Firmware Musings 267 A typical 8-bit processor, though, is limited to 64k. Once this was an ocean of memory we could never imagine filling. Now C compilers let us reasonably produce applications far more complex than we dreamed of even a few years ago. Today the midrange embedded systems I see usually burn up something between 64k and 256k of program and data space--too much for an 8-bitter to handle without some help. If horsepower were not an issue, I'd simply toss in an 80188 and profit from the cheap 8-bit bus that runs 16-bit instructions over 1 Mb of address space. Sometimes this is simply not an option; an awful lot of us design upgrades to older systems. We're stuck with tens of thousands of lines of "legacy" code that are too expensive to change. The code forces us to continue using the same CPU. Like taxes, programs always get bigger, demanding more address space than the processor can handle. Perhaps the only solution is to add address bits. Build an external mapper using PLDs or discrete logic. The mapper's outputs go into high-order address lines on your RAM and ROM devices. Add code to remap these lines, swapping sections of program or data in and out as required.