Matt,

Bingo! I had to believe a '138 or '139 would make more sense unless it was just labor saving to work with a '154 on a protottype board.

I built up a system a while back, and used a simple 74xx to flip the ram/rom with an I/O pin.

If this is a production design, you might still do better with a Philips XA. Its got a huge memory address space and you can drop the paging.

The bad news is that it can mean a new set of compiler/assemblers and emulators.

-Jay C. Box

The only good thing you can say for the '154 is that remarkably, its still available.