Hi Dincer,

I think I've got it. I'd like to add some thoughts on how this is made up with the 8051 development system I used. Microcontroller's ~WR signal is connected directly to RAM chip's ~WR - this part wasn't so hard. (~ means pin active as 0.) However, microcontroller's ~RD (for reading from data memory, RAM) and ~PSEN (for code memory) are just ANDed, and such a signal (also active as 0) is led both to the code and data memory ~OE (Output Enable). This part isn't necessary when using Z80.

The rest of the story is simple, thanks for pointing me to. A15 address line is firstly led to the code memory directly, and to the data memory through an inverter; with the reversed double switch to the data directly, and to the code through the same (why not?) inverter.

It's very simple, thanks again :-)

All the best,
Ivan