The Universal Serial Bus (USB).

The Universal Serial Bus provides a standard data (and power) connection for everything from scanners, printers, joysticks, TV tuners, Wireless Internet, USB to Ethernet LAN and USB to Serial adaptors through to MP3 players, digital cameras, mobile phones and digital camcorders.

There are four mechanical types of connectors, these are called Type A, Type B, Mini Type A and Mini Type B connectors


Type A	Type B

Standard Type A USB Connectors

USB Type A Plug

Type A plugs always face upstream. Thus a Type A socket will generally be found on hosts and hubs, e.g. type A sockets are commonly found on PC motherboards in a desktop PC, or laptops, or USB hubs.

Standard Type B USB Connectors

Type B plugs are always connected downstream, thus type B sockets are found on USB devices such as scanners, printers etc.

Standard USB Pinouts and functions

Pin Number	Abbreviation	Function	Wire Colour
1	VCC	+5V DC	Red
2	D-	Data -	White
3	D+	Data +	Green
4	Gnd	Ground	Black

Mini Type B USB Connectors


Mini Type B Plug	Mini Type B Socket

Mini Type B plugs are a more recent development, and were introduced with USB 2.0, initially with a 4-pin version, and then with a 5-pin version 2.0 of the connector (with 1 pin unused). The 5-pin, version 2 Mini USB Type B connector is the more common of the Mini USB connectors used.

The mini Type B connectors were developed for the expanding market of miniature electronic devices such as mobile phones and personal digital assistants/organisers, because the current full size type B connector is too large to be easily integrated into small mobile devices. They have grown in popularity and are now found on many more mobile devices such as Digital Cameras, Mobile Phones, External Hard Disks, MP3 Players, Personal Video Players and Digital Camcorders. Mini Type B plugs always face upstream.

Mini Type A USB Connectors

With the extension of USB with USB on-the-go, the mini-A form factor was also defined, so that now, with the USB standard, there are 2 full size connector types, and 2 mini connector types.

The Mini Type A USB Connector has 5 pins, as with the more recent version of the Mini Type B USB Connector. In the Mini Type A Connector however, all 5 pins are used, with pin 4 being connected to pin 5, and called ID. The ID pin is used to see if a device is a host under the USB on-the-go standard.

Mini USB Pinouts & functions (Mini USB Type A & Mini USB Type B version 2)

Pin Number	Abbreviation	Function	Wire Colour
1	VCC	+5V DC	Red
2	D-	Data -	White
3	D+	Data +	Green
4	ID	ID
5	Gnd	Ground	Black

USB Technical Information

Technically, USB is a bus specification using a tiered star topology. This means that USB devices can be plugged into USB devices - in fact, up to 127 devices can be supported, as long as they are not more than 5 metres apart.

USB supports plug and play connections, and hot swappable devices (i.e. the computer does not have to be switched off to plug the device in). USB operates at 2 data rates: 12 Mbps for high bandwidth devices such as hard disk drives, and 1.5 Mbps for lower bandwidth devices such as joysticks and mice.

Comparison of USB, USB 2.0 and Serial Interfaces.

Interface	Serial	USB	USB 2.0
Speed	115 kbps	12 Mbps	20-400 Mbps
Devices connected	1	127	127

All USB devices have a connection to the host called an upstream connection. In turn, all hosts have a connection to USB devices called a downstream connection. The Upstream and downstream connectors are deliberately not mechanically interchangeable, this prevents loopback connections at a USB hub, e.g. a downstream port connected to a downstream port.