# 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

Power Gauge | Max length
--- | ---
28 | 0.81 m
26 | 1.31 m
24 | 2.08 m
22 | 3.33 m
20 | 5.00 m

## Cable colors:

Pin | Name | Cable color | Description
--- | --- | --- | ---
1 | VBUS | Red | +5 VDC
2 | D- | White | Data -
3 | D+ | Green | Data +
4 | GND | Black | Ground

Contributor: Joakim Ögren

Source:
USB FAQ at USB Implementers Forum,
USB Specification v2.0 at USB Implementers Forum

Copyright © The Hardware Book Team 1996-2001.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2001-06-06