Default serial port parameters for the 90-30 is 19,200 baud, odd parity, 8 data bits, 1 stop bit. The programming software defaults to the same settings. Most users never need to change from the defaults.
More details about exactly what you are trying to accomplish will be helpful. Are you trying to connect to a COM port on your PC or are you using a USB/serial adapter? Are you trying to connect through the 15-pin port on the power supply? That is RS485, not RS232, so you will need a converter.