Joel,
you still didn't tell us how you tried to read the port.

Let's say P5 is located at 0C4h (my 87C592):
P5 DATA 0C4H

To read the port just use:
mov P5,#0FFh ; activate port pullups
mov A,P5 ; P5 -> accu

or something equivalent in your high level language (C?). Not all SFRs are bitadressable, ports should be. This means that you can check or toggle single port pins as well.