6502.org

Hello all... I've got yet another question for ya'll. Most computers (Pentium class and up) that I have access to use Flashable type memory chips as the bios. Can this be used in a 6502 computer? And if so, what is the upper limit (ie., max amount of memory)? Can I use a 1MB chip? Could I use one with more memory? Any info/help would be appreiciated.
Thanks.
Lyos Gemini Norezel

> Can this be used in a 6502 computer?

Yes

> And if so, what is the upper limit (ie., max amount of memory)?
> Can I use a 1MB chip?
> Could I use one with more memory?

Any size is fine, but since the 6502 only has a 16 bit address bus you'll never be able to see more than 64k at a time - so a 1MB part would require paging or some such other scheme.

> Any info/help would be appreiciated.

All standard stuff - web searches and basic electronics books will cover these topics,
Sprow.

Could the 6502 be multiplexed? (or something LOL) Ie., can the 16 address pins have a circuit added to it to multiply the address pins that it can address by about ten-fold? Is this even possible or am I out of my head?
Thanks.
Lyos Norezel

If you can find an old pc mother board (don't know exactly which,
XT or around that time) some had a memory mapper, 74612
(I think it was), you might be able to salvage.

There's also a memory mapper for the Z80

It seems simple enough. Set it up so you can write to the inputs of some 74xx chip as a register, and have it's output control the higher address lines of the memory.

For every extra address line added, you double the memory available. This was done very often on NES game cartridges, using standard or custom parts.
http://nesdev.icequake.net/rom.txt

But the CPU can only access the 'page' that's currently switched in. That's easy to deal with, just keep the code/data that's used together in the same page.