given p1.0, i may write a 1 to it so that "p1.0 pin" becomes high. if "p1.0 pin" is held low by an external signal (although i have written a 1 on it), i would read p1.0 now (from the code) as 0.

is that right?
With a question like this you obviously have no idea about how the '51 works. READ "THE BIBLE" or you will have another question in 5 minutes. If you do not understand this you may end up popping chips.

BTW the answer is yes

Erik