Compaq 850 manual USB Data Formats, ICH2 USB

Chapter 5 Input/Output Interfaces

5.7UNIVERSAL 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 may operate satisfactorily.

As shown in Figure 5-7, the USB interface is provided by the 82801 ICH2 component and a USB hub component. All models provide four series-A USB ports on the rear panel. For more information on the USB interface refer to the following web site:

http://www.usb.org

82801

ICH2

USB

I/F #1

USB

I/F #2

Tx/Rx Data

Tx/Rx Data

Tx/Rx Data

Tx/Rx Data

Rear Panel

USB Port A

USB Port B

USB Port C

USB Port D

Figure 5-6.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.

5-22Compaq Deskpro EXS and Workstation 300 Personal Computers

Featuring the Intel Pentium 4 Processor

First Edition – December 2000