US5446864A — System and method for protecting contents of micr…

Claim 1

Independent Claim 231 words

A microcontroller fabricated on a semiconductor chip to execute programs and instructions and, in response, to generate control signals to selectively control external apparatus, comprising: an on-chip EPROM program memory, and mode selecting means for selectively configuring the microcontroller to operate in any one of a plurality of predetermined operating modes, including at least one secure microcontroller mode, said mode selecting means including: a plurality of EPROM configuration fuses mapped into the on-chip EPROM program memory as bits in respective address locations thereof, each bit having a value of "1" or "0", the value of a bit representing any one of said fuses reflecting a state of being either erased or blown, respectively, for the respective fuse, means for configuring the microcontroller by programming the bits in address locations of said EPROM program memory representing selected fuses in said EPROM program memory so that each fuse is either blown or erased according to a selected configuration, and means for making address locations of fuses in said EPROM program memory inaccessible for reading or writing except in said at least one secure microcontroller mode such that when in said at least one secure microcontroller mode any attempt to read an address location within said EPROM program memory that is executed externally from said EPROM program memory results in reading scrambled data and wherein the contents of said EPROM program memory are unaltered.

Claim 2

Dependent Claim 231 words

A microcontroller fabricated on a semiconductor chip to execute programs and instructions and, in response, to generate control signals to selectively control external apparatus, comprising: an on-chip EPROM program memory, and mode selecting means for selectively configuring the microcontroller to operate in any one of a plurality of predetermined operating modes, including at least one secure microcontroller mode, said mode selecting means including: a plurality of EPROM configuration fuses mapped into the on-chip EPROM program memory as bits in respective address locations thereof, each bit having a value of "1" or "0", the value of a bit representing any one of said fuses reflecting a state of being either erased or blown, respectively, for the respective fuse, means for configuring the microcontroller by programming the bits in address locations of said EPROM program memory representing selected fuses in said EPROM program memory so that each fuse is either blown or erased according to a selected configuration, and means for making address locations of fuses in said EPROM program memory inaccessible for reading or writing except in said at least one secure microcontroller mode such that when in said at least one secure microcontroller mode any attempt to read an address location within said EPROM program memory that is executed externally from said EPROM program memory results in reading scrambled data and wherein the contents of said EPROM program memory are unaltered.

Claim 3

Dependent Claim 29 words

The invention of claim 1, further including: means for reading the state of each fuse by reading the value of its respective bit stored in said EPROM program memory.

Claim 4

Dependent Claim 34 words

The invention of claim 1, wherein: said mode selecting means further includes means for programming the fuses by selectively writing to the address location of the respective fuse in the on-chip EPROM program memory.

Claim 5

Dependent Claim 210 words

A microcontroller fabricated on a semiconductor chip to execute programs and instructions and, in response, to generate control signals to selectively control external apparatus, comprising: an on-chip EPROM program memory, security means for preventing read, verify or programming of any address location in said on-chip EPROM program memory from a location external to said on-chip EPROM program memory, said security means including fuses represented by predetermined address locations of said EPROM program memory, each address location containing a bit having a value of either "1" or "0", wherein each fuse has states of being either erased or blown, respectively, according to the value of the bit at the respective address location representing that fuse, and means for selectively reading and programming the bits in at least some of said address locations representing the fuses to implement the security, and means for making address locations of fuses in said EPROM program memory inaccessible for reading or writing except in at least one secure mode such that when in said at least one secure mode any attempt to read an address location within said EPROM program memory that is executed externally from said EPROM program memory results in reading scrambled data and wherein the contents of said EPROM program memory are unaltered.

Claim 6

Dependent Claim 210 words

A microcontroller fabricated on a semiconductor chip to execute programs and instructions and, in response, to generate control signals to selectively control external apparatus, comprising: an on-chip EPROM program memory, security means for preventing read, verify or programming of any address location in said on-chip EPROM program memory from a location external to said on-chip EPROM program memory, said security means including fuses represented by predetermined address locations of said EPROM program memory, each address location containing a bit having a value of either "1" or "0", wherein each fuse has states of being either erased or blown, respectively, according to the value of the bit at the respective address location representing that fuse, and means for selectively reading and programming the bits in at least some of said address locations representing the fuses to implement the security, and means for making address locations of fuses in said EPROM program memory inaccessible for reading or writing except in at least one secure mode such that when in said at least one secure mode any attempt to read an address location within said EPROM program memory that is executed externally from said EPROM program memory results in reading scrambled data and wherein the contents of said EPROM program memory are unaltered.

Claim 7

Dependent Claim 42 words

The invention of claim 4, further including means for configuring said microcontroller in said at least one secure mode by selectively setting the value of the bit in at least one address location in said EPROM program memory representing a preselected fuse.

Claim 8

Independent Claim 207 words

A method of protecting program data written in EPROM program memory of a microcontroller fabricated on an integrated circuit chip in which the EPROM program memory is embedded, from unauthorized access or alteration, the method comprising the steps of: mapping programmable configuration fuses into a number of distinct and different ones of respective address locations, said number being much smaller than the total number of address locations of the embedded EPROM program memory, as bits having respective values of either "0" or "1" representing a blown state or an erased state of the respective fuse, securing said embedded EPROM program memory against access from an address location external to said embedded EPROM program memory by programming at least one of said bits to a predetermined state of the respective fuse to prevent reading from or writing to the embedded EPROM program memory from any location external to said embedded EPROM program memory, making address locations of fuses in said embedded EPROM program memory inaccessible for reading or writing except in at least one secure mode and scrambling data read from said embedded EPROM program memory from a location external to said embedded EPROM program memory and wherein the contents of said embedded EPROM program memory are unaltered.

Claim 9

Independent Claim 207 words

A method of protecting program data written in EPROM program memory of a microcontroller fabricated on an integrated circuit chip in which the EPROM program memory is embedded, from unauthorized access or alteration, the method comprising the steps of: mapping programmable configuration fuses into a number of distinct and different ones of respective address locations, said number being much smaller than the total number of address locations of the embedded EPROM program memory, as bits having respective values of either "0" or "1" representing a blown state or an erased state of the respective fuse, securing said embedded EPROM program memory against access from an address location external to said embedded EPROM program memory by programming at least one of said bits to a predetermined state of the respective fuse to prevent reading from or writing to the embedded EPROM program memory from any location external to said embedded EPROM program memory, making address locations of fuses in said embedded EPROM program memory inaccessible for reading or writing except in at least one secure mode and scrambling data read from said embedded EPROM program memory from a location external to said embedded EPROM program memory and wherein the contents of said embedded EPROM program memory are unaltered.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1998-08-28	1999-02-27	1999-08-29	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2002-08-28	2003-02-27	2003-08-29	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2006-08-28	2007-02-27	2007-08-29	$7700.00	Window Closed / Lapsed

System and method for protecting contents of microcontroller memory by providing scrambled data in response to an unauthorized read access without alteration of the memory contents

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