Compaq W4000 manual USB Data Formats, USB I/F, Block Diagram

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. More information on USB compatibility and functionality may be found at the following web site: http://www.usb.org .

As shown in Figure 5-8, the USB interface is provided by the 82801 ICH2 component. All models provide two rear-panel accessible type-A USB ports. Front panel USB ports are standard on small forma factor and all Workstation units. The Evo desktop and configurable minitower units may be upgraded to include two front panel USB ports. For more information on the USB interface refer to the following web site:

82801 ICH2

USB

I/F #1

USB

I/F #2

Tx/Rx Data

Tx/Rx Data

P24

Tx/Rx Data

Tx/Rx Data

Rear Panel

USB Port 1

USB Port 2

Front Panel

USB Port 3

USB Port 4

Standard on small form factor and all Workstation units.

Optional on Evo desktop and configurable minitower units.

Desktop and configurable minitower systems only.

Figure 5-7.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 Evo and Workstation Personal Computers

Featuring the Intel Pentium 4 Processor

Second Edition – January 2003