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USB in a Nutshell - Making Sense of the USB Standard

Starting out new with USB can be quite daunting. With the USB 2.0 specification at 650 pages one could easily be put off just by the sheer size of the standard. This is only the beginning of a long list of associated standards for USB. There are USB Class Standards such as the HID Class Specification which details the common operation of devices (keyboards, mice etc) falling under the HID (Human Interface Devices) Class - only another 97 pages. | USB in a Nutshell. Making Sense of the USB Standard. Starting out new with USB can be quite daunting. With the USB 2.0 specification at 650 pages one could easily be put off just by the sheer size of the standard. This is only the beginning of a long list of associated standards for USB. There are USB Class Standards such as the HID Class Specification which details the common operation of devices keyboards mice etc falling under the HID Human Interface Devices Class - only another 97 pages. If you are designing a USB Host then you have three Host Controller Interface Standards to choose from. None of these are detailed in the USB 2.0 Spec. The good news is you don t even need to bother reading the entire USB standard. Some chapters were churned out by marketing others aimed at the lower link layer normally taken care off by your USB controller IC and a couple aimed at host and hub developers. Lets take a little journey through the various chapters of the USB 2.0 specification and briefly introduce the key points. Chapter Name Description Pages 1 Introduction Includes the motivation and scope for USB. The most important piece of information in this chapter is to make reference to the Universal Serial Bus Device Class Specifications. No need reading this chapter. 2 2 Terms and Abbreviations This chapter is self-explanatory and a necessary evil to any standard. 8 3 Background Specifies the goals of USB which are Plug n Play and simplicity to the end user not developer . Introduces Low Full and High Speed ranges with a feature list straight from marketing. No need reading this chapter either. 4 4 Architectural Overview This is where you can start reading. This chapter provides a basic overview of a USB system including topology data rates data flow types basic electrical specs etc. 10 5 USB Data Flow Model This chapter starts to talk about how data flows on a Universal Serial Bus. It introduces terms such as endpoints and pipes then spends most of the chapter on each