I was wondering. Rather than use code that relies on a port pin to be high then low, I was thinking of adjusting my code to something like this:

mov dph,P1
mov dpl,P1
mov A,P1
movx @dptr,A
self:
ajmp self

 

Now the above seems very ideal to me since I could write to any address, any byte, with less than 16 bytes of code.

The only question I have here is, at what points (or bytes) does the microprocessor actually read the actual port 1 data?

Does it read it when it sees P1 in the code, or does it read it between instructions?

I want to tie a NAND gate to the decoder outputs so that it returns high when P1 is not being read.