This is where I left off the other night, I am re-using some perf board from another project. I still need to remove the rest of the clock circuit, RAM, and ROM that is left over from a homebrew 6502 computer. the card edge connection was salvaged from a bad AT&T Merlin system phone card.
This is the very simple schematic for the expansion card. A quad 2-input AND gate, quad 2-input OR gate, dual 2-4 de-multiplexer, and 8 bit bus transceiver are used.
Memory map showing the address bits that can be used for decoding the memory mapped to the card, as well as the on-board memory limits and the start of UMA.