Trying to enable all UARTs for writing

I have the BeagleBone Black A5A using the latest image from Angstrom.

In my uEnv.txt I have the following:
optargs=quite ddm.debug=7 capemgr.disable_partno=BB-BONELT-HDMI,BB-BONELT-HDMIN capemgr.enable_partno=BB-UART1,BB-UART2,BB-UART3,BB-UART4,BB-UART5

In my code, I open the UARTs as follows:

handle=open(info.device.c_str(),O_WRONLY|O_NONBLOCK|O_NOCTTY);

I then try to open the following:

/dev/ttyO0

/dev/ttyO1

/dev/ttyO2

/dev/ttyO3

/dev/ttyO4

/dev/ttyO5

I get an error opening /dev/ttyO3. I know it doesn’t have a RX, but I only want to send data. Is there something else I need to do to enable the UART for writing?