As you know,  the Arduino micro controller only has a USB port and a TTL UART interface, so if you need an RS232 port directly connected to your Arduino, look no further than the RS232 Shield. 

The RS232 serial port used to be the standard connection for most peripheral ports on PCs, but now the port is primarily used on industrial equipment and automation prototyping, with the RS232 Shield and its DB9 connector, you can now easily access those elements straight from your Arduino.

Documents:

• Schematics
• Datasheet (MAX232)
• Product Wiki