I have a silly question. But first, I am grateful for all the work put into the memory expansion board detailed here in another thread. Thank You! I have been designing logic circuits since the RTL / ECL days, modifying motherboards and also do assembly language on multiple platforms. So I know the effort that was needed here.
Now for the silly question. Why not a static ram memory expansion that uses the ROM sockets for address & data lines? 4mb (256kx16) static ram chips are cheap. Not like in the old days when I was buying 1k x 4 2114's for $5 each.
Is it not possible to map some static memory from 128k - 512k by grabbing the address (and extra ones that are not to the ROM sockets) and R/W lines ? Like the Rominator? Static memory has like, 10ns access time vs the 450ns of the ROM and the 200ns access (335ns cycle time) of the 4864 chips. So I don't see that as a hurdle.
So please point me in the right directions so I don’t go down the rabbit hole on my next project. What am I missing?
Why do I want to do this? I have an original Mac128k board. It's been sitting around since late last century. I've added the PiPico vga adapter, my own PS/2 mouse & keyboard adapter, Floppy EMU and more. But I don't want to alter the board as there are very few untouched original 128k boards left. Yet I need more memory for System 6/7 and to play Dark Castle II.
ETA: I've written a lot of 68xxx code for Mac and was Mac / Newton Developer a long time ago.
Now for the silly question. Why not a static ram memory expansion that uses the ROM sockets for address & data lines? 4mb (256kx16) static ram chips are cheap. Not like in the old days when I was buying 1k x 4 2114's for $5 each.
Is it not possible to map some static memory from 128k - 512k by grabbing the address (and extra ones that are not to the ROM sockets) and R/W lines ? Like the Rominator? Static memory has like, 10ns access time vs the 450ns of the ROM and the 200ns access (335ns cycle time) of the 4864 chips. So I don't see that as a hurdle.
So please point me in the right directions so I don’t go down the rabbit hole on my next project. What am I missing?
Why do I want to do this? I have an original Mac128k board. It's been sitting around since late last century. I've added the PiPico vga adapter, my own PS/2 mouse & keyboard adapter, Floppy EMU and more. But I don't want to alter the board as there are very few untouched original 128k boards left. Yet I need more memory for System 6/7 and to play Dark Castle II.
ETA: I've written a lot of 68xxx code for Mac and was Mac / Newton Developer a long time ago.
