porting code from atmega644 to arduino uno/atmega328p

[peterthenovice]

 hi,

       i want to  port this code for a thermal printer controller to the uno. It is for a radio shack tp-10 thermal printer. how would i go about doing that?
       the old printer controller runs at 600 baud and uses rs232. the arduino  has a  built in usb to serial,rs232 ports are hard to find.
     

http://hackaday.com/2014/09/25/thermal-printer-brain-transplant-is-two-hacks-in-one/
https://sites.google.com/site/dannychouinard/Home/tp10upgrade

[Simon]

and ?