Thank you everyone for giving me so many alternatives.

To Phillip's question,

I'm asking how to interface the acia to the 8051.

I'm not sure if I can decode the 'address' as I am not using any external memory and thus according to the manual, there will not be any pins that output the address.
Thus, I thought of the inelegent method of sending (and latching) a bit to enable the acia.

Thank you.