Using the USB OTG present on the DECA MAX10 board

The OTG port cannot be used for RS232 without lots of software support.

If you just need to see printf output for debugging, add a JTAG UART to your system. The debugger can show you printf output, but the system won't run without the debugger running.

I if you need an RS232 that operates independently, you use a regular UART. Get a 3.3 volt compatible Rs232 to USB adapter. In the US, they are available from Adafruit, Sparkfun, element-14, and others. You then wire it to some pins on the expansion connector, you will need TX, RX, and ground. Use the pin planner to set 3.3 volt logic, and define the pins being used. Don't forget to configure the pin wired to TX on the adapter as RX on th FPGA and the pin wired to RX on the adapter to TX on the FPGA.