Why do you need a buffer? Cygnal I/O's have plenty of drive capability.

I think between what Mr. Klein and others have explained in detail, you have all the information you will need.

Now it just takes you making an effort to experiement. Why do more than you need to. If the Cygnal <--> RS232 will work just fine (as others have alluded to), then why add a buffer? That is just extra $$, extra board space, and extra debug time if something goes wrong. But if you start with the 2 chips... you will have less to debug from the beginning, especially if you are new to the whole thing.

-Rob