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 | USB - Overview
USB stands for Universal Serial Bus
Universal - Its a common connection between equipment
Serial - A technical term for data transmission down a single wire
Bus - A technical term meaning many devices sharing the same line
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| USB - History Some time ago the computer industry decided it needed a standard way of connecting computers to printers, scanners, cameras, mice, keyboards ... etc
They decided it needed:-
- Common cables with common connectors
- To be hot-pluggable (read more below)
- To be extendable. ie to fanout to more devices (see USB - Hubs below)
- To supply power to equipment if need be
It has been through 3 major versions (as far as we know) so far
v1.0, v1.1, v1.2 (read more about this below) |
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| USB - Hot-pluggable and Plug and Play Hot-pluggable means you can plug and unplug any USB connector at any time without damaging the equipment at either end. (disclaimer: please do consult your manuals !)
Plug and Play means that when you connect equipment to your computer, both parties introduce themselves, and do their best to set themselves up
Eg
Computer: "Hello, who are you ?"
Equipment: "Hello, I'm an Epson 680 printer"
Computer: "Do I need any drivers to work you"
Equipment: "Yes, epson_680cndjew.dll"
....
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 | USB - Cables and Connectors - Standard
Larger pieces of equipment use the standard USB cable shown
Connect to your computer (aka master/controller) using the type A connector
Connect to other equipment (slaves) using the type B connector
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 | USB - Cables and Connectors - Miniature
Smaller pieces of equipment may use a miniature B connector
There are at least 2 different types. One is shown here.
It seems to be a case of different B connectors for different manufacturers
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| USB - Versions So far as we know there are 3 major versions
v1.0
aka low speed, we think
You never really hear of this version
v1.1
aka full speed
Data transfer rate is 12 Million bits per seconds (Mbps)
This datarate is perfectly acceptable for keyboards, mice etc
v2.0
aka high speed
Data transfer rate is 480 Million bits per seconds (Mbps)
You'll only need a datarate this high for things like digicams, digital TV receivers
You can use USB v2.0 equipment on a USB v1.1 computer, but the datarate will be that of v1.1 and you may get poor results. |
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| USB - Wiring USB connectors have 4 pins
In no particular order :-
- 5 volts
- minus Data
- plus Data
- 0 volts (ground)
The 5 volts is used to power equipment from the computer's power supply
This is called bus-power
Low power equipment such as keyboards will use this 5 volts
Mains powered equipment such as printers will not
Having a minus and plus data wire serves to reduce noise (to the best of our knowledge)
If you have a lot of bus-powered equipment connected to your PC, you may get problems due to trying to draw too much current
Try disconnecting some equipment |
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 | USB - Hubs
Hubs let you convert one connection (type B) into two or more (type A)
Hubs can be connected to other hubs (see image)
Hubs can cause bottlenecks (slowing data flow)
For example if the computer, hub 2 and the USB drive are v2.0 but hub 1 is v1.1, then hub 1 will slow the USB drive to the v1.1 datarate.
'Self Powered Hubs' get their power, and power for connected equipment from a DC power supply (typically)
'Bus Powered Hubs' get their power from the computer (or in the diagram hub 1 gets it from hub 2)
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