The Pi has a uart that is accessible on the expansion port, which we use for our wireless zigbee shield. Not too long ago I was working on a project where I wanted to see the communication between the zigbee module and the Pi. This had to do with verifying checksums for data payloads, etc.
As we all know, with windows based computers and various versions of windows (XP, Vista, 7, 8, and whatever comes next), not all versions of software programs still work. Personally, I was a huge Hyperterminal fan back in the old days. So, I was scratching for ideas of how to simply see the communication data strings that were being passed back and forth between the Pi and the Zigbee module.
Then I had one of those Aha! moments. Our serial converter tool supports the Zigbee wireless module, has the Pi interface connection, and of course, the USB connection to the computer. The Digi International X-CTU program is a free download from their website ( http://www.digi.com/support ) and once the serial protocols were set up (we typically use 9600 Buad, N81), and you go to the Terminal Page and select Show Hex, here is what you see:
Using the Serial Utility Tool and the X-CTU program, you can also see data traffic on RS485, RS232, TTl, USB and of course, the uart on the Pi traffic. This is a very simple solution to see data traffic on a serial port.
Hope you find this useful, till next time.