Abstract: A communication system for e.g. an automobile including a system control unit for activating a selected audio/video device (such as an AM/FM tuner or a navigation system) in response to a request signal transmitted on a bus from a command input terminal. The system control unit generates command signals necessary to activate the selected audio/video device in response to the request signal, including command signals to de-activate any currently-operating devices. Conversely, adjustment commands (such as volume change or channel change commands) are transmitted directly (that is, unchanged by the system control unit) from the command input terminal to the selected audio/video device on the first bus line. In addition, the audio/video devices transmit reset signals whenever power is shut-off and then restored. Each reset signal includes a transmission source address corresponding to the audio/video device which transmitted the signal.

Abstract: A radio receiver includes a first tuner, a first intermediate-frequency amplifier, at least two intermediate-frequency filters connected between the first tuner and the first intermediate-frequency amplifier and having difference frequency bands, a switching circuit for applying an output signal from the first tuner through a selected one of the intermediate-frequency filters to the first intermediate-frequency amplifier, an automatic gain control circuit for controlling the gain of the first tuner, a first phase-locked loop for enabling a local oscillator in the first tuner to oscillate at a frequency dependent on the frequency of a desired channel, a second tuner, a level detector circuit for detecting the level of an output signal from the second tuner, a second phase-locked loop for enabling a local oscillator in the second tuner to oscillate at a prescribed frequency, and a controller for controlling the first phase-locked loop to enable the first tuner to receive and issue a desired signal from a desire