Controller for a host device and a monitoring device connected on the basis of dvi standard

摘要

There is provided a controller that prevents any external power source from supplying its power if a host device and a monitoring device are not connected exactly through optical extension cables based on DVI standard, and that prevents a sequence for digital transmission of a video signal from being started if the external power source remains off. Only when the proper (DDC+5V) signal is generated from the host device and the external power source has been turned on, the (DDC+5V) signal is transmitted to the monitoring device, and when it is detected in the monitoring device that the transmitted signal is the proper (DDC+5V) signal, the (DDC+5V) signal is transmitted to the monitoring device. Also, when it is detected that the proper HPD signal has been generated from the monitoring device, the power of the external power source is supplied to attached circuits of the host device and the monitoring device, and if the HPD signal transmitted to the host device is the proper signal, the HPD signal is transmitted from the monitoring device to the host device.