Shahzad,

You have got the answer, the chip is MAX232/MAX232C (although there are 100's of other). The C partnumber requires four 100 nF capacitors. It is cheap and easily availabale. Look at the data sheet for how to use it.

You can also make your own converter, its easy.


TTL RS-232
+5V ----> -12 V
0V -----> +12 V

So you can make your own converter/level shifter, but its wise to use a ready made product.

Using resistors is not advisable in any case.

Regards

IA