Conventionally, as disclosed in Patent Literature 1, an on-board electronic device having CPUs and substrates, respectively corresponding to types of functions, such as a navigation board on which a CPU to perform navigation processing is mounted and an audio board on which a CPU to perform audio processing is mounted, is known. Note that this type of on-board electronic device is often integrated with a display and a touch panel.
Further, in recent years, in accordance with multimedization in the vehicle, a configuration, where a user interface unit (UI unit) having integrated display and touch panel is connected to a plurality of electronic devices mounted on the vehicle such as a navigational device and an audio instrument, via a display control unit (hereinbelow, DCU), is increasingly adopted. The DCU plays a role in control of the respective operations of the plurality of electronic devices connected to the own device, and generation (or acquisition) of image data to be displayed on the display based on requests from the respective electronic devices, and display of the image data on the display. Hereinbelow, a unit where the UI unit and the DCU are integrated will be referred to as a display unit for vehicle.
A conventional DCU has two substrates, i.e., a main board mounted with a main CPU and a sub board mounted with a sub CPU and a power supply circuit. The main CPU mainly controls the operations of the electronic devices connected to the own device, and draws an image to be outputted to the display. The sub CPU performs management (acquisition and storage) of vehicle information inputted from an in-vehicle network, and controls electric power supply to the respective elements of the display unit for vehicle in cooperation with the power supply circuit.
The conventional DCU has two substrates, i.e. the main board and the sub board, mainly for reducing the area of each substrate to an area smaller than that of the display.
More particularly, to realize a function, performed with a main board and a sub board, using one substrate, the area of the substrate is larger than the area of the display. When the area of the substrate is larger than the area of the display, its housing is also larger than the display, to impair mountability to the vehicle.
Accordingly, in the conventional DCU, a function to be provided in the DCU is shared with the two substrates, the main board and the sub board, so that the size of each substrate is suppressed to be equal to or smaller than the size of the display.
However, in the conventional display unit for vehicle (more particularly, DCU) having two substrates, the manufacturing cost such as costs of parts and machining cost is increased. The machining cost here includes costs necessary for assembling work of the respective substrates in the housing and wiring connection work between the substrates.
Further, it is desired to increase the CPU clock for improvement in DCU performance. However, in the conventional DCU, the space in the housing is partitioned with the two substrates. When the clock is increased, radiation with a cooling fan becomes insufficient. Accordingly, from the viewpoints of manufacturing cost and heat dissipation, it is preferable that the number of the substrates is one.
On the other hand, as described above, when a function realized with two substrates is simply integrated in one substrate, the area of the substrate becomes larger than the area of the display, which might impair the mountability. Especially, when the difference between the area of the display and the area of the substrate is large, i.e., when the area of the substrate is larger, the mountability is impaired.