I am unable to access expanded RAM, despite the following:
I set AUXR to 2 during startup; PSEN is tied high; all expanded RAM access is via DPTR.
Nonetheless, using my little LCD program, I can see that the one location in expanded RAM that I'm using as a counter always has the value FFFF. AUXR has the value FE.
(The program runs correctly on a Ceibo ICE using that facility's Internal RAM, but when I use its On-Chip RAM, it fails.)
It seems very unlikely that I am getting an external RAM access, because the µC writes to the LCD (3 bits of control, 8 bits of data) using the ports that external access would use for the address/data bus.
Any assistance in resolving this problem will be greatly appreciated -- thanks.