Re: 16 MB REU clone

From: Professor Dredd (
Date: 2001-08-21 12:16:24


Todd may have more detailed information but in a
nutshell ...
The RAMLink combines the REU with any SIMMs installed
to create one large virtual address space. A RAM disk
partition is automatically created equal to the size
of the REU. A second partition is automatically
created equal to the size of any installed SIMMs.

Because 24-bit addressing is used, the combined
address space cannot exceed 16 MBytes. If more than 16
MB total RAM is installed, the entire REU will
represent the first partition and SIMM RAM will
represent the second partition up to 16 MB.

Theoretically, if a 16 MB REU were installed then no
SIMM RAM would be recognized by the system. The entire
virtual address space would be taken up by the
capacity of the REU. That is, assuming the RAMLink is
capable of DETECTING an REU greater than 2 MB. It all
comes down to the code used in the RAMLink
initialization to detect the REU.

--- Marko_Mäkelä <> wrote:
> Todd,
> > Sounds very good. I do ask for one thing, if it's
> not too much trouble;
> > Create a dipswitch arrangement where the user can
> select from 1, 2, 4, 8 or
> > 16Mb out of the 16Mb cartridge 'REU'.
> Hmm, why would you need that?  The high-order bits
> of the REU bank
> selection register are normally unassigned, and the
> 2 MB REU hack is
> implemented in such a way that the added bank
> selection bits cannot be
> read by the processor.  All memory in the REU sits
> behind the controller,
> and it can only be accessed by telling the
> controller to copy data
> between the C64 and the expansion memory.
> On the other hand, I don't know how the CMD RAMLink
> works, since I have
> never seen the device or its schematic diagram.

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