Abstract: A USB device comprises a USB connector 1 for connecting it to a USB or HUB of a host and a serial interface engine (SIE) 2 serving as an interface. The USB connector 1 and the SIE 2 are interconnected by four signal lines defined in a USB. Of these signal lines, a 5-V power supply line for supplying 5-V power to the SIE 2 is provided with a switch 3 for electrically on-off switching it. The user can readily control the power supply from the host to the USB switch by operating the switch. Thus, when the USB device is not used, the power supply from the host can be stopped to reduce power consumption of the host.

Abstract: Predetermined ones of picture elements read from a frame memory at a first clock rate, are stored in an image memory and are read therefrom at a second clock rate for display on a display unit with the first and the second clock rates selected independently of each other. Preferably, a serial signal of the predetermined elements is converted for storage in the image memory into a parallel signal of a predetermined number of bits. The predetermined elements stored in the image memory, are read therefrom as a parallel signal of the predetermined number of bits, the read-out parallel signal being converted to a serial signal for the display.