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USB Essentials

To fully appreciate the value that the ExtremeUSB® technology brings to the market, you must first understand the USB specification, its value as the defacto standard in PC and CE connectivity and its inherent limitations. This section identifies the major technical attributes of USB. For greater detail please refer to the USB Specification, which can be found at www.usb.org.

Specifications

USB technology is governed by the specifications prepared by the USB Implementers Forum (USB-IF). There have been three major revisions to this specification:

Revision 1.0, January 1996 - This version introduced all of the major components of the system.

Revision 1.1, September 1998 - This version clarified some technical issues but did not introduce any new functionality.

Revision 2.0, April 2000 - This version introduced high-speed (480 Mb/s) operation.

It should be noted that each revision of the specification is backwards compatible with previous versions. Since no functionality is deleted in later versions, all USB devices will continue to work in newer systems.

Topology

The USB system is constructed from three major subsystems:

Host Controller - This unit is mounted on a PC motherboard or PCI card. Each USB domain is managed by a single Host Controller.

Hub - This unit provides multiple attachment points to the USB.

Device - This unit provides end-user functionality. Each USB domain may contain a maximum of 127 devices USB hubs can be daisy-chained to a maximum depth of 5 units.

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