Method and circuit for protecting circuit configurations having an electrically programmable non-volatile memory
AssigneeSiemens Aktiengesellschaft
InventorHartmut Schrenk
Life of this patent
Estimating the term…
Abstract
In a method and circuit for protecting circuit configurations having an electrically programmable non-volatile memory used as a non-volatile counter, an access check is provided in the circuit configuration by comparison of a check code to be fed in with a secret code. Each counter bit is evaluated immediately after programming the counter bit. A protected function is disabled in dependence on the recognition of the counter bit as written. The reading level is set during the evaluation of a particular counter bit to be more-critical than in all of the later reading operations of the counter bit.
Claims4
Circuit for protecting circuit configurations having an electrically programmable non-volatile memory divided into a plurality of memory regions, wherein one of said regions is used as a non-volatile error counter for counting error check data, comprising a level flipflop, a level switching device connected to said level flipflop, and a logic circuit connected to said level flipflop;
- said level switching device having an output connected to a programming control input of said non-volatile memory, and furnishing an evaluation level set between a normal level and a more-critical level as a function of the switching state of said level flipflop;
- said level flipflop being connected to an output of said non-volatile memory for preventing unwanted manipulation of said error counter by setting a more-critical evaluation level at said output of said level switching device;
- said logic circuit furnishing a disable signal in dependence on the logical state of the selected memory cell for disabling the performance of the protected function.
Method for protecting a circuit configuration having a non-volatile counter operating as an electrically programmable non-volatile counter, the counter having a normal and a critical reading level, wherein the circuit configuration provides access control by means of a protective function by comparing control data to be entered and compared with a secret code stored in the non-volatile memory, the method which comprises the steps of:
- (a) after each comparison, programming a counter bit into the non-volatile counter;
- (b) testing, immediately following the programming of a respective counter bit, if the programming has been correctly performed, wherein the testing is performed by reading the respective counter bit with a more critical reading level;
- (c) disabling, in case the respective counter bit is determined by the test as being correctly programmed a protective function, or
- (d) preventing, in case the respective counter bit is determined by the test as not being correctly programmed, disabling of the protective function.
Dependencies are inferred from the claim text.