In recent years, a portable device which can display a video with high definition such as a smartphone and a tablet has been widely used. Accordingly, development in the MHL which is a communication interface standard to transmit a video at high speed for the portable device has been proceeded (for example, refer to Patent Document 1).
As a communication interface standard for realizing uncompressed digital video transmission, the high definition multimedia interface (HDMI®) (registered trademark) is exemplified. Whereas, main characteristics of the MHL is to minimize a mounting area as a minimum pin configuration necessary for video transmission and to assist power supply.
The MHL devices are classified into three categories, i.e., a source device for transmitting a video signal, a sink device for receiving and displaying the video signal, and a dongle device for converting the video signal in the MHL format into the other video signal. Then, an MHL cable which satisfies the MHL standard is used to connect the MHL devices and to transmit signals between the MHL devices. The source device includes a personal computer, a smartphone, a tablet terminal, a game machine, and a digital camera. Also, the sink device includes a display device such as a digital TV. A single MHL cable connects the source device to the sink device so that a video with high definition can be transmitted and power can be supplied (charge the source device).
In a communication system according to the MHL standard, basically, regular power supply is started after a link is established between the source device and the sink device. Therefore, when the MHL cable used to connect between the source device and the sink device is an active cable and when the source device (Direct Attached Device) is directly connected to the sink device without using the MHL cable, there is a problem in that a failure such that start-up is not available due to short power supply at the time of start-up is caused or that it is necessary to have an external power supply.