8051 memory access hardware question - Home Automation

Bob F wrote:
> I have a homebuilt home control system based on an 80c51FA processor. I recently
> had a memory failure on it. It currently uses 32K x 8 bit mmemories, sharing the
> space for code and variables. I would like to replace the 2 memories with one
> 128k x 8 bit memory.
>
> It has been a long time since I did much hardware design. I am trying to figure
> out how I can connect one 128k byte memory to map to 64 KB of program and 64 KB
> of data memory, which would mean I need to select half the chip depending on
> whether I am reading program code or data. Looking at the hardware manual, I
> don't see an easy way to do this, as it seems that the RD\ or PSEN\ are normally
> used to access data or program memory, and I need a high address bit to
> differentiate them.
>
> The chip only handles a 64 KB address space. I would jumper the program memory
> to be data memory while I loaded the program, then switch the jumper back.
>
> Can anyone offer me any suggestions of how to do this? I would really like to
> increase the available space in both memories. I have one 32 pin memory socket
> and one 28 pin socket available with a fair amount of flexibility of signals to
> the high address and chip select bits.
>
>

How about RD\ | PSEN\ -> CS, PSEN\ -> high address bit?

bill

Bob F wrote:

> I have a homebuilt home control system based on an 80c51FA processor. I recently
> had a memory failure on it. It currently uses 32K x 8 bit mmemories, sharing the
> space for code and variables. I would like to replace the 2 memories with one
> 128k x 8 bit memory.

Why not have the code in ROM ? That's the norm.

Graham