The pins on the comm ports are hardwired to a communications chip and you do not have any choice on what functionality is available on each pin. It is possible to play games in assembly that will cause certain things to happen on pins other than either 2 or 3 (I don't remember which is the output), but it would be pretty pointless. The chip is designed to have input on 2 and output on 3 (or the reverse, if I have it backwards) and you just don't have any choice about it.

I don't know who told you you could do what you want with a comm port, but they were mis-informed.