Prevention of alteration of data stored in secure integrated circuit chip memory

An integrated circuit chip (10) in which alteration of secure data stored in a predetermined location of a memory (M) on the chip may be prevented. In one embodiment (FIG. 1), the chip (10) includes a memory (M) having a plurality of memory locations, with a predetermined location being for the storage of unalterable secure data; a memory control logic circuit (38) coupled to the memory by an address bus (46) for causing data to be stored in locations of the memory indicated by address signals provided on the address bus; a fuse element (42) having an initial state and an irreversibly altered state; means (44) coupled to the fuse element for irreversibly altering the state of the fuse element in response to a predetermined control signal (48); and a decoder (40) coupled to the fuse element, the memory control circuit and the address bus for monitoring the state of the fuse element and said address signals, and for preventing the memory control circuit from causing data to be stored in the predetermined memory location after the state of the fuse element has been altered irreversibly whenever the predetermined memory location is indicated by an address signal on the address bus. In another embodiment (FIG. 2), the chip (10), includes a first memory (M) having a plurality of memory locations, with a predetermined location being for the storage of unalterable secure data; a second memory (52); means (55) for enabling a data pattern to be stored in the second memory; a memory control logic circuit (54) coupled to the first and second memories for causing data to be stored in the predetermined location of the first memory in response to a write signal whenever the second memory contains a predetermined data pattern; means (66) coupled to the second memory for enabling the contents of the second memory to be erased; a fuse element (56) having an initial state and an irreversibly altered state; and means (58) coupled to the fuse element for irreversibly altering the state of the fuse element in response to a predetermined control signal (67); wherein the fuse element is coupled to the means for enabling a data pattern to be stored in the second memory so as to enable said data pattern storage only prior to the state of the fuse element being irreversibly altered.