Universal Serial Bus (USB) (technical)

Developed by Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Phillips.

Features:

• True Plug'n'Play.
• Hot plug and unplug
• Low cost
• Easy of use
• 127 physical devices
• Low cost cables and connectors

Bandwidth:

• High speed: 480 Mbps speed (in USB 2.0 and above)
• Full speed: 12 Mbps speed (requires shielded cable)
• Low speed: 1.5 Mbps speed (non-shielded cable)

Definitions:

USB Host = The computer, only one host per USB system.
USB Device = A hub or a Function.

Power usage:

Bus-powered hubs: Draw Max 100 mA at power up and 500 mA normally.
Self-powered hubs: Draw Max 100 mA, must supply 500 mA to each port.
Low power, bus-powered functions: Draw Max 100 mA.
High power, bus-powered functions: Self-powered hubs: Draw Max 100 mA, must supply 500 mA to each port.
Self-powered functions: Draw Max 100 mA.
Suspended device: Max 0.5 mA

Voltage:

• Supplied voltage by a host or a powered hub ports is between 4.75 V and 5.25 V.
• Maximum voltage drop for bus-powered hubs is 0.35 V from it's host or hub to the hubs output port.
• All hubs and functions must be able to send configuration data at 4.4 V, but only low-power functions need to be working at this voltage.
• Normal operational voltage for functions is minimum 4.75 V.

Shielding:

Shield should only be connected to Ground at the host. No device should connect Shield to Ground.

Cable:

Shielded:
Data: 28 AWG twisted
Power: 28 AWG - 20 AWG non-twisted

Non-shielded:
Data: 28 AWG non-twisted
Power: 28 AWG - 20 AWG non-twisted

Cable colors:

Copyright © The Hardware Book Team 1996-2004.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2002-01-10