Here is a basic computer I built using a WDC 65c02 microprocessor following Ben Eater's 6502 computer build series of videos on Youtube.
Here is a annotated version of the final build, showing how I set up the address lines and data lines.
| Address | Description |
|---|---|
| 0x0000-0x3FFF | SRAM (0100-01FF Call Stack) |
| 0x0400-0x5FFF | Reserved |
| 0x6000-0x6003 | I/O (VIA) |
| 0x6004-0x7FFF | Reserved |
| 0x8000-0xFFFF | ROM |
Although there is a decent chunk of the address space being 'unused', the trade-off is that the digital logic only uses 3 NAND gates for the entire build.