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Encyclopedia > USB Human Interface Device class

The USB human interface device class ("USB HID class") is a USB device class that describes human interface devices such as computer keyboards, computer mice, game controllers, and alphanumeric display devices. The USB HID class is defined in a number of documents provided by the USB Implementers Forum's Device Working Group. The primary document used to describe the USB HID class is the Device Class Definition for HID 1.11. There are a number of other documents that describe more specific devices in the HID class. Note: USB may also mean upper sideband in radio. ... Type A USB connector Dual images of the two Type B USB connectors, mini and full size, side and front view, compared with a U.S. 5¢ piece (nickel) in both images for scale. ... A human interface device or HID is a type of computer device that interacts directly with and takes input from humans, such as the computer keyboard, computer mouse, joystick, graphics tablet, and the like. ... A computer keyboard is a peripheral modeled after the typewriter keyboard. ... Operating a mechanical 1: Pulling the mouse turns the ball. ... A game controller is an input device used to control a video game. ... A display device is a device for visual or tactile presentation of images (including text) acquired, stored, or transmitted in various forms. ... The USB Implementers Forum USBIF, is the organisation which defines the Universal Serial Bus (USB) standard. ...

Contents


Devices

The USB HID class describes devices used with nearly every modern computer. Many predefined functions exist in the USB HID class. These functions allow hardware manufacturers to design a product to USB HID class specifications and expect it to work with any software that also meets these specifications.


Keyboards

Keyboards are some of the most popular USB HID class devices. The USB HID class keyboard has replaced the PS/2 keyboard on most modern computer systems. The USB HID class keyboard is normally designed with an IN endpoint that communicates keystrokes to the computer and an OUT endpoint that communicates the status of the keyboard's LEDs from the computer to the keyboard. The PC 97 standard requires that a computer's BIOS must detect and work with USB HID class keyboards that are designed to be used during the boot process. The Personal System/2 or PS/2 was IBMs second generation of personal computers. ... The PC 97 standard is a set of design requirements developed by Microsoft and aimed at making PCs easier to use by maximizing cooperation between the operating system and hardware. ... Phoenix AwardBIOS on a standard PC BIOS, in computing, stands for Basic Input/Output System or Basic Integrated Operating System. ...


Mice

Computer mice are equally popular USB HID class devices. Much like keyboards, USB HID class mice have replaced PS/2 mice on many modern computer systems. USB HID mice can range from single-button simple devices to multi-button compound devices. Most modern operating systems ship with drivers for standard HID mice designs; mice with extended functionality require custom drivers from the manufacturer. The Personal System/2 or PS/2 was IBMs second generation of personal computers. ...


Game controllers

Modern game controllers and joysticks are often USB HID class devices. Unlike legacy game port devices, USB HID class game devices do not normally require proprietary drivers to function. Nearly all game devices will function using onboard drivers as long as the device is designed around the drivers and the USB HID class specifications. For other uses, see Joystick (disambiguation). ... The game port is the traditional connection for video game input devices on an x86-based PCs. ...


Other devices

The USB HID class specifications allow for a myriad of other devices under the USB HID class. Some examples are automobile simulation controllers, exercise machines, telephony devices, audio controls, and medical instrumentation. Any device can be a USB HID class device as long as a designer meets the USB HID class logical specifications. This is not to say that there is no need to ship drivers for these devices, nor that an operating system will immediately recognize the device. This only means that the device can declare itself under the human interface device class. In telecommunication, Telephony encompasses the general use of equipment to provide voice communication over distances. ...


Drivers

One of the benefits of a well-defined specification like the USB HID class is the abundance of device drivers available in most modern operating systems. The USB HID class devices and their basic functions are defined in USB-IF documentation without any specific software in mind. Because of these generic descriptions, it is easy for operating system designers to include functioning drivers for devices such as keyboards, mice, and other generic human interface devices. The inclusion of these generic drivers allows for faster deployment of devices and easier installation by end-users. A device driver, often called a driver for short, is a computer program that enables another program, typically an operating system (OS), to interact with a hardware device. ...


Logical specifications

Functional Characteristics

The USB human interface device class can be used to describe both device and interface classes. The interface class is used when a USB device can contain more than one function. It is possible, therefore, to have USB devices with two different interfaces at the same time (e.g. a USB telephone may use a HID keypad and an audio speaker.)


The interface devices are also defined with subclass descriptors. The subclass descriptor is used to declare a device bootable. A bootable device meets a minimum adherence to a basic protocol and will be recognized by a computer BIOS.


Each USB HID interface communicates with the host using either a control pipe or an interrupt pipe. Isochronous and bulk pipes are not used in HID class devices. Both IN and OUT control transfers are required for enumeration; only an IN interrupt transfer is required for HID reports. OUT interrupt transfers are optional in HID class devices.


Reports

It is impossible to accurately predict and define all current and future human interface devices. Because of this, the USB HID class requires that every device describes how it will communicate with the host device. During enumeration the device describes how its reports are to be structured so that the host device can properly prepare to receive this information.


The host periodically polls the device's interrupt IN endpoint during operation. When the device has data to send it forms a report and sends it as a reply to the poll token. Common devices such as keyboards and mice send reports that are well-defined by manufacturers such as Microsoft. When a vendor makes a custom USB HID class device, the reports formed by the device need only match the report description given during enumeration and the driver installed on the host system. In this way it is possible for the USB HID class to be extremely flexible.


External links

  • USB.org - The homepage of the USB Implementers Forum, Inc.
  • Microsoft Related HID Documentation - The USB-IF's collection of Microsoft's HID documentation.
  • USB-IF HID Tools - The USB-IF's page devoted to human interface devices. Includes all approved documentation.
  • Lakeview Research HID Page - A collection of articles about, and example code for USB HID devices.
  • PC System Guides - Microsoft's PC System specifications (e.g. PC '97, PC '98).

 
 

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