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From: Richard Atkinson
Date: 1998-09-16
Subject: Re: 256K RAM expansions

> > I've been thinking about RAM expansions again, and I had an idea for the
> > simplest 256K expansion possible... (or is it?)
>
> Well, Pekka Pessi had that idea already in 1987. He uses a MC 6821 PIA
> for bank-switching, and you have four 16kB banks. His expansion is for
> the C64, but I adapted it for the C128. See
> http://www.funet.fi/pub/cbm/documents/projects/memory/256kB/ for the C64
> expansion documents, or my document page
> (http://www.hut.fi/Misc/cbm/docs/) for the HTML version.

Doesn't that expansion remap A14 and 15, so that any of the 16 16K blocks can be in any of the four banks? This expansion leaves them directly connected to the multiplexors, so that each 16K bank has 4 of its own 16K blocks to choose from, and they cannot be remapped onto other banks.

> > If my idea works, I will expand a plus/4 and a C64 to 256K and maybe
> > even a C128 to 512K.
>
> If you have a spare MMU, you can even expand the C128 to 1 megabyte. I've
> done that.

MMUs are not spare! If I had one, I'd rather keep it in case one in a machine died. Commodore chips do seem to be incredibly short-lived.

While we're on the subject of sourcing spare chips, does anyone know where to get 8501 processors? I have 3 broken 264 machines, and in all cases their processors have died. One also has a flaky TED chip, but this is more unusual.

Richard.