US Patent 7274360 Multiple control system

A first controller and a second controller for controlling corresponding electronic devices, which are incorporated in a composite electronic apparatus, are connected in parallel to a display driver via a serial communication line. When the first controller controls the display driver, the first controller outputs a first control signal to the second controller so as to put a three-state output terminal of the second controller in a high impedance state. When the first controller does not control the display driver, the first controller outputs a second control signal to the second controller so as to allow the second controller to control the display driver, and puts a three-state output terminal thereof in a high impedance state.