Method and apparatus for preventing unauthorized access to nonvolatile memory in electronic encoders having a voltage level detection circuit

• US 5,675,534 A
• Filed: 03/05/1996
• Issued: 10/07/1997
• Est. Priority Date: 03/05/1996
• Status: Expired due to Term

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Smit, Willem, Hewitt, Kent
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Tran, Andrew Q.
• Application Number:
  US08/611,993
• Time in Patent Office: 581 Days
• Field of Search: 365/185.04, 365/189.09, 365/196, 365/195, 365/228, 235/382, 340/825.31, 340/825.34
• US Class Current: 365/185.04
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells

Abstract

According to the present invention, a method is provided for reading data from non-volatile memory in an electronic encoding device such that unauthorized access to the data is prevented. In one embodiment, the method includes the steps of writing a first set of data to the non-volatile memory; generating a voltage detect signal during the writing, the voltage detect signal being representative of a source voltage applied to the non-volatile memory; determining whether the writing was successful by evaluating the voltage detect signal; and reading data from the non-volatile memory responsive to the determination.

Claims

1. A method for reading data from non-volatile memory in an electronic encoding device such that unauthorized access to the data is prevented, the method comprising:

writing a first set of data to the non-volatile memory;

generating a voltage detect signal during the writing, the voltage detect signal being representative of a source voltage applied to the non-volatile memory;

determining whether the writing was successful by evaluating the voltage detect signal;

reading data from the non-volatile memory responsive to the determination.

2. A system for reading data from non-volatile memory in an electronic encoding device such that unauthorized access to the data is prevented, the system comprising:

means for writing a first set of data to the non-volatile memory;

means for generating a voltage detect signal during the writing, the voltage detect signal being representative of a source voltage applied to the non-volatile memory;

means for determining whether the writing was successful by evaluating the voltage detect signal; and

means for reading data from the non-volatile memory responsive to the determination.

3. An electronic encoding device comprising:

a non-volatile memory;

a controller coupled to the non-volatile memory;

encoder logic coupled to the non-volatile memory;

input logic coupled to the controller;

output logic coupled to the non-volatile memory; and

a voltage level detection circuit coupled to the non-volatile memory, which provides a signal responsive to a non-volatile memory write voltage to enable a read from said non-volatile memory.

4. An electronic encoding device as in claim 3 wherein the voltage level detection circuit comprises:

a pair of series connected P-channel transistors, each transistor having a first threshold voltage;

an N-channel transistor having a second threshold voltage;

the N-channel transistor being in series with the pair of P-channel transistors;

a voltage detect signal path connected between a source of the N-channel transistor and the controller.

5. A method for reading data from non-volatile memory in an electronic encoding device such that unauthorized access to the data is prevented, the method comprising:

writing a first set of data to the non-volatile memory;

generating a voltage detect signal during the writing, the voltage detect signal being representative of a write voltage applied to the non-volatile memory;

determining whether the writing was successful by evaluating the voltage detect signal;

reading data from the non-volatile memory responsive to the determination.

6. An electronic encoding device comprising:

and non-volatile memory;

a controller coupled the non-volatile memory;

encoder logic coupled to the non-volatile memory;

input logic coupled to the controller;

output logic coupled to the non-volatile memory; and

a voltage level detection circuit coupled to the non-volatile memory, which provides a signal responsive to a source voltage applied to the non-volatile memory, during writing to said non-volatile memory the signal being enabling of a read from said non-volatile memory.