UEXT is a board to board connector which supports three serial communication interfaces I2C, SPI and UART. It is a great way to add features to the development boards so customer can choose which feature he wants to expand.
Back in the year 2000 we started to design different development boards. There were many features which we wanted to implement to all boards like wireless communication, relay output, optoisolated inputs, audio, RS485, etc, but we realized that not all customers will need all of these features at once - why put all of this on every board and make the customer pay for all of the features but use only a few? For instance, one customer will need Zigbee, while another one will need Bluetooth, so we asked ourself how to develop our boards so that everyone is happy without making the boards unnecessarily expensive?
Then we started thinking about some kind of universal connector for which we would know which pin is connected to where. With it we would be able to develop different expanding modules and be able to connect other boards via it as well.
Every decent microcontroller has RS232, SPI and I2C - these are the basic interfaces and they give quite enough freedom to develop different modules.
This is how UEXT (Universal-EXTension-Connector) was born. We started including it in each OLIMEX board designed after 2004.
To summarize: UEXT is a board to board connector which supports three serial communication interfaces - I2C, SPI and RS232. It is a great way to expand the features of the development boards. The customer can choose which feature he wants to use.