I'm trying to use a RS-232 cape in a python script. A TU-S9 USB-to-Serial converter works just fine with same code I just change the port. So I don't think it is my code. The only thing I can think of is that I am missing something setup wise. The Cape doesn't come with any documentation (that I have found). I've tried UART 1,2,4 same result. the port will open but it never gets a response from the device. The device is a DirectLogic 05 PLC. I'm using ModBus RTU.
Edit: from what I can tell the UART ports for the beaglebone are listed as /dev/ttyO0, /dev/ttyO1,/dev/ttyO2,/dev/ttyO3,/dev/ttyO4. /dev/ttyO0 is used by the OS though.