Yes Erik, I am using an actual 8751H and an 8155. I use Intel's original assembler too. You pros must be having a good laugh just about now! I'm using the 8155 mostly for the extra I/O ports but the RAM could come in handy. By connecting the M/IO line to P2.0, the ports become memory mapped at addresses 101, 102 and 103 hex.
Now visualize that P2.0 is pulled to ground (or Vcc) by a switch, how in the world is the memory mapping going to work.

You can, of course, read the switches before any external RAM acces, turn on a led and loop till all switches are off.

Erik