Abstract: Access to a vehicle by a remote electronic key via a radio link is secured by an exchange of encrypted signals. A remote unit having a secret number is introduced to a base unit and a common key is agreed upon by an exponential key exchange. The common key is encrypted using the secret number and stored in the base unit. Thereafter, the base unit is able to authenticate the identity of the remote unit by sending the encrypted common key and a random number to the remote unit which decrypts the key and uses it to encrypt the random number. The random number is also encrypted in the base unit and compared with the encrypted random number from the remote unit.

Abstract: An automobile radio receiver system includes a control unit located in the passenger compartment and a remote unit, for example, in the trunk compartment of the automobile. The control unit includes a master microcomputer which controls a display and responds to keyboard inputs. The remote unit includes the radio receiver which is controlled by a slave microcomputer. The master and slave microcomputers are interconnected by a single wire data bus. Data regarding keyboard inputs are transmitted to the slave and data regarding receiver status is transmitted to the master. The data is interleaved on a bit by bit basis with master controlling the timing of data transmission thereby permitting a relatively imprecise timing base in the slave.

Abstract: An electronic channel selector is described for providing a tuning signal at a frequency corresponding to a selected channel. A logic circuit cooperates with an uncoded rotary switch for providing control signals to an up/down counter which counts up or down in response to rotation of a rotary switch in a clockwise or counterclockwise direction and which provides a digital signal representing a selected channel. The digital signal from the up/down counter controls a channel display and frequency synthesizer.