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Chapter 5 Input/Output Interfaces
5-22 Compaq iPAQ Family of Internet Devices
First Edition – March 2000
5.7 UNIVERSAL SERIAL BUS INTERFACE
The Universal Serial Bus (USB) interface provides asynchronous/isochronous data transfers of up
to 12 Mb/s with compatible peripherals such as keyboards, printers, or modems. This high-speed
interface supports hot-plugging of compatible devices, making possible system configuration
changes without powering down or even rebooting systems.
NOTE:
It is recommended to run the Windows 98 (or later) operating system when
using USB peripherals,
especially a USB keyboard and USB mouse
. Problems may be
encountered when using USB devices with a system running Windows 95, although
some peripherals (such as a modem and/or a camera) may operate satisfactorily.
As shown in Figure 5-8, the USB interface is provided by the 82801 ICH component and a USB
hub component. All models provide two front-panel accessible series-A USB ports. The legacy-
free system provides three additional series-A USB ports on the rear panel.
NOTE:
For more information on the USB interface refer to the following web site:
http://www.usb.org
Figure 5-8.
USB I/F, Block Diagram
5.7.1 USB DATA FORMATS
The USB I/F uses non-return-to-zero inverted (NRZI) encoding for data transmissions, in which
a 1 is represented by no change (between bit times) in signal level and a 0 is represented by a
change in signal level. Bit stuffing is employed prior to NRZ1 encoding so that in the event a
string of 1’s is transmitted (normally resulting in a steady signal level) a 0 is inserted after every
six consecutive 1’s to ensure adequate signal transitions in the data stream.
USB
Hub
Le
g
ac
y
-free s
y
stems onl
y
Tx/Rx Data
82801
ICH
USB
I/F
Rear Panel
USB Port 0
USB Port 1
USB Port 2
USB Port 3
Front Panel
USB Port 4
Tx/Rx Data