Abstract: A method and device are provided for activating certain functions of a powered-off device having a serial data bus interface when it is attached to a powered device via the serial bus interface. On detection of a voltage on the power line of the serial bus, the processor of the device is booted in a special operation mode, wherein certain functions of the serial data bus interface can be used without powering the complete device. The device may then be enumerated by the attached host device and for example allow access to its memory unit or use the power signal on the serial bus interface for battery charging.

Abstract: A method and device are provided for activating certain functions of a powered-off device having a serial data bus interface when it is attached to a powered device via the serial bus interface. On detection of a voltage on the power line of the serial bus, the processor of the device is booted in a special operation mode, wherein certain functions of the serial data bus interface can be used without powering the complete device. The device may then be enumerated by the attached host device and for example allow access to its memory unit or use the power signal on the serial bus interface for battery charging.

Abstract: A method and apparatus are disclosed for connecting USB devices in a USB connection to save power and enable role changes between the USB devices in a USB-OTG connection, while the USB devices are in an active state wherein an A-Device informs a B-device, that the A-Device will lower the Vbus-signal to a lower voltage level (e.g. 3.3V), provided the A-Device has recognized that the B-Device supports SRP and HNP. The lowered voltage level enables the A-Device to save the power. The lowered Vbus level now allows the B-Device to raise the Vbus voltage to 5V, which is detected on the A-Device. Whenever the A-Device recognizes, that the B-device has raised Vbus to 5V, the A device interprets this as a request of the B-device to gain the host role. The A-Device suspends the USB-Bus at the earliest possible time to allow the B-Device to perform HNP, and assume the role as host.