USB Universal Serial Bus Connectors, Pinouts & Cables

- USB, the Universal Serial Bus has a number of connector and cable options each with simple and standard connections / pinouts.

USB-Universal Serial Bus tutorial includes:
    •  USB introduction
    •  USB standards
    •  Connectors, pinouts & cables
    •  Data transfer & protocol

The USB connector is remarkably simple having just four main connections for the data and power.
In addition to this it is also possible to use extender cables.
The maximum allowable length for an individual cable is 5 metres (3 metres for slow devices) and this allows the USB data acquisition module to be located remotely from the computer.
Like all connectors, those used for USB have male and female versions to ensure that devices are mated in the correct direction.

Typical USB connector

Remote devices have what is termed an upstream connection to a host. In turn hosts have downstream connections to remote devices.

Upstream and downstream connectors are not mechanically interchangeable. This ensures that they can only be connected in the required direction, thereby eliminating the possibility of issues such as illegal loopback connections at hubs like downstream ports being connected to another downstream port.

Until recently there was no peer-to-peer functionality.

USB connector types

As the concept of USB has developed, so too have the connectors. Data transfer speeds have risen, and the requirement for smaller connectors has increased.

As a result there are seven USB connector types: Type A, Type B, Mini-A, Mini-B, Micro-A,Micro-B and Micro-AB. Types A and B have 4 pins within the connector, Mini and Micro A and B connectors have five pins.

 USB type A connector outlines

A USB cable can have one of two forms of connector in the original system. These are designated the "A" and "B" connectors. The connections to the connectors are given below:

Type A USB connector pinout

The USB Type A plug is the male version of the connector. What might be referred to as the socket, is the female connector or receptacle, although it is often referred to as the port.

The female connector or receptacle is the type found on the host, e.g. computer, etc, whereas the male will be seen on items like flash memories, mouse connector, keyboard connector, etc..

There is some colour coding on these connectors in terms of their capabilities. USB 3.0 Type A connectors are often, but not always, the coloured blue. USB 2.0 Type A and USB 1.1 Type A connectors are often black, but this is not always the case. 

USB type B connector outlines

A second connector type known as the Type B was often used for smaller peripherals. This had slightly different pinout arrangement.

Type B USB connector pinout

USB Type A & B pinouts / connections
The basic USB pinouts for the connectors are given in the table below. Apart from the USB connector pinouts, the table also gives the wire colours used within the cables.

TYPE A & B USB CONNECTOR PIN ASSIGNMENTS
PIN	WIRE COLOUR	SIGNAL NAMES
1	Red	Vbus 4.75 - 5.25 V
2	White	Data -
3	Green	Data +
4	Black	Ground
Shell	Drain wire	Shield

The connectors used for USB are designed to enable the power and ground connections to be made first applying power to the device before the signal lines are connected. This prevents the possibility of the signal lines being connected first with the possibility of power being drawn through them that could cause damage to the device.

USB mini connector

With the reduction in size of many items of electronic equipment, even the Type-B connector was too large. As a result a USB Mini connector was devised and this is used on many cameras and mobile phones where space is at a premium. Two versions are available, namely the USB mini-A and the USB Mini-B.

These USB mini connectors, both the Mini-A and Mini-B provide very compact connectivity, while also being able to provide a robust connector solution. The Mini-A and Mini-B plugs are approximately 3 by 7 mm

USB micro connector

With space being even more confined on may items like today's modern cellphones, an even smaller connector solution was needed and accordingly developed.

Known as the USB micro connector, again both USB Micro-A and USB Micro-B versions are available.

The Micro-USB plugs have a similar width and approximately half the thickness of their Mini-USB counterparts. This enables them to be used in much thinner items of electronic equipment.

The micro-A connector is 6.85 by 1.8 mm and it has a maximum over-mold size of 11.7 by 8.5 mm. The micro-B connector is 6.85 by 1.8 mm and this one has a maximum over-mold size of 10.6 by 8.5 mm.

There is also a Micro-AB receptacle (socket) that can mate with both USB Micro-A and USB Micro-B plugs.

The USB Micro connector has been adopted by many organisations as a standard. The Open Mobile Terminal Platform, OMTP, endorsed Micro-USB as the standard connector for data and power on mobile device. Also the International Telecommunication Union, ITU, announced that it had embraced micro-USB for its Universal Charging Solution, thereby enabling chargers to all use the same connector and allowing standardisation and for one charger to be used for multiple types of equipment, e.g. phones from different manufacturers, etc..

Mini and Micro USB connector pinouts / connections

MINI & MICRO USB CONNECTOR PIN ASSIGNMENTS
PIN	WIRE COLOUR	SIGNAL NAMES
1	Red	Vbus 4.75 - 5.25 V
2	White	Data -
3	Green	Data +
4		Not connected, although it can sometimes be ground or used as a presence indicator.
5	Black	Ground
Shell	Drain wire	Shield

By Ian Poole