Re: C128 Ram Banks 2 and 3

From: Marko Mäkelä (
Date: 2001-02-22 08:31:26

On Thu, 22 Feb 2001 wrote:

> I have a vague memory of the C128 being expandable to 256k and the internet
> documents for C128 memeory banking talk about there being RAM banks 2 and 3.
> How does one expand their C128 in this way?

The way I did it was that I piggy-backed another MMU on top of the
original one and added some glue logic that swapped some data pins on the
second MMU (I think D6 and D7) when the memory configuration registers
were addressed.  The RAM bank selection signals (those that are connected
to -CAS on the RAM chips) from the new MMU were wired to RAM banks 2 and 3.

The document and the schematic diagram is at
The expansion consists of two independent expansions: one that expands
each RAM bank from 64k to 256k, and another that doubles the amount of RAM
banks from 2 to 4.


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