In order to make data communication between different manufacturers, a interfacing standard was set by EIA in 1960(i.e. RS232).The following is the pin diagram of
To communicate in asynchronous mode just three pin is sufficient. They are RXD, TXD and GND
Today RS232 is one of the widely used serial communication protocol, yet its voltage value are not compatible with TTL. In RS232 a 1 is represented by -12v and 0 is represented by +12v.So to connect RS232 with microcontroller we must connect a voltage converter such as max232 or max233 as line driver. To convert +5v of TTL logic /microcontroller to -12v and 0v to +12v we needed the line driver. This is known as Level Conversion
Usage of max233 will reduce board size (because it eliminates the capacitors) but it is too expensive than max232 .Max232 and Max233 are not pin compatible.
MAX232 IC and Atmega32 interfacing with Rs232 (db9 connecter)
MAX233 IC and Atmega32 interfacing with Rs232 (db9 connecter)