What Is the Pin Configuration for USB Connectors?

Written by ryan k oylear
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What Is the Pin Configuration for USB Connectors?
Standard type A USB connector (Image by Fotolia.com, courtesy of amandare)

Before the mid-1990s, all you had for adding peripherals to your PC were your PS2 ports, 2 COM ports, and a parallel port. As the age of the multimedia PC came to fruition, these ports were limiting both by number, and by speed. They say necessity is the mother of invention, and USB was born out of a definite necessity.

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USB Connector Types

There are three main USB connector types: Standard USB A and B, which are used mainly on desktop PCs and also on most laptops. Mini USB A and B are still common on cellphones and smaller form factor laptops, but are being deprecated for the third connector type. Micro A and B are the newer and preferred small-device USB connectors.

USB Connector Pinouts

Each of the three types of USB connector have different shapes. They also have different pinouts. Standard USB connectors have only four pins, mini USB has five pins, but only uses four of them. Micro USB also has five pins, and makes use of either tying or not tying pin 4 to pin 5 as a means of identifying which type of connector is plugged in.

Standard USB Pinout

Looking at a standard A plug head on with pins up, the pins are numbered backwards from 4 to 1. Pin 4 is the -5 volt lead, pin 3 is the + polarity data pin, 2 is the - polarity data pin, and pin 1 is the +5 volt lead. Standard B plugs are a bit different due to shape. The plug is square, with bevels for the top corners. There are two pins on top, and two pins on bottom. The order is clockwise starting top left, 1 through 4. 1 is +5 volt lead, 2 is + polarity data, 3 is - polarity data, and 4 is -5 volt lead.

Mini USB pinout

Mini USB is simpler in layout. While the A and B plugs may be shaped different, both have five pins facing down, and in the same order, starting at 5 and counting down to 1. Pin 5 is ground, pin 4 is not used, pin 3 is data +, pin 2 is data -, and pin 1 is +5 volt lead.

Micro USB Pinout

Like mini USB, micro USB also used a five-pin connector. Unlike mini USB, the fourth pin is actually used to differentiate between an A and a B plug. The pin assignments are exactly the same as mini USB, except that for a micro A plug the fourth pin is tied to ground, and micro B the fourth pin remains unused.

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