Compaq W4000 Manual De Usuario

Chapter 5  Input/Output Interfaces 

 

 
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: 

 
 

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: 
 
 
 
 
 
 
 
 

 

 
 
 
 

Desktop and configurable minitower systems only. 

P24 

 

USB 

I/F #2

 

Standard on small form factor and all Workstation units. 
Optional on Evo desktop and configurable minitower units. 

Tx/Rx Data 

Tx/Rx Data 

Front Panel 

 
 

USB Port 4

 

 

USB Port 3

 

Tx/Rx Data 

Tx/Rx Data 

Rear Panel 

 
 

USB Port 2

 

 

USB Port 1

 

 

USB 

I/F #1

 

82801 ICH2

 

 
 
 
 
 

Figure 5-7.   USB I/F, Block Diagram 

 

 

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.   
 
 
 

5-22   Compaq Evo and Workstation Personal Computers 
          Featuring the Intel Pentium 4 Processor