| 摘要 |
PURPOSE:To suitably compose video information operated in accordance with the condition of presence or absence of external video information and the external video information and to select information by providing an external video information detection circuit, a synchronizing detection circuit, etc. CONSTITUTION:When the external video information comes while a system is operated under the condition without the external video signal, the information is detected by a video detection circuit 8 and the detected signal is latched to register 2. The video information from a CRT controller 4 is synchronized with the external video information by a synchronizing signal fed from a synchronizing detection circuit 7. A CPU1 reads that the contents of the register 2 is under the condition having the external video information, and instructs to compose both informations to a controller 3 and control the alternative derivation of the external video information. For this reason, a control signal is outputted to a video composite switch circuit 9 in accordance with the designation, and a composite signal of both video informations and the selected signal of the external video information is outputted. Namely, the suitable composition can be performed and the information can be selected. |
