The universal serial bus (USB) is an external bus architecture for connecting USB-capable peripheral devices to a host computer. USB is not designed to be used as the internal bus for connecting CPUs to main memory and to devices that reside on a motherboard. Instead, USB is a communication protocol that supports serial data transfers between a host system and USB-capable peripherals. USB technology was developed as a solution to the increasing user demands on computers and the need for flexible and easy-to-use peripherals. USB technology directly affects a number of standard peripherals, such as keyboards, joysticks, mouse devices, digital cameras, computer telephony integration (CTI), and video-conferencing products.

USB offers the following benefits to system designers and users:

• USB provides a single, well-defined, standard connector type for all USB devices. This simplifies not only the design of USB devices, but also a user's task of determining which plugs correspond to which ports on their computer.
• USB eliminates the need for separate mouse, modem, keyboard, and printer ports, thus reducing hardware complexity.
• USB supports hot plugging, which means that USB devices can be safely connected and disconnected while the host is turned on. Other generic peripheral connection standards, such as the Small Computer System Interface (SCSI), require that the host be turned off when peripherals are added or removed.
• USB supports Plug and Play. When a USB device is plugged in, the host computer identifies the device and configures it by loading the appropriate driver.
• USB provides flexibility in how devices are powered. USB devices can draw power directly from the USB cable (bus-powered devices), supply their own power from batteries or from a wall outlet (self-powered devices), or use a combination of both types of power.
• USB supports power-saving suspend and resume modes.
• USB offers a high-speed 12-megabits-per-second mode (Mbps) and a low-speed 1.5-Mbps mode that support a variety of peripherals.
• USB guarantees certain amounts of bandwidth for devices that cannot tolerate transmission that comes in bursts, such as streaming audio and video devices.
• USB offers four different data transfer types that are suited to the needs of various types of peripheral.
• USB enables multiple peripherals to communicate simultaneously with the host.

  Consult the following sources for additional information about USB technology that is important both for OEMs who add USB support to their Windows CE–based platforms and for independent hardware vendors (IHVs) who build USB peripherals:

  • USB Implementers Forum Web site

    This site contains the complete USB specification, Universal Serial Bus Specification, Revision 1.1.

  • Intel Corporation Web site

    This site contains information on USB hardware and microcontroller chips, such as the 8x930Ax and 8x931xA series chips.

    Note   The official Universal Serial Bus Specification, Revision 1uses the term function to refer to USB-capable peripheral devices. However, because function typically refers to callable units of C/C++ code, Windows CE documentation uses the term USB device to refer to USB peripherals. In addition, the official Universal Serial Bus Specification, Revision 1, uses the term USB client driver to refer to device drivers for USB devices, but to avoid confusion with client/server terminology, this documentation uses the term "USB device driver."

    
    

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     Last updated on Tuesday, July 13, 2004

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