The two types of interfaces are not directly compatble. Quote: "RS485 interface gives some more benefits compared to RS232: simplicity and the robustness for long distance transfer. RS485 is simpler because it uses only two ire (or a single pair) to carry out the data in bidirectional manner, using RS232, we need 3 wires at minimum to carry the data bidirectionally. RS485 cable length can be as long as 1.2 km, while RS232 only about 25 meters."
There are many circuits available and on this forum, too! Search the forum for "rs232 rs485 converter" and see if you can find what you need.