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USB 1.1, 2.0, 3.0 & On-the-Go Components

  

Since its inception, USB has moved from a 12-Mbps (mega bits per second) bus to a 5-Gbps (giga bits per second) bus.  Each incremental change has been represented by a new and improved protocol, implementation, performance and compliance specification.  With each performance improvement, the USB Implementers Forum, Inc. (USB-IF) has tried to maintain backward compatibility to the previous revision level in effort to minimize detrimental impact to its installed user base.  To date, USB has seen four major improvements and its latest, USB 3.0, compares very favorably as one of the fastest buses available to the PC industry and its users.

 

         USB 1.0 ~ 12-Mbps (1996)

         USB 1.1 ~ 12-Mbps (1998) Full-Speed

         USB 2.0 ~ 480-Mbps (2000) High-Speed

         USB 3.0 ~ 5-Gbps (2008) Super-Speed

 
 
30Bandwidth
 
 

The Universal Serial Bus (USB) Specification 1.0 was officially released in early 1996 by a group of six forward-thinking companies.  This ‘Core Group’ of forward-thinking companies was comprised of Compaq, Digital Equipment, IBM, Intel, Microsoft and Northern Telecom.  Prior to the 1.0 release, the Core Group had worked closely with other concerned companies to indentify the need for a standardized ‘smart bus’ to replace the personal computer (PC) industry’s primary input/output (I/O) interfaces.  These concerned companies felt the PC industry’s aging I/O interfaces, RS-232C (Serial) and IEEE-1284 (Parallel) which had been in service for more than 25-years, were not capable of supporting their coming generations of high-performance peripheral products.     

 

Early in the evolutionary process of USB, the Core Group recognized the need to enlist support from all quarters of the PC industry to ensure USB’s successful implementation.  They formed an industry-wide non-profit special interest group, USB Implementers Forum, Inc (USB-IF).  Today, while the ‘Core Group’ has changed (Hewlett-Packard, Intel, Microsoft, NEC, ST-NXP and Texas Instruments), USB-IF continues to be a highly motivated driving force in the development, implementation and advancement of USB technology.  USB has seen several major changes since its inception.  These evolutionary changes have been based on the PC industry’s insatiable need for increased operational bandwidths and, most importantly, for improved performance characteristics.

 

Historically, USB’s performance enhancements can be traced as follows:

 

USB 1.0 ~ January 15, 1996, in its ‘root form’ featured a Low-Speed 1.5-Mbps mode for HID (human interface devices) and a Full-Speed 12-Mbps mode for of device applications.

 

 

USB 1.1 ~ September 23, 1998, improved USB’s performance characteristics that coincided with the release of Windows ‘98.

 

 

USB 2.0 ~ April 27, 2000, was again updated with the addition of High-Speed 480-Mbps mode to support the bandwidth needs of the ever evolving PC peripheral market. USB 2.0 was backward compatible with USB 1.0 and 1.1 devices.

 

 

USB 3.0 ~ November17, 2008, the PC industry’s ever increasing need for improved bandwidth capabilities saw the addition of the SuperSpeed 5-Gbps mode of operation. Once again, USB-IF placed considerable emphasis on backward compatibility to ensure installed USB 1.0, 1.1 and 2.0 devices were fully supported.

 
   

It is very important for first time designers to understand that the maximum bandwidths shown above do not represent USB’s actual ‘usable bandwidth.’  USB’s actual bandwidth will be somewhat reduced by protocol management requirements, transfer type, packet size, control transfer times, signaling overhead, et cetera.  Also, it is very important to understand that USB 3.0 5-Gbps devices require and utilize a new and unique connector interface structure requiring a fully shielded interconnect cable.  As you can see from the following cable construction and interface sketches both USB 3.0 Standard ‘A’ and Standard ‘B’ receptacles are backward compatible for use with USB 1.0, USB 1.1 and USB 2.0 peripheral devices.  To use an existing USB peripheral with a USB 3.0 ‘host system,’ the end-user simply plugs his existing USB device into the appropriate USB 3.0 style receptacle and the ‘host’ will recognize the device.  This backward compatibility feature is very important when more than 2.5-billion USB devices were sold and installed in 2008 and an equal number is forecast for 2011.

 
   
30ShieldedCable  
   
   

USB 3.0 Cable ~ Wiring Assignments

Wire #

Color

Signal

Description

1.

Red

VBUS

+5VDC (Red & Black UTP**)

2.

White

D –

USB 1.1 & 2.0 Negative Signal (Green & White UTP**)

3.

Green

D +

USB 1.1 & 2.0 Positive Signal (Green & White UTP**)

4.

Black

Power Ground

Power Ground (Red & Black UTP**)

5.

Blue

_SSRX –

USB 3.0 STP*** #1 ~ SuperSpeed Receive Negative

6.

Yellow

_SSRX +

USB 3.0 STP*** #1 ~ SuperSpeed Receive Positive

7.

BTC* Drain Wire

Signal Ground

USB 3.0 STP*** #1 ~ SuperSpeed Signal Ground

8.

Purple

_SSTX –

USB 3.0 STP*** #2 ~ SuperSpeed Transmit Negative

9.

Orange

_SSTX +

USB 3.0 STP*** #2 ~ SuperSpeed Transmit Positive

10.

BTC* Drain Wire

Signal Ground

USB 3.0 STP*** #2 ~ SuperSpeed Signal Ground

Shield/Drain

Braided Shield &

BTC* Drain Wire

Connector Shell &   Ground Plane

65% Tinned Braided Cable Shield must be in contact with the both Plug Shells.  Pigtails should terminate the BTC* Drain Wire to the device’s ground plane.

*         Bare Tinned Copper (BTC) stranded drain wire.

**       Unshielded Twisted Pair (UTP).

***      Shielded Twisted Pair (STP).

 
 

30Interface

 

   30BInterface

 

  

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