Ray A Allen, 757513 Whitaker Ave, Van Nuys, CA 91406

5455937, Oct 3, 1995

Jun 30, 1994

8/268673

Eric Berman - Hicksville NY
Greg Italiano - Hicksville NY
Ajay Padgaonkar - Sugarland TX
Ray Allen - Mesa AZ

Microchip Technology, Inc. - Chandler AZ

G11C 700
G01R 3128

395500

A microcontroller fabricated on a semiconductor chip has an on-chip EPROM program memory with programmable EPROM configuration fuses located in a limited number of addresses of the on-chip program memory, the condition of each of EPROM fuse being defined as blown or not blown according to the value of the bit stored in the respective address of the on-chip program memory. The operating modes of the microcontroller are configurable by appropriately programming at least some of the EPROM fuses. Testing of the microcontroller in at least some of the operating modes is achieved by using latches outside the program memory to emulate the EPROM fuses, while suppressing the capability to set the condition of the EPROM fuses during the testing. Upon completion of the testing, control of the operating modes of the microcontroller is returned to the EPROM fuses, and the latches are precluded from further emulating the EPROM fuses.

5446864, Aug 29, 1995

Mar 7, 1994

8/207886

Martin Burghardt - Oberneuching, DE
Eric Berman - Hicksville NY
Ajay Padgaonkar - Sugarland TX
Ray Allen - Mesa AZ

Microchip Technology, Inc. - Chandler AZ

G06F 1214

395427

A microcontroller fabricated on a semiconductor chip has an on-chip EPROM program memory. The microcontroller is selectively configurable to operate in any one of a plurality of predetermined operating modes, including at least one secure microcontroller mode. A plurality of EPROM configuration fuses used for configuring the microcontroller and protecting its program memory from read, verify or write through any instruction initiated from other than a predetermined secure area of the chip, are mapped into the on-chip EPROM program memory as bits in respective address locations thereof. The value of a bit representing any one of said fuses is effective to determine the condition of the respective fuse. That condition is observed by reading the value of the respective bit for that fuse stored in the EPROM program memory. The chip security is enabled by configuring the microcontroller in a code protected mode by programming the bits representing the desired fuses in the EPROM program memory to effectively blow or erase each fuse according to the desired configuration.