The 16MB C64
Date: 2004-06-15 08:42:45

Hi All,

Well, having finally proven out my DRAM refresh scheme for internally
mounted 1, 4 or 16MB SIMMs on the weekend, I'm very close to finalising the
hardware side of this project. A bit of a project overview is given below,
but the main question I have at the moment is where to map in the control
registers I need. A logical choice for me is in the VIC I/O space (because
the device will be a VIC socket plug in), new registers $D03E and $D03F. I'm
looking at these registers being Write-Only so I can save some decode logic.
The original Transactor design used the $01 port, but I need more bits than
are available and this location does have some compatibility issues (GEOS's
calculator is one such example).

The questions I have are:
1) Will the VIC definitely ignore these writes (I presume it will not
address wrap and write to some existing VIC register)
2) Will a SuperCPU be able to write to this location (I am guessing that it
just writes through to all registers which are not its own special CPLD). I
want this expansion available to those users too. I don't have a SuperCPU to
3) Is there any other expansion which might already use these two registers
(I think the C65 had some extra registers.... what about the C-1)

Any comments appreciated.
- Nick

Project Overview:
* 30pin SIMM based RAM expansion (1Mb, 4Mb, 16Mb)
* Hidden refresh scheme
* Common memory approach similar to C256 of Transactor design
* Single board plug-in replacement for VIC (original VIC gets PiggyBacked)
plus some jumper clips for extra address lines
* Control registers in VIC I/Ospace
* All logic integrated into a single CPLD (44pin)
* Internally addressible - available for VIC graphics and usable by external
processors also.

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