Texas Instruments Corporation

Gregory B Davis

Eric G Soenen

Thomas F Adkins

Russell K MacDonald

Angie Dycus

An integrated circuit (IC) configurable as transmitter/receiver includes a method of preventing unauthorized learning and reproduction of an access code as a security measure. When the IC is configured as a receiver and placed in the learn mode, a flag is set in a memory of a microcontroller. If later configured as a transmitter, the microcontroller checks the flag upon power up and if the flag is set, the stored code is randomized so transmission of it is impossible.

Method of preventing unauthorized reproduction of a transmission code

An integrated circuit configurable as a transmitter/receiver includes learn capabilities that allows a receiver IC to memorize the identification pattern of a specific transmitter.

Combined transmitter/receiver integrated circuit with learn mode

A remote control access system uses a transmitter and a receiver. The transmitter generates an encrypted identification code which the receiver decrypts and grants access to the system if the decrypted code matches an identification code stored in the receiver. The encryption occurs by taking a 40 bit identification code and forming 5 bytes (8 bytes each). The 5 bytes are logic exclusive OR'd to form a 5 byte wide encrypted code. Decryption occurs by performing the opposite exclusive OR operation on the 5 byte wide encrypted code to convert it back to the 5 byte identification code. The 4 most significant bytes of the decrypted code are compared against the 4 most significant bytes of the previous stored decrypted code in the receiver. If the comparison yields a zero, this means the least significant byte will be within 2.sup.8 or 256 of each other and access will be granted.

Rolling code identification scheme for remote control applications

A transmitted data stream in a remote control system is a serial data stream having a synchronization sequence and a data sequence. The data sequence is encoded into a symbol comprised of a series of data bits wherein a 110 may represent a logic 1 and a 011 may represent a logic 0. A self adaptive filter adjusts its gain and offset to determine the duration of one bit. Providing a serial code format wherein the synchronization sequence has a smiller duty cycle as the duty cycle of a symbol aids the self adaptive filter to set its threshold switching level accurately and quickly, thus aiding the receiver to decode the transmitted data stream.

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Allen, TX, United States of America

Gregory B Davis