A system based on 8031 has a von Neumann architecture. It contains 8K EPROM and 16K RAM (this one I recently used had a PPI too, but it was always at address which didn't overlap neither with code nor with data memory).

Initially, when a switch is "up" (first position), EPROM begins at 0000h and RAM begins at 8000h; when the switch is reversed ("down") starting addresses of EPROM and RAM are swapped. I'd like to know how is this achieved, that is what logic is used and which CPU pins are connected to.

Best wishes,
Ivan

P. S. The idea is to use monitor program in code memory after power-up to place program in RAM, and then after reversing the switch and resetting (simultaneously, if possible) to start program in RAM at 0000h.