It is very easy to control an iRobot Create with an Arduino or other microcontroller.
If you have one of the Mini-DIN cables (circular ones) that you are willing to cut up you can wire the correct pins into the TX and RX of an Arduino or PCDuino.
I have found that it is easier though to use the large DB-25 connector (which is the same one used on old printers and scanners) because it can provide 5v regulated power directly to an Arduino (but it can't provide enough current for a PCDuino) along with the serial data.
The pinouts for both of the these connectors can be found here: http://www.irobot.com/filelibrary/pdfs/hrd/create/create%20open%20interface_v2.pdf, along with a lot of other information.
For software I recommend this Arduino library: http://www.airspayce.com/mikem/arduino/Roomba/, which is simple and easy to use.
Edit: I just realized that you wanted to do this with a PCDuino, which I have never used, but I think you would have to port the library. The pdf I linked provides information on the entire protocol. If you don't need the processing power of the PCDuino it might just be easier to use an Arduino.
I hope this helps.