USB 2.0 Specification

This chapter provides the mechanical and electrical specifications for the cables, connectors, and cable assemblies used to interconnect USB devices. The specification includes the dimensions, materials, electrical, and reliability requirements. This chapter documents minimum requirements for the external USB interconnect. Substitute material may be used as long as it meets these minimums.
6.1 Architectural Overview
The USB physical topology consists of connecting the downstream hub port to the upstream port of anotherhub or to a device. The USB can operate at three speeds. High-speed (480 Mb/s) and full-speed (12 Mb/s)require the use of a shielded cable with two power conductors and twisted pair signal conductors. Lowspeed
(1.5 Mb/s) recommends, but does not require the use of a cable with twisted pair signal conductors.The connectors are designed to be hot plugged. The USB Icon on the plugs provides tactile feedback making it easy to obtain proper orientation.
6.2 Keyed Connector Protocol
To minimize end user termination problems, USB uses a “keyed connector” protocol. The physical difference in the Series “A” and “B” (or “mini-B”) connectors insures proper end user connectivity. The“A” connector is the principle means of connecting USB devices directly to a host or to the downstream port of a hub. All USB devices must have the standard Series “A” connector specified in this chapter. The “B” (or “mini-B”) “B” connector allows device vendors to provide a standard detachable cable. This facilitates end user cable replacement. Figure 6-1Figure 6-1 illustrates the keyed connector protocol.