You don't need a max232. First thing to check is that Tx and Rx are crossed over. TX to RX and RX to TX. That would be enough to cause your problem.

Also on page 17 of the datasheet it talks about about RX input being inverted based on the TTL standard. You would need to reinvert this line for this to work properly. This can be done via software or hardware.

Let me know what you find.