Abstract: A microcontroller fabricated on a semiconductor chip is adapted, when operating, to execute programs and instructions and, in response, to generate control signals to selectively control external apparatus. A clock generates timing signals to control the timing of the microcontroller execution and operation. An on-chip program memory has space avilable for storing a program to be executed by the microcontroller in sequential steps in successive address locations of the program memory. An instruction stored in unerasable memory on the chip initiates self-programming of the program memory with the program to be executed by the microcontroller by enabling a pointer timed by the clock to alternately read addresses containing steps of the program to be executed from off-chip memories and to write same into successive addresses of the on-chip program memory by incrementing the latter addresses with each step to be written therein.

Abstract: 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.