Abstract: A microcontroller device on a single integrated circuit including a central processing unit, an associated data bus and an electrically-programmable nonvolatile memory is disclosed. The nonvolatile memory contains the applications program and may be remotely programmed by way of a communication port, such as a universal asynchronous, receiver/transmitter (UART) device, utilizing a separate host computer. A second nonvolatile memory is provided which contains a control program which is executed by the central processing unit for carrying out the programming of the electrically-programmable nonvolatile memory utilizing data and address information received from the host computer over the communications port.

Abstract: An encryption method is taught which chooses certain bytes of data, stored in a particular on-chip memory, as encryption keys. These chosen bytes are used to encrypt themselves, and all of the remaining data in the above mentioned particular memory. The chosen bytes do not have values specifically assigned for encryption, they are merely chosen, according to a rule, from the body of data to be encrypted. When this technique is implemented, each byte of data, stored in the mentioned memory, is combined (for example using an exclusive NOR gate) with one of the designated encryption key bytes prior to disclosure. The user is not required to provide, program, or safeguard a set of key bytes separately. Additionally, no silicon area is wasted in storing such bytes. An intruder would need certain pieces of the original data in order to decipher the results of this encryption technique. Additionally, this technique degrades gracefully.