First, I think it would be a lot easier if you chose a PIC with a real RS-232 port, but -

one way would be to set up a 416uSec interrupt, (one half bit time at 1200 baud) and then use a slight variation of one of the assembly bit-banging routines. An example can be found at

http://www.winpicprog.co.uk/pic_tutorial7.htm


The big problem is catching the first negative-going transition of the START bit on receive. You will need to connect the RxD line to a pin that has an
interrupt-on-change function.