I wasn't asking WHY the read-modify-write instructions read the latch and not the pin values. The reason for that was obvious to me already. Requires no explanation. What I want to know is WHICH, if not all, read-write-modify instructions do that. For the specific case in the program I'm writing, I just wanted to know if changing the source of the information to and/or/xor with the port values from A to a literal hexadecimal number made any difference.

What is this bible business? I ask an assembly language question and I'm told by not one but two responses to go read the bible? That's not the sort of response I'd anticipate.