Re: Using large DRAM modules inside the C64

From: Gábor Lénárt (
Date: 2005-10-11 15:46:43

On Tue, Oct 11, 2005 at 02:25:04PM +0200, Baltissen, GJPAA (Ruud) wrote:
> Hallo Gábor,
> > I've tried to use SRAM module, which is much easy, since you
> > haven't need refresh :)
> 1) The largest SRAM I know of is 512 KB. And for 16 MB you still need 32 of
> them....

Yes, I don't realize the question of memory size requirement in the original 
mail, sorry. I don't want to have 16M, I would be happy even with 0.5Mb ;-)

> 2) I have loads of DRAM modules laying around and only one 512 KB SRAM.

Sure, but don't forget the timing/refresh problems caused by the difference
between DRAMs in C64 and DRAMs on a DIMM module, sure I'm very far from
being a DRAM expert but I don't think so it can be easily soldered somehow
into the memory sockets of C64 ... The first idea on use of SRAMs has come
to mind when I weary of learning the usage of DRAM (ras/cas generating,
refreshing, etc) and the difference about "modern" and "old" DRAMs. Sure,
it's quite possible that I miss something and using DRAM is easier than
I inmagine.

( The target system was not C64 for this idea of mine first, but Enterprise-128
  where "system bus" is 22 bit wide (4Mbyte) thanks to the MMU functionality
  of Dave chip. So it's very easiy to solder a simple SRAM for this bus, and
  additional memory can be used even without modifying any ROM (OS of EP detects
  memory first by scanning the address space for writable areas at "boot").
  Since EP used refresh functionality of Z80, it was problematic to use the
  original refresh source with larger DRAMs, and the ability of store data
  even after power off seems to be a good candidate for using SRAM instead.
  Anyway I've not tried this on EP nor on C64 yet ... )

> I'll keep you informed about this one.

Thanks in advance!

- Gábor

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