Introduction
Like a well designed automobile or appliance, a USB peripheral’s outward simplicity hides internal complexity. There’s a lot going on “under the hood” of a USB device, which gives the user a new level of convenience. For example:

• A USB device can be plugged in anytime, even when the PC is turned on.
• When the PC detects that a USB device has been plugged in, it automatically interrogates the device to learn its capabilities and requirements. From this information, the PC automatically loads the device’s driver into the operating system. When the device is unplugged, the operating system automatically logs it off and unloads its driver.
• USB devices do not use DIP switches, jumpers, or configuration programs. There is never an IRQ, DMA, MEMORY, or IO conflict with a USB device.
• USB expansion hubs make the bus available to dozens of devices.
• USB is fast enough for printers, CD-quality audio, and scanners.

USB is defined in the Universal Serial Bus Specification Version 1.1 (//usb.org), a 268-page document that describes all aspects of a USB device in elaborate detail. This EZ-USB Technical Reference Manual describes the EZ-USB chip along with USB topics that should provide help in understanding the Specification