KaiDaniel wrote:


> Hello,


> regarding the expansion board "summit" for the Overo GumStix I have

> got a

> question: Where can I find a serial port connector (RS232/UART)?


> 2x 2-wire serial ports are announced at:

> http://www.gumstix.com/store/catalog/product_info.php?cPath=31&product

> s_id=215


> The 40-pin header is described under:

> http://www.gumstix.net/Hardware/view/Hardware/Summit-board-40-pin-head

> er/112.html


> But there is no further explanation. So I like to know, if there are a

> pins for a serial communication according to RS232/UART protocol.


> Thank you in advance for answering.


> BR,

> Kai



I have just been going through this exercise myself, and here is what I've found:


Information on using Overo serial ports:


Connections for the serial ports on the Overo are available on the 40-pin Summit board header:


They are:

UART 1 (/dev/ttyS0): pins 9 and 10 (these are connected to pins 24 and 48 of the 70-pin J4 connector)

UART 3 (/dev/ttyS2): pins 21 and 22 (these are connected to pins 26 and 31 of the 70-pin J1 connector)


For reference, the 70-pin J1 and J4 connector pin-outs are available at:



There is also a third serial port available (UART 2, /dev/ttyS1), but it is slated for use with Bluetooth.  The first Nabble posting URL I include below discusses a workaround that shows how to use this third serial port.


A couple good postings about using serial on Overo:




A couple sections from this second Nabble posting are listed here for reference:




Using the UART is as simple as it is in any other Linux distro - simply open /dev/ttyS0.  If you don't know how, Google it - there are several Linux serial port how-to's that do a great job of describing it.  The two wire ports, while I'm not sure exactly what byte order, format etc it's expecting things in, can be found at /dev/i2c-1.  You should be able to access GPIO through devices in the /sys/class/gpio folder.


Make sure you level shift from 1.8V logic - I've found Sparkfun's logic level converters to be invaluable for prototyping:



Hope this helps - I'm really not too much further than you are.  While I'll second the lamentation that the documentation is virtually non-existent, I've used other Linux boards and the learning process is much the same.  You have to expect this when diving into the embedded Linux world!




One thing you must realize is that everything on a linux system becomes a file , just have a look in /dev/ Once someone has written a driver for a device is usually shows up on /dev/(SOMEPATH).

You can look at some of the older i2c-io code that reads and writes to the i2c bus, very strait forward.

Quick and dirty way to get to things

f = open("/dev/blah","r") ;



I ended up doing this for a honeywell compass . I had to have two file hands one for writing and one for reading.




Since Overo uses 1.8V logic, a voltage level translator will be required for many applications.  Two such units that I saw referenced are:

TI’s TXB0104




Sparkfun’s Logic Level Converter (referenced in the second Nabble URL above,