RE: Using large DRAM modules inside the C64

From: Baltissen, GJPAA (Ruud) (
Date: 2005-10-13 08:45:57

Hallo Spiro,

> Does the VIC really generate some refresh cycles?

Yes, it does. The problem is that I don't have any simple means to see what
is a refresch cycle and what isn't. Bigger RAMs then the 4164 use 9 or more
addressbits. And all these bits must be covered for refresh (with the
exception of the 41256). If the VIC accesses the DRAM and it is NOT a
refresh, all these extra bits need to be zero. If it is a refresh, the
bitpattern towards the extra pins has to be activated and I need a mechanism
to detect a roll-over of the original 8 bits so I can increase this bit

Using CAS-before-RAS would simplify things but then I still need to know
what is a refresh cycle and what isn't. And then I still ain't sure if the
VIC generates enough refresh cycles to refresh the complete DRAM in time.

I myself have made up my mind and decided to use the original 64 KB of DRAM
plus external DRAM. And the first 64 KB of this external DRAM simply aren't
used at all in the first place. 

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