Take the 2-minute tour ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.

What is the extra, 5th, pin on micro usb 2.0 adapters for?


Here is an image with the different connectors. Most of them have 5 pins, but the A-type host only has four.

USB Connectors

share|improve this question
    
The image is missing/broken... –  Factor Mystic Mar 4 at 14:39

3 Answers 3

up vote 26 down vote accepted

It's for On-The-Go, to select which device is the host or slave:

The OTG cable has a micro-A plug on one side, and a micro-B plug on the other (it cannot have two plugs of the same type). OTG adds a fifth pin to the standard USB connector, called the ID-pin; the micro-A plug has the ID pin grounded, while the ID in the micro-B plug is floating. The device that has a micro-A plugged in becomes an OTG A-device, and the one that has micro-B plugged becomes a B-device. The type of the plug inserted is detected by the state of the pin ID .

OTG ID

share|improve this answer
2  
And since a Type-A connector is nearly always host it doesn't need to have a 5th pin? –  Keegan McCarthy Jul 10 '12 at 22:42
3  
If you mean a standard 4-pin Type-A plug, this would be used for a permanent host - you wouldn't use this in an OTG device. The ID pin is only used if the device can change between host and slave. For standard USB the ID pin is just left disconnected in the device. –  Oli Glaser Jul 10 '12 at 23:28
    
Yeah, that answers my question. Thanks! –  Keegan McCarthy Jul 11 '12 at 3:27

It's for host:client negotiation.

Permits distinction of host connection from slave connection

host: connected to Signal ground

slave: not connected

source

share|improve this answer
    
I'm a real newbie when it comes to serial connection. I've only just started using RS232... Can you please explain a little more? –  Keegan McCarthy Jul 10 '12 at 22:35

As shown here the original type A and B connectors use four connections, D+ and D-, which are differential data signals, along with ground and +5v. The newer mini and micro connections add an ID signal.

share|improve this answer
    
Ok, so what info does the ID signal carry? When does it use the ID pin? –  Keegan McCarthy Jul 10 '12 at 22:37

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.