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The anatomy of USB 2.0

Well , after cutting up a firewire card it's time to look at USB 2.0. The Universal serial Bus or USB for short has been around for a while now. Originally conceived to facilitate the connection of peripherals it has been adopted by almost any computer vendor.

USB Past present and future.

The original idea was founded by a group called the CATC. or Computer Access Technology. All important computer makers were present, Dell, IBM Compaq, as well as processor and software vendors such as Intel, AMD, Microsoft. An original proposal was called the ACCES bus and loosely based on the I2C protocol. I2C is a protocol used for communication between chips. A pin for pin compatible chip was created that could replace the keyboard controller of the then common motherboards ( we are talking 386 era here ).

It soon turned out that this was impractical. However, the gained experience and know how led to the development of USB1.0. It was not until the advent of the Pentium processor and chipset's that USB started to b put on the motherboards. Pretty soon the first devices appeared.

Today a motherboard without USB does not exist. the serial ports has died all but the attachment of a modem. The printer port is doomed too. Almost all new printers come with a USB interface. The USB 1.0 was superseded by 1.1 that added a high speed mode ( 12 mbit/s iso 4mbit/s in 1.0) and added more layers in the protocol. The advent of USB cd recorders and camera's soon filled all available bandwidth available on USB1.1, and people were getting disappointed.it was time to upgrade the bus.

Version 2.0 is backward compatible with 1.0 but pushes the transfer rate to 480 Mbit./second. The first USB2.0 device were IDE controller that allowed the attachment of removable drives. Hard disk and DVD/CD recorders are readily available on this bus. The first camcorder and still camera's with USB 2.0 ar available. However only to transfer still images. Video streaming is not available ... yet.

USB technicalities:

USB is a master/slave configuration.The bus allows only for one Master. The bus arbitration is solely handled by this master without possibility for transfer of control. This is different from firewire where multiple masters can be active and pass control to each other when demand arises.

A point to point transfer is not directly possible on USB. This makes it impossible to run other protocols on top of the USB port. But then again, none of the USB device require other protocols.

usbonnect

Anatomy of a typical USB 2.0 card

Today's motherboards always feature USB 2.0 ports. But for people that simply want to upgrade their existing system there are USB 2.0 ports in the form of PCI plug in cards.

 

Image1

The above image shows such a card. Most cards are either built around an NEC controller or a VIA controller. Which controller you choose is not important as long as there are WHCL qualified drivers available for it. AWHCL driver has been tested by Microsoft and approved for use with certain OS releases.This gives a bigger chance of trouble free operation. You can search the Microsoft HCL website for certified devices.

Of course if you are not running a Microsoft operating system this is of little o no use to you.

USB cables

Well i've said it before, there is no need to buy those specially ''oxygen free copper, double isolated , extra shielded '' cables with '14 micron gold plated' connectors. It is important to have th right cable. There are currently 4 different connector types.

The most common is a A-B cable. The PC side has a A type connector

USBConnector connector  
A type plug B type plug  
     

Several hanbdheld devices feature mini plugs

male lMiniUSBJack Mini USB connectors
5pin socket Mini USB 2.0 connectors

The D-shaped connector with 'wings' is USB 2.0 compliant. THe older D connector is USB 1.1

USB hubs

If your computer needs more USB ports you can add extra cards, or you can use USB hubs.These split one port into multiple ports. There is a difference between self powered and bus powered ports. A hub that draws its power from the host has to split this power over its downstream ports. Normally a total of 500mA is available from a typical computer USB port. When given over a hub there is only 100 mA left per port.

There are hubs with more ports ( up to 7 ) and these will always be self powered. they come supplied with a power supply.

  combohub
This is a combo USB 2.0 / firewire Hub that can be instaled in a standard drive bay. since this hub is powered via an additional connector inside the PC this can deliver 500mA per port.
  usb2hub
Example of a small 4 port hub. In this case a USB 2.0 compliant hub. This hub is bus powered and thus can only deliver 100mA per port.

Conclusion

USB2.0 is here, and it's time to get it on board. Today there are plenty of devices that are compatible , either the USB 2.0 or with the older standard. It will probably take a while before we see the first video applications. After all Firewire is there the de facto standard. But for removable storage, such as DV CD and hard disks, it is great.

 


Credits

Author: Vincent Himpe ( 7 April 2003).

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