Well the good news is that I have the source code for the PALs and the circuit diagrams for the boards. I also have one board that is running code that successfully pages through 2 megabytes of 512K flash rams.

The bad news is that I work for the company that designed the boards and they no longer employ the responsible hardware or software engineers.

I have looked at the source code in C and in assembler, and I have carefully examined timing diagrams to try to understand what was done. But I do not have the experience to recognize or understand the design.