Mike:
You better be very careful with injecting don't cares. Particularly at any of the legitimate address locations within the execution range of your CrazyROM program. Any don't care you inject to 'simplify' the logic is going to end up adding 1's to the program image and end up changing the actual code that your 8051 would see to execute.

On the other hand please consider this aspect of things. If you filled all unused addresses within your CrazyROM with all d's (don't care) bits then those would group toward minimal terms in all logic product terms that you try to combine. Building a K-Map of four logic inputs A/B/C/D is an extremely easy thing to do and visualation of the mimimal groups taking the d's into account should not take more than a few minutes for each of the eight K-Maps that you would have to make.

Your minimal "program" is meant to begin right at the reset vector at address zero?? I don't see an initialize for the DPTR in your program. Is the Reset value of 0000h for DPTR correct in all cases? Is the instruction "movx @dptr,A" the sole thing it takes to induce a write cycle of your EPROM?

- mkaras