Micro dual serial controller Serial Voltages

I got a question about the serial voltage. From looking at the manual and using the transistor as a switch for the serial input with a max voltage of Vin logic. Is it safe to assume that the voltage of the serial input is from 2.5v to 5.5v? The reason I ask is because the manual makes references to the TTL levels which I believe there are two different standards one being at 3.3v volts and another being 5v.

Does the logic voltage have to be at the same as serial voltage? For example will damage occur if logic voltage is 3.3v and serial voltage is 5v?

The other question I have is that the manual I have and the online manual are different in terms of how pins are shorted together. Pins 6-4 and 7-8 are joined together on the DB 9 serial cable (I’m hooking this up to a pc), where in the printed manual I have pins 6-7 are hooked up. Which way is right?

Thanks in Advance,