The power supply of microcontrollers are usially +5V or lower. This applies to all its output pins. As a result, one need to use an adaptor on the Rx and Tx pin of a microcontroller and the outside world which uses RS232 standard. The RS232 standard calls for voltages of +/- 12V to respresent logic "1" and "0".
To translate between these logic levels, one can use buffer ICs with +/- 12V power supply and is commonly done on PC motherboard as these voltage is available from the switching power supply. However, for microcontroller circuit, most often only one power supply is available and that's +5V. Therefore a special type of ICs were manufacturered that enable interfacing between the TTL and RS232 logic levels.
The MAX232 IC, requires only four small capacitors and a single power supply to perform all these translation and is very commonly used on all microcontroller projects with serial comminication to the PC.
It would be any need and indeed a waste to add one MAX232 IC to every circuit. Therefore, I think it is a good idea to build a delicated adaptor and connected it permanently on the PC serial port. Its four connections(0V,Tx,Rx and +5V) can then be applied to any microcontroller project with ease.
The adaptor has been so useful I even built one for my friend as well.
