The information seems a bit sparse but it may be using the EPL and/or SGD language that is ASCII based.
The serial port defaults to 9600,8,N,1 and is designed for connection to a PC so you will need a chip/device to convert RX/TX from UART voltage level to RS232 level and may also need it to convert DSR/CTS lines as well if it cannot be put into software flow control. I would suggest one but Maxim site is not loading for me today at work, maybe someone else can suggest one.