USB and IEEE 1394

USB

USB is a serial interface technology intended to replace existing serial and parallel ports. The advantages of USB technology are increased interface speed, full Plug and Play support, and the ability to create a network of serial devices off a single serial port.

USB is a cable bus that supports data exchange between a host computer and a range of simultaneously accessible peripherals. The attached peripherals share USB bandwidth through a host-scheduled, token-based protocol. The bus allows peripherals to be attached, configured, used, and detached while the host and other peripherals are operating. This ability is referred to as dynamic (or hot) attachment and removal. USB is a low cost, simple, powerful solution to the input/output (I/O) problem.

Understanding USB Versions

Windows XP originally released with support for USB 1.1 controllers and devices. These devices supported low-speed and full-speed operation at 1.5 and 12 Mbps, respectively.

USB 2.0 provides support for the above two speeds, as well as for high-speed operation at 480 Mbps. Because USB 2.0 supports all these transfer rates, USB 2.0 is not the same as high-speed USB. only devices with the USB 2.0 Hi-speed logo support the 480 Mbps rate.

Limitations: The following limitations exist with USB and should be considered when troubleshooting issues with USB devices:

Bus-powered hubs cannot be plugged into other bus-powered hubs. A bus-powered hub is one which does not have its own power source.

Devices requiring a large amount of bus power cannot be plugged into bus-powered hubs.

Cable segment lengths between any device, hub, or host controller is limited to no more than 5 meters.

The USB 1.1 specification limits the number of simultaneously connected devices to 127. Several self-powered hubs connected to each of the root hubs may be required to get this number of devices.

Troubleshooting USB

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