This is sparkfun breakout module for the must have RS232 –TTL converter IC. This is the RS232 converter IC that is capable of running at 3V and communicating with 5V logic. All the necessary pins are made available through pin headers and required capacitors were added.

Remember that because the MAX3232 operates at a broader voltage range than the 232 (3 - 5.5V) you can use this on both your 3.3 and 5V projects.

 RS3232 Datasheet.