Not all is what it seems!
When you look at the STK3700 there are two USB connectors.
- A Mini-B USB socket for the debug interface
- A Micro-AB USB socket the GG's USB interface.
A Mini-B USB socket is self explanatory. Details of the connector can be found at: http://katalog.we-online.com/em/datasheet/65100516121.pdf
Well what is a Micro-AB USB connector?
It is a Micro USB connector but with a different perimeter shape allowing it to function as both a Micro-A or Micro-B USB connector.
If you look carefully at this picture its perimeter shape is not chamfered but rectangular allowing both types of plug to be used.
If you think that I'm crazy here is a picture of the compatible plugs to prove otherwise.
A Micro-A USB plug on the left and a Micro-B USB plug on the right.
The Micro-AB USB connector is a part of the USB OTG (On the Go) specification.
It gives the device the ability to act as either an A or B device.
To facilitate this notice that there is an extra pin (Pin 4) this is used as a ID pin to determine whether the port is used as a Host or Peripheral.
(Connected to Signal GND = host, No Connection = slave)
When an A type plug is inserted the device defaults to its role as host and is also responsible providing power to the connected peripheral.
When a B type plug is inserted (or no plug is inserted for an OTG device) the device defaults to its role as peripheral.
The USB role can be temporarily swapped over using HNP (Host Negotiation Protocol) as needed.