using rs232 on due

I am attempting to send messages over rs 232 to some motors. i have a rs 232 shield that i was able to connect to an uno and make it work the way i expect it to. i now need it to run on a due because i am using an udoo.

i have tried hooking a level converter and that seemed not to work. i am not sure what to do. the only thing that is suspicious to me is that when i program for the udoo i use softwareserial.h and on the due the library is not available. i was going to try to install the library but i believe there is 3 serial ports available on the due. thanks for your help