damage the computer by overwriting these data.
Hitherto the write protection of non-volatile memory devices on electronic assemblies has been handled according to one of the following methods:
An operating system in the target system provides for a programming operation in the non-volatile memory devices with each startup operation of the target system. This programming operation prevents further writing of the non-volatile memory devices. All unwanted write operations in the target system are thus prevented, but possible wanted write operations at a test location outside the target system are also prevented.
According to other proposals (U.S. Pat. No. 5,661,677 and U.S. Pat. No. 5,859,792), the write protect terminal of the non-volatile memory device is connected temporarily or permanently to a special terminal of the assembly. The overwriting of the data of the non-volatile memory device in the target system can be prevented by connecting this special terminal in the target system to a potential that activates the write protection. At another mounting location, for instance, at the test device, a potential that deactivates the write protection is applied at this terminal. Operating parameters and configuration data are protected in the target system and are reparameterizable outside the target system. The disadvantage of this possibility is the fact that an additional special terminal for operating the write protection is needed at the assembly.
In order to guarantee the operating reliability of the target system, the previous methods for handling the write protection on non-volatile memory devices thus require either that the reparameterizability of the electronic assembly be forgone or that an additional special terminal be provided on this assembly.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an electronic assembly with a non-volatile memory device and a method for writing to a non-volatile memory device with a write protect terminal which overcomes the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to provide write protection for non-volatile memory devices on electronic assemblies, such that the non-volatile memory devices that are write-protected in a target system can be written to at a test location.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic assembly, in combination with a target system and a test location. The electronic assembly includes: at least one non-volatile memory device having a write protection feature and a controllable write protection terminal for activating and deactivating the write protection feature; at least one additional semiconductor device; a terminal device including at least one pair of supply terminals for supplying the non-volatile memory device and at least one third supply terminal for supplying the additional semiconductor device when the electronic assembly is being operated in the target system; a first signal path; and a switching configuration connecting the write protect terminal of the non-volatile memory device to the third supply terminal over the first signal path. The third supply terminal provides a potential for activating the write protection feature when the electronic assembly is being operated in the target system. The write protection feature is deactivatable when the electronic assembly is being operated at the test location.
In accordance with an added feature of the invention, the switching configuration includes a permanent connection.
In accordance with an additional feature of the invention, the switching configuration connects the write protection terminal of the non-volatile memory device over a second signal path to a first one of the pair of the supply terminals; and the write protection feature is deactivated by a potential on the first one of the pair of the supply terminals.
In accordance with another feature of the invention, the switching configuration includes at least one component for interrupting the first signal path or the second signal path.
In accordance with a further feature of the invention, the switching configuration includes passive elements with connections; and the passive elements derive valid signal levels for activating and deactivating the write protection feature from potentials at the supply terminals.
In accordance with a further added feature of the invention, the switching configuration includes active elements; and the active elements derive valid signal levels for activating and deactivating the write protection feature from potentials at the supply terminals.
In accordance with yet an added feature of the invention, the non-volatile memory device is an EEPROM.
In accordance with yet an additional feature of the invention, the electronic assembly is a memory module.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for writing to at least one non-volatile memory device having a write protection feature and a controllable write protection terminal. The method includes steps of:
(a) providing the non-volatile memory device on an electronic assembly having at least one pair of supply terminals for supplying the non-volatile memory device, at least a third supply terminal, and a switching configuration;
(b) mounting the assembly at a test location;
(c) at the test location, driving the third supply terminal of the assembly in a particular way such that the switching configuration generates a signal that deactivates the write protection feature;
(d) writing to the memory device;
(e) mounting the assembly in a target system;
(f) in the target system, feeding-in a potential at the third supply terminal of the assembly, from which the switching configuration generates a signal that activates the write protection feature; and
(g) frequently repeating steps (a) to (f).
In accordance with an added mode of the invention, the method includes steps of: at the test location, feeding-in a po
Kiehl Oliver
Ruckerbauer Hermann
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Stemer Werner H.
Yoha Connie C.
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